Part 7: For Curious Readers & Researchers

August 22, 2025

This section provides thorough documentation for the Dahlia Tubers Demystified series. Here, you'll find the scientific basis for every substantive claim, principle, and conclusion presented in Parts 1–6, and we include direct references to peer-reviewed research and authoritative texts. Our aim is to offer full transparency and encourage further exploration of dahlia physiology.

Due to the length of this article, readers may wish to use the Table of Contents (below) which provides convenient hyperlinks to the various sections that are included.

Recap: What the Series Covered Glossary Scientific Claims and Supporting Documentation From Part 1: What Makes a Tuber a Tuber? Claim 1.1: Dahlia tubers are storage organs that allow the plant to survive adverse conditions and regrow. Claim 1.2: Unlike true bulbs or corms, dahlia tubers are swollen adventitious roots, not modified stems. Claim 1.3: Tuber formation in dahlias specifically involves the reprogramming of certain adventitious roots under specific environmental and hormonal cues. Text block From Part 2: What Makes a Dahlia Root Become a Tuber? Claim 2.1: Tuber formation in dahlias is largely influenced by photoperiod (daylength), typically favored by shorter days. Claim 2.2: Cooler soil temperatures also contribute to robust tuber development. Claim 2.4: The critical window for tuber initiation typically occurs 4 to 8 weeks after planting, influenced by these environmental cues. Claim 2.5: Hormonal balance, particularly the interaction between gibberellins (GAs) and abscisic acid (ABA), is key to tuberization. High GAs inhibit, while ABA promotes. From Part 3: Why Some Dahlia Cuttings Don’t Make Tubers Claim 3.1: High light intensity, particularly long daylength, and warmth during propagation of cuttings can suppress tuber formation. Claim 3.2: Hormonal treatments, such as high levels of auxins used for rooting, can sometimes interfere with subsequent tuberization. Claim 3.3: The physiological age of the cutting material (juvenility) can also influence its capacity for tuber formation. Claim 3.4: Practices like taking cuttings too late in the season, when mother plants are already signaling tuberization, can improve tuber yield from cuttings. From Part 4: Disrupted Tuber Formation: What’s Really Going On? Claim 4.1: Commercial growth regulators (CGRs) are used to manipulate plant architecture (e.g., height, branching) and flowering time for market purposes, which can have downstream effects on tuber formation. Claim 4.2: Specific CGRs like Ethephon, Daminozide (Alar), SADH, and Maleic Hydrazide (MH) impact plant growth by altering hormonal balances, potentially affecting resource allocation for tuber development. Claim 4.3: Dahlias purchased as potted plants from garden centers may have been treated with CGRs, which can alter their initial growth habit and potentially delay or reduce tuberization compared to tubers grown for propagation. From Part 5: Are Tuber Traits Genetic? Claim 5.1: Tuber formation in dahlias is a polygenic trait, meaning it is influenced by multiple interacting genes rather than a single gene. Claim 5.2: Different dahlia cultivars exhibit varying tendencies for tuber size, shape, eye formation, and storability, even under ideal conditions, due to genetic differences. Claim 5.3: Breeders can select for tuber-forming traits through seedling selection over generations. From Part 6: The Science of Better Tuber Harvests Claim 6.1: Cool, moist soil and shortening daylength are key triggers for robust tuber formation. Claim 6.2: Excess artificial light or high nitrogen fertilizer early on can delay or suppress tuber formation. Claim 6.3: Integrated nutrient management, combining inorganic fertilizers with organic manures and bio-inoculants, significantly improves plant growth and tuber yield in dahlias. Claim 6.4: Phosphorus is fundamental for root development and energy transfer, foundational for tuber formation, while Potassium is vital for carbohydrate transport and storage, directly impacting tuber bulking. Claim 6.5: Allowing plants to grow for a week or two after blooming slows, as long as frost hasn't killed foliage, can promote continued tuber swelling and eye formation. Online Resources Full Bibliography AI Collaboration Transparency

Recap: What the Series Covered

Before diving into the sources, here’s a brief overview of the key topics explored throughout this series:

What Makes a Tuber a Tuber: We began by breaking down the biological difference between ordinary roots and those capable of swelling into tubers. Dahlia tubers aren’t formed at random. They emerge when specific adventitious roots are reprogrammed under just the right environmental and hormonal cues.

Environmental Timing: We explored the critical 4 to 8 week window when tubers begin to form. Soil temperature, daylength, and moisture all play essential roles. Gardeners who time planting right can influence whether a dahlia builds strong, storable tubers or roots that are weak and stringy.

Suppression, Breeder Tools, and Hormonal Interference: We looked at how the formation of tubers by dahlias can be suppressed, sometimes intentionally, sometimes by accident, through light exposure, hormones, temperature, and other propagation techniques. While useful in labs and commercial propagation, these tools carry risks when growers use them outside controlled environments.

Genetic Influence and Cultivar Behavior: Not all dahlias are created equal. We examined how genetics influence tuber shape, eye formation, and storability, and why some dahlias consistently produce strong results while others struggle, even under ideal conditions.

Controversies, Growth Regulators, and the Unknown: We explored the gray areas of dahlia tuber manipulation: the use of chemical growth regulators in commercial production, unexplained failures in tuber formation, and the frustration growers feel when healthy dahlias still don’t produce viable tubers.

The Science of Better Tuber Harvests: We explored practical advice to help you apply what you’ve learned, including insights into nutrient management and how environmental factors can be optimized for larger, healthier clumps.

Glossary

This glossary provides definitions for key terms and concepts used throughout the Dahlia Tubers Demystified series. It is designed to clarify specialized vocabulary and enhance your understanding of dahlia tuber biology and cultivation.

Abscisic acid (ABA) — A plant hormone that promotes tuber formation and maturation. Higher levels of ABA are often associated with better tuber development in dahlias.

Adventitious roots — Roots that arise from non-root tissue (such as stems or leaf nodes) rather than from the primary root system. In dahlias, only some adventitious roots have the potential to form tubers.

Auxins — Growth hormones involved in root development, cell elongation, and other processes. While not directly responsible for tuber formation, auxins interact with other hormones like gibberellins.

Blind tubers — Tubers that form but lack a visible "eye" (growth point), rendering them unable to sprout new plants for the next season. Their formation is not a failure of tuber development itself, but a lack of a viable growth bud.

Commercial Growth Regulators (CGRs) — Synthetic chemical compounds applied in commercial plant production to manipulate plant growth, height, branching, or flowering time. While useful for retail aesthetics, they can sometimes have unintended effects on tuber formation in dahlias.

Crown — The thickened base of a dahlia stem where the tubers attach and from which new sprouts (eyes) emerge for the next growing season. It is a critical part for overwintering and successful regrowth.

Feeder roots — Thin, fibrous roots that absorb water and nutrients but do not swell into tubers. Some dahlia plants produce mostly feeder roots with little or no tuber formation.

Gibberellins (GA) — Plant hormones that promote vegetative growth, such as stem elongation. High levels of GA can inhibit or delay tuber formation in dahlias.

Hormone balance — The interaction of different plant hormones that regulate growth, development, and the formation of tubers. A shift from gibberellin dominance to abscisic acid dominance is often required for tubers to form.

Integrated Nutrient Management (INM) — A holistic approach to plant nutrition that combines various methods, including inorganic fertilizers, organic amendments (like manure or compost), and beneficial bio-inoculants (microbes), to optimize nutrient availability and plant health.

Mycorrhizae — A symbiotic relationship between fungi and plant roots, where both organisms benefit. The fungi extend the plant's root system, enhancing nutrient and water uptake, while the plant provides the fungi with sugars and other carbohydrates.

Node — A point on the stem where leaves, branches, or buds form. In dahlias, tuber eyes often develop near nodes at the crown.

NPK — An acronym representing the three primary macronutrients essential for plant growth: Nitrogen (N), Phosphorus (P), and Potassium (K). The ratio of these nutrients significantly influences dahlia growth, flowering, and tuber development.

Photoperiod — The duration of light and dark periods within a 24-hour cycle. Photoperiod is a critical environmental cue that influences various plant processes, including tuber formation in dahlias.

Polygenic trait — A characteristic influenced by multiple interacting genes, rather than a single gene. Tuber formation is considered a polygenic trait in dahlias.

Seedling selection — A breeding method where new dahlia plants grown from seed are evaluated for desirable traits—both above and below ground—before being kept for future propagation.

Short-day plants — Plants that initiate flowering or tuberization when the period of daylight is shorter than a critical length. Dahlias are considered short-day plants in terms of their tuber formation, responding to the shortening days of late summer and early fall.

Storage organ — An underground plant structure (like a tuber, bulb, or rhizome) that stores nutrients and energy. In dahlias, tubers serve as storage organs for overwintering and regrowth.

Tuber / Tuberization — A tuber is a swollen underground storage organ formed from certain roots. Tuberization is the biological process by which adventitious roots transform into tubers.

Tuber eye — The bud on a dahlia tuber from which new growth emerges. Viable eyes are essential for successful propagation.

A large dahlia tuber clump showing stems and roots

Scientific Claims and Supporting Documentation

This section presents the direct scientific evidence supporting every substantive claim and conclusion in Dahlia Tubers Demystified (Parts 1–6). Each numbered claim from the series is listed here, along with direct links to the relevant peer-reviewed research articles and authoritative texts.

Use this section to explore the scientific foundations behind the discussions.

Most sources were reviewed in full. Where only the abstract was available, the citation is marked with “Abstract only accessed.” Full hyperlinks are provided for all sources. When an article is behind a paywall, it is noted as “Academic Paywall” for readers who may have institutional access.

From Part 1: What Makes a Tuber a Tuber?

Claim 1.1: Dahlia tubers are storage organs that allow the plant to survive adverse conditions and regrow.

Ciobanu, I., Cantor, M., Stefan, R., Buta, E., Magyari, K., & Baia, M. (2016). The influence of storage conditions on the biochemical composition and morphology of dahlia tubers . Notulae Botanicae Horti Agrobotanici Cluj-Napoca, 44(2), 459-465.

The article states that "While Dahlias thrive in frost-free climates, their tuberous roots can endure dormancy periods, allowing cultivation in temperate climates via the lifting and storing of the tubers during winter". It also notes that "carbohydrates stored in the tuberous roots (particularly inulin in the case of Dahlia) ensures the perennial trait of the plant and has direct influence on early growth in the new season". This directly supports the tubers' role as storage organs for survival and regrowth.

Moldovan, I., Cotoz, A. P., Rózsa, S., Magyari, K., Lehel, L., Baia, M., & Cantor, M. (2024). The Influence of Technological Factors on the Structure and Chemical Composition of Tuberous Dahlia Roots Determined Using Vibrational Spectroscopy . Plants, 13(14), 1955.

The introduction states that "While Dahlias thrive in frost-free climates, their tuberous roots can endure dormancy periods, allowing cultivation in temperate climates via the lifting and storing of the tubers during winter". This directly implies their role as storage organs for survival and regrowth across seasons.

Aoba, T., Watanabe, S., & Saito, C. (1960). Studies on tuberous root formation in dahlia. I Periods of tuberous root formation in dahlia . Journal of the Japanese Society for Horticultural Science, 29(3), 247-252. (Author’s note: Written in Japanese. English translation provided by Gemini AI and verified by ChatGPT 4o.)

The summary states that "the adventitious roots developed in the tuberous roots". The study investigates the "process of tuberous root formation" which by definition implies the development of storage organs for the plant's life cycle.

TUCHIYA, S. (1993). Studies on the Production of Tuberous Roots in Dahlia . Special bulletin of Ishikawa Agricultural College, 18, 70-73.

The summary and various sections discuss "tuberous roots" as means of survival and "seed tuberous roots" for subsequent growth, implying their storage function for survival and regrowth.

Menzel, C. M. (1985). The control of storage organ formation in potato and other species: a review. Part 2 .

The review broadly discusses storage organ formation across various species (including dahlia mentioned in Table 4 and 5), focusing on their development as energy reserves for survival and regrowth. The abstract states the review is on "the control of storage organ formation".

Claim 1.2: Unlike true bulbs or corms, dahlia tubers are swollen adventitious roots, not modified stems.

Aoba, T., Watanabe, S., & Soma, K. (1961). Studies on the formation of tuberous root in dahlia. II Anatomical observation of primary root and tuberous root . Journal of the Japanese Society for Horticultural Science, 30(1), 82-88. (Author’s note: Written in Japanese. English translation provided by Gemini AI and verified by ChatGPT 4o.)

The article states its purpose is to show that "tuberous roots are enlarged adventitious roots" and that "primary root... is not the enlarged part of a root". It details the anatomical structure of adventitious roots developing into tuberous roots, confirming they are derived from roots and not other stem structures.

The article consistently refers to the storage structures as "tuberous roots" and states that "The adventitious root and tuberous root have similar anatomical structure, and they are distinguished from the normal fibrous roots". It clarifies that what are "called tuberous roots are enlarged adventitious roots".

Menzel, C. M. (1985). The control of storage organ formation in potato and other species: a review. Part 2.

This review differentiates various storage organs, implicitly supporting the classification of dahlia tubers as modified roots. While it doesn't explicitly compare dahlias to bulbs/corms as modified stems, it discusses "tuberization" of roots in many species.

The article consistently refers to the plant structures as "tuberous roots", and describes their internal "structure of the primary root" including cortex and parenchyma layers, which is consistent with root morphology.

TUCHIYA, S. (1993). Studies on the Production of Tuberous Roots in Dahlia . Special bulletin of Ishikawa Agricultural College, 18, 70-73.

While the article doesn't explicitly compare to bulbs/corms, it consistently refers to them as "tuberous roots" and describes their formation and development from the root system.

Zimmerman, P. W., & Hitchcock, A. E. (1929). Root formation and flowering of dahlia cuttings when subjected to different day lengths . Botanical Gazette, 87(1), 1-13.

The article consistently refers to the storage organs formed in response to short days as "storage roots". It also details how various parts of the stem (basal ends, lowest buds) and even leaf petioles can become "storage organs", suggesting a broader origin for storage tissue in dahlias beyond typical fibrous roots.

Claim 1.3: Tuber formation in dahlias specifically involves the reprogramming of certain adventitious roots under specific environmental and hormonal cues.

The article explains that the thickening of adventitious roots occurs through "cell division... and by the elongation of these cells, then adventitious roots develop into the tuberous roots". It describes the formation of a cambium ring and secondary xylem formation as key anatomical processes in this development.

Biran, I., Leshem, B., Gur, I., & Halevy, A. H. (1974). Further studies on the relationship between growth regulators and tuberization of dahlias . Physiologia Plantarum, 31(1), 23-28. Abstract only accessed. Academic Paywall.

The abstract describes "tuberization" as being "caused by inter-fascicular cambial activity producing parenchyma cells inward". It also notes that "Short-day conditions which promote tuberization, increased the endogenous level of ABA-like inhibitors in intact plants", directly linking environmental cues (short-days) and a hormonal response (ABA increase) to the anatomical process of tuber formation.

Halevy, A. H., & Biran, I. (1974, April). Hormonal regulation of tuberization in Dahlia . In II International Symposium on Flower Bulbs 47 (pp. 319-330). Abstract only accessed. Academic Paywall.

The abstract states that "Short day conditions which promote tuberization increased the endogenous level of ABA. Evolution of endogenous ethylene reached a peak... one week before the onset of tuberization". This links environmental cues (short day) and hormonal changes (ABA and ethylene peaks) directly to the initiation of tuberization.

Biran, I., Gur, I., & Halevy, A. (1972). The relationship between exogenous growth inhibitors and endogenous levels of ethylene, and tuberization of dahlias . Physiologia Plantarum, 27(2), 226-230. Abstract only accessed. Academic Paywall.

The abstract discusses that "Evolution of endogenous ethylene reached a peak... after the start of short-day treatments... The peak in ethylene evolution occurred one week before the onset of tuberization". This indicates that environmental cues (short-days) trigger a hormonal response (ethylene peak) that precedes and is associated with the onset of tuberization.

Brøndum, J. J., & Heins, R. D. (1993). Modeling temperature and photoperiod effects on growth and development of dahlia . JOURNAL-AMERICAN SOCIETY FOR HORTICULTURAL SCIENCE, 118, 36-36.

The article's introduction notes that "SD [short day]... promot[es] tuberous root formation". The "Results" section, under "Tuberous root weight", explicitly states: "Temperature and photoperiod affected tuberous root formation". This demonstrates that environmental factors (temperature and photoperiod) are cues influencing tuber formation.

Legnani, G., & Miller, W. B. (2001). Using photoperiod to manipulate flowering and tuberous root formation in seed Dahlias . Greenh. Prod. New, 11(13), 36-40.

The article states in its introduction that "Tuberous root development and flower induction of Dahlia are controlled by photoperiod". It also describes "Adventitious tuberous roots originated from the swollen base of the stems independent of fibrous roots". This indicates a specific process and origin influenced by an environmental cue (photoperiod).

TUCHIYA, S. (1993). Studies on the Production of Tuberous Roots in Dahlia . Special bulletin of Ishikawa Agricultural College, 18, 70-73.

The study investigates "influences of time of planting and harvesting, daylength and nutrients on the formation of tuberous roots", and describes how roots thicken to become storage organs, implying a transformation.

From Part 2: What Makes a Dahlia Root Become a Tuber?

Claim 2.1: Tuber formation in dahlias is largely influenced by photoperiod (daylength), typically favored by shorter days.

Brøndum, J. J., & Heins, R. D. (1993). Modeling temperature and photoperiod effects on growth and development of dahlia . JOURNAL-AMERICAN SOCIETY FOR HORTICULTURAL SCIENCE, 118, 36-36.

The study's results on tuberous root weight indicate that tuberous roots formed on plants in 10 and 12-hour photoperiod treatments at 15 and 20C, while only small tuberous roots formed or none at all when the photoperiod was 14 hours or longer, showing that longer photoperiods suppress tuber formation. The "Discussion" section further confirms that "Low temperature and SD promoted tuberous root formation", directly indicating that shorter photoperiods favor increased tuberous root weight.

Zimmerman, P. W., & Hitchcock, A. E. (1929). Root formation and flowering of dahlia cuttings when subjected to different day lengths . Botanical Gazette, 87(1), 1-13.

The entire study investigates this relationship, explicitly concluding that "Length of day determines the type of root system formed by cuttings for 6 varieties of dahlia, heavy root storage being correlated with a short day, and a fibrous root system being correlated with a long day".

Legnani, G., & Miller, W. B. (2000). Night Interruption Lighting Is Beneficial in the Production of Plugs of Dahlia Sunny Rose' . HortScience, 35(7), 1244-1246.

The study states that "Tuberous root development... are controlled by photoperiod". It also explicitly finds that "SD [short day] increased tuberous root development at the expense of shoot growth" and that "Tuberous root dry weight was 2.4-fold as great in SD than in LD plugs".

Konishi, K., & Inaba, K. (1964). Studies on flowering control of dahlia. I. On optimum day-length . Journal of the Japanese Society for Horticultural Science, 33(2), 171-180. (Author’s note: Written in Japanese. English translation provided by Gemini AI and verified by ChatGPT 4o.)

The "Summary" notes in its findings that "short day treatment (8-hour photoperiod for 20 or 40 days) reduced the number of roots and increased the diameters of roots". This directly supports that shorter daylengths favor the thickening of roots into tubers (increased diameter).

TUCHIYA, S. (1993). Studies on the Production of Tuberous Roots in Dahlia . Special bulletin of Ishikawa Agricultural College, 18, 70-73.

Chapter 3 is titled "Influence of Daylength on the Formation and Thickening of Tuberous Roots" , and states that "short-day condition[s] stimulated tuberous root formation" and led to heavier, more uniform roots. It also mentions the need for a period under long-day conditions followed by short-day for heavy tuber production.

Legnani, G., & Miller, W. B. (2001). Using photoperiod to manipulate flowering and tuberous root formation in seed Dahlias . Greenh. Prod. New, 11(13), 36-40.

The introduction states that "Tuberous root development and flower induction of Dahlia are controlled by photoperiod". The results show "SD increased tuberous root development at the expense of shoot growth" and that "SD plugs had developed large, rounded, tuberous roots while LD plugs had produced slender, elongated structures".

Experiment 3, titled "Influence of photoperiod on the growth of roots in dahlia seedlings", found that "The short day treatment (8-hour photoperiod for 20 or 40 days) reduced the number of roots and increased the diameters of roots". This directly links short days to increased tuberous root thickening (diameter).

Menzel, C. M. (1985). The control of storage organ formation in potato and other species: a review. Part 2.

The review broadly states under "7 Conclusions" that "In most species and cultivars so far examined, short photoperiods... promote storage-organ formation and reduce shoot growth, while long photoperiods... restrict storage-organ formation and promote shoot growth". Dahlia variabilis is listed in Table 4 as a species where storage-organ formation is reduced or delayed by gibberellins (which are influenced by photoperiod).

Halevy, A. H., & Biran, I. (1974, April). Hormonal regulation of tuberization in Dahlia . In II International Symposium on Flower Bulbs 47 (pp. 319-330). Abstract only accessed. Academic Paywall.

The abstract directly states "Short day conditions which promote tuberization", indicating the strong influence of shorter daylengths on tuber formation.

The abstract states that "Short-day conditions which promote tuberization, increased the endogenous level of ABA-like inhibitors in intact plants", directly indicating that short-day conditions favor tuberization.

The abstract states that the "effect [of various growth inhibitors] was smaller, however, than the effect short days have on tuberization", directly indicating that short days have a strong promoting effect on dahlia tuberization.

Ivanova, V., & Zaprjanova, N. (2020). Study on phenological behaviours of Dahlia variabilis Hort. in overwintering of tuberous roots in the soil .

The article states that "In most studies, light is the main factor influencing its development and especially on flowering". While this specific study focuses on overwintering rather than directly manipulating daylength for tuber formation, its acknowledgment of light as a main factor in dahlia development aligns with the general influence of photoperiod.

Claim 2.2: Cooler soil temperatures also contribute to robust tuber development.

Brøndum, J. J., & Heins, R. D. (1993). Modeling temperature and photoperiod effects on growth and development of dahlia . JOURNAL-AMERICAN SOCIETY FOR HORTICULTURAL SCIENCE, 118, 36-36.

The study's results indicate that tuberous roots formed on plants in photoperiod treatments at 15 and 20C, whereas no tuberous roots formed at 25 and 30C regardless of photoperiod. The "Discussion" section explicitly states that "Low temperature and SD promoted tuberous root formation" and specifically notes that "15C promotes tuberous root formation".

Menzel, C. M. (1985). The control of storage organ formation in potato and other species: a review. Part 2.

The "7 Conclusions" section states that "low temperatures... promote storage-organ formation and reduce shoot growth, while... high temperatures... restrict storage-organ formation". The review discusses how high temperatures increase gibberellin levels, which inhibit tuberization.

Schneck, K. K., Boyer, C. R., & Miller, C. T. (2021). Supraoptimal Root-zone Temperatures Affect Dahlia Growth and Development . HortTechnology, 31(6), 667-678.

The article extensively studies the negative effects of supraoptimal (hot) root-zone temperatures (RZTs) on dahlias, leading to root decline. While it doesn't directly state "cooler temperatures contribute to robust tuber development," the inverse is strongly implied by its findings that higher temperatures cause decreased root quality and overall plant height. The study's control group was at ≈22°C (optimal range).

Fernandes, M. E. S., Tomiozzo, R., Freitas, C. P. D. O. D., Roso, T. P., Sousa, M. H. L. D., Uhlmann, L. O., ... & Streck, N. A. (2023). Damage and lethal temperature due to heat stress in field grown dahlia . Ornamental Horticulture, 29(2), 216-223.

While the study primarily focuses on photoperiod and defoliation, the general observation that tuberous root thickening was "especially after October" (when temperatures naturally cool in many growing regions) provides indirect support for cooler temperatures contributing to development.

Claim 2.3: Soil moisture and drainage are critical; waterlogging can inhibit tuber formation by reducing oxygen to the roots.

Jędrzejuk, A., Bator, M., Werno, A., Karkoszka, L., Kuźma, N., Zaraś, E., & Budzynski, R. (2022). Development of an algorithm to indicate the right moment of plant watering using the analysis of plant biomasses based on Dahlia× hybrida . Sustainability, 14(9), 5165.

The study focuses on optimizing water use efficiency and preventing overwatering. It states that "The proper irrigation scheduling, that is, just before the plant loses turgor... makes it possible to save ca. 30% of irrigation water, in comparison to standard watering". This implies that excessive watering (which can lead to waterlogged conditions) is a problem to be avoided, aligning with the idea that proper moisture management is critical for plant health, including root health.

Ali, E. O. H. (2004). Pathological studies on dahlia tuber rots (Doctoral dissertation, Department of Agricultural Botany, Faculty of Agriculture at Moshtohor, Zagazig University).

The thesis focuses on fungal and bacterial diseases affecting dahlias, including "rotted dahlia tubers" and their destruction. It details the identification of various pathogens (e.g., Sclerotium rolfsii, Fusarium solani, Erwinia carotovora) that attack dahlia tubers. The occurrence of such rots in tubers, often exacerbated by waterlogged or poorly drained conditions, directly highlights a significant factor that can "disrupt tuberization" by destroying the tubers, thereby implicitly supporting that proper drainage is critical.

Joe Gardener Podcast episode 283-A Soil Chemistry Primer: How Protons and Electrons Influence Soil Moisture and Fertility is a conversation with retired horticulture professor Debbie Flower, who holds a bachelor’s in plant science from Rutgers University in New Jersey and a master’s in urban horticulture from UC Davis in California.

Describing waterlogged soil, Flower says “Not only is the water around the outside of the particles, it’s filling the spaces between the particles. There is no room for oxygen, and roots have to have oxygen.” If the roots go too long without oxygen, which means they can’t perform respiration, the plant will experience root rot.

Claim 2.4: The critical window for tuber initiation typically occurs 4 to 8 weeks after planting, influenced by these environmental cues.

TUCHIYA, S. (1993). Studies on the Production of Tuberous Roots in Dahlia . Special bulletin of Ishikawa Agricultural College, 18, 70-73.

The article states "Seventy percent of the tuberous roots formed during [the] growing period [had] appeared by midd-July, within 2.5 months after planting". It also notes that "the number of roots appearing by midd-July is important for obtaining useful tuberous roots as seeds", which is approximately 2.5 months (10-11 weeks) after a common spring planting, indicating a critical early period.

Kumar, M., Thakur, P., Kashyap, B., Kumar, P., Sharma, A., Bhardwaj, R., ... & Shah, A. H. (2024). Effect of Different Planting Dates on Tuber Production in Dahlia (Dahlia variabilis L.) in Low Hill Conditions of Himachal Pradesh, India . Plant Cell Biotechnology and Molecular Biology, 25(7-8), 71-78.

The study investigates the "Effect of different planting dates on tuber production" and found that "The planting date of October 15th was identified as highly suitable for optimal tuber production across all parameters". This demonstrates that the timing of planting, influenced by environmental cues, is a critical factor for tuber formation.

Menzel, C. M. (1985). The control of storage organ formation in potato and other species: a review. Part 2.

The review extensively discusses the role of environmental factors (photoperiod, temperature, nitrogen) in "tuber initiation" and "storage-organ formation" across various species, emphasizing that these cues trigger the process.

ędrzejuk, A., Bator, M., Werno, A., Karkoszka, L., Kuźma, N., Zaraś, E., & Budzynski, R. (2022). Development of an algorithm to indicate the right moment of plant watering using the analysis of plant biomasses based on Dahlia× hybrida . Sustainability, 14(9), 5165.

Ali, E. O. H. (2004). Pathological studies on dahlia tuber rots (Doctoral dissertation, Department of Agricultural Botany, Faculty of Agriculture at Moshtohor, Zagazig University).

Claim 2.5: Hormonal balance, particularly the interaction between gibberellins (GAs) and abscisic acid (ABA), is key to tuberization. High GAs inhibit, while ABA promotes.

Elsadek, A. (2018). Improvement yield and quality of dahlia flowers by exogenous application of gibberellic acid and salicylic acid under sandy soil conditions . Journal of Plant Production, 9(3), 289-297.

The study directly investigates the effect of Gibberellic Acid (GA3) and Salicylic Acid (SA) , which are plant hormones. Its findings show that treatments with GA3 (e.g., 200 ppm) significantly increased tuber length, number of tubers per plant, and tuber fresh/dry weight. SA treatments also enhanced tuber formation. This demonstrates that these hormones (GA, SA) directly influence tuberization and contribute to the overall hormonal balance affecting this process.

Menzel, C. M. (1985). The control of storage organ formation in potato and other species: a review. Part 2.

The review dedicates sections to "Gibberellins" and "Abscissic acid" and their roles in tuberization. It explicitly states, "The results of most of the investigations reported are consistent with the hypothesis that gibberellins are synthesized in the non-induced plant and inhibit tuber formation directly at the stolon tip". Conversely, it notes, "Exogenous ABA promoted tuberization when applied to non-induced tissues". It concludes that "low gibberellin and high cytokinin and/or high inhibitor levels" are associated with tuber conversion.

The abstract directly states that "Abscisic acid (ABA)... promoted the growth of tuberous roots" and "GA treatment inhibited the growth of tubers and roots". It further suggests that "GA and ABA directly control tuberization" and that "ABA levels which increased under short-day conditions seem to produce a sink in the roots. GA probably inhibits tuberization by interfering with the trans-location of photosynthates to the root area". This strongly supports the antagonistic roles of ABA (promoting) and GA (inhibiting) in tuberization.

Halevy, A. H., & Biran, I. (1974, April). Hormonal regulation of tuberization in Dahlia . In II International Symposium on Flower Bulbs 47 (pp. 319-330). Abstract only accessed. Academic Paywall.

The abstract explicitly states that "ABA enhanced tuberization and GA inhibited it both in whole plants and in budless cuttings". It further suggests that "GA and ABA directly control tuberization by determining the site of the sink for assimilates".

The abstract explicitly states that "Treatments with abscisic acid (ABA)... promoted the tuberization" and, in contrast, "gibberellic acid (GA) treatments inhibited tuberization". This directly supports the roles of ABA as a promoter and GA as an inhibitor of tuberization.

Menzel, C. M. (1985). The control of storage organ formation in potato and other species: a review. Part 1. Abstract only accessed. Academic Paywall.

The abstract indicates that "storage-organ formation is controlled directly by a hormonal stimulus" and that "in most cases it appears that storage-organ formation is associated with low gibberellin and high cytokinin and/or high inhibitor levels".

TUCHIYA, S. (1993). Studies on the Production of Tuberous Roots in Dahlia . Special bulletin of Ishikawa Agricultural College, 18, 70-73.

While not explicitly naming GAs or ABA, Chapter 5 discusses "6-benzylaminopurine sprays during the vigorous growing period... increased the number of buds at the base of [the] stem. This resulted in increasing useful tuberous roots...". This points to the influence of specific hormonal substances on tuber development.

Suma, B. (1993). Effect of growth retardants on growth, flowering, vase-life and tuber formation of dahlia (Dahlia variabilis Desf.) propagated through cuttings (Doctoral dissertation, Kerala Agricultural University).

The "Results and Discussion" section for plant height mentions that the reduction in height by CCC and Alar "may be attributed to inhibition of cell elongation and reduction in gibberellin synthesis, which are well-documented effects of CCC and Alar". This directly discusses the impact of growth retardants on gibberellin, a key hormone, affecting plant growth.

Mills-Ibibofori, T., Dunn, B. L., Maness, N., & Payton, M. (2019). Effect of LED lighting and gibberellic acid supplementation on potted ornamentals . Horticulturae, 5(3), 51.

The study directly investigates the effect of gibberellic acid (GA3) on dahlia. Its findings demonstrate that GA3 treatments significantly increased plant height (e.g., dahlia height increased from 17.5 cm to 30.2 cm with 150 mg L-1 GA3 under LED flowering lamps), and influenced flower number. This supports that GA (a key hormone) impacts overall plant growth and flowering in dahlias, which relates to the broader concept of hormonal balance influencing plant development.

Pal, S. L. (2019). Role of plant growth regulators in floriculture: An overview . J. Pharmacogn. Phytochem, 8, 789-796.

As an overview on Plant Growth Regulators, the article discusses the major classes of plant hormones, including Gibberellins (GAs) and Abscisic acid (ABA) . It states that "Gibberellins promotes stem elongation, flowering and fruit development" and "Abscisic acid (ABA) is a plant growth inhibitor which induces dormancy". This review broadly supports the roles of GAs as growth promoters and ABA as a dormancy-inducing inhibitor, contributing to the understanding of hormonal balance.

Kumar, T., Rinu, R. S., & Praddyum, S. T. A comprehensive review of Plant Growth Regulators (PGRs) and their impact on flowering and ornamental crops with insights into effective application methods.

As a comprehensive review of PGRs, the article discusses the major classes of plant hormones, including Auxins, Gibberellins (GAs), Cytokinins, Abscisic Acid (ABA), and Ethylene . It details their physiological mechanisms, stating that Gibberellins promote stem elongation, while Abscisic Acid is a "plant growth inhibitor which induces dormancy". This provides general support for the roles of GAs as growth promoters and ABA as a dormancy-inducing inhibitor, contributing to the understanding of hormonal balance.

From Part 3: Why Some Dahlia Cuttings Don’t Make Tubers

Claim 3.1: High light intensity, particularly long daylength, and warmth during propagation of cuttings can suppress tuber formation.

Brøndum, J. J., & Heins, R. D. (1993). Modeling temperature and photoperiod effects on growth and development of dahlia . JOURNAL-AMERICAN SOCIETY FOR HORTICULTURAL SCIENCE, 118, 36-36.

The study's results on tuberous root weight indicate that while tuberous roots formed in 10 and 12-hour photoperiod treatments at 15 and 20C, only small tuberous roots formed or none at all when the photoperiod was 14 hours or longer, showing that longer photoperiods suppress tuber formation. The "Discussion" section emphasizes that "Photoperiods <12 h promote tuberous root formation and inhibit vegetative and reproductive shoot growth", implying the inverse for longer days. It also found that temperatures of "25C or higher reduce or prevent flowering entirely", and that "No tuberous roots were formed, regardless of photoperiod, at 25 and 30C", directly connecting warmth with the suppression of tuber formation.

Legnani, G., & Miller, W. B. (2000). Night Interruption Lighting Is Beneficial in the Production of Plugs of Dahlia Sunny Rose' . HortScience, 35(7), 1244-1246.

The article investigates using "night interruption lighting" to create long-day (LD) conditions for dahlia plug production. It explicitly concludes that "Night interruption lighting during dahlia plug production can... inhibit tuberous root growth" and that under LD, there was "reduced growth of tuberous roots". The results show "No tuberous root formation was evident at week 2" in both LD and SD, but by week 4 and 6, SD plugs had greater tuberous root dry weight, whereas LD plugs had less, supporting that long days suppress tuber formation.

Zimmerman, P. W., & Hitchcock, A. E. (1929). Root formation and flowering of dahlia cuttings when subjected to different day lengths . Botanical Gazette, 87(1), 1-13.

The study found that plants given "extra light" produced "normal fibrous roots only" and "did not form storage organs". It states that "extra light most completely eliminated formation of storage roots" , and "Cuttings grown earlier in the season, when the days were longer, had no such tendency toward developing storage organs. Normal fibrous roots were the rule".

The "Summary" states that "The growth of shoot was inhibited under the day-length shorter than 12 hours, while it was enhanced under that longer than 13 hours". This confirms that longer daylengths promote vegetative shoot growth, implying a diversion of energy away from tuber formation, consistent with suppression.

Legnani, G., & Miller, W. B. (2001). Using photoperiod to manipulate flowering and tuberous root formation in seed Dahlias . Greenh. Prod. New, 11(13), 36-40.

The article discusses "night interruption lighting" being used "to inhibit tuberous root formation" in plug production, which creates long-day (LD) conditions. It states that under LD, "reduced growth of tuberous roots" was observed.

Read, P. E., Dunham, C. W., & Fieldhouse, D. J. (1972). Increasing Tuberous Root Production in Dahlia pinnata Cav. with SADH and Chlormequat1 . HortScience, 7(1), 62-63.

The article states that "Similar treatments under long-day conditions caused formation of tuberous roots where untreated cuttings produced only fibrous roots". This indicates that under long-day conditions, untreated dahlias primarily form fibrous roots, implying suppression of tuber formation, and the treatments overcame this suppression.

The abstract states that treatments with abscisic acid (ABA), SADH, or ethephon "promoted the tuberization of dahlia plants in long-days". This implies that long-day conditions themselves are normally suppressive to tuberization in dahlias, and these substances overcame that suppression.

The abstract notes that "Abscisic acid (ABA) and gibberellin (GA) treatments, applied to budless leaf cuttings of Dahlia under long day conditions, did not increase the total weight of the cuttings but did affect the region where photosynthates accumulate". This implies that long-day conditions are generally not conducive to tuberization, and substances like ABA and GA affect how resources are handled under these suppressive conditions.

Claim 3.2: Hormonal treatments, such as high levels of auxins used for rooting, can sometimes interfere with subsequent tuberization.

Sao, B., & Verma, L. S. (2021). Effect of rooting hormones in propagation of dahlia (Dahlia variabilis L.) through stem cutting . Journal of Pharmacognosy and Phytochemistry, 10(2), 887-891.

The study investigates the impact of auxins (IBA and NAA) on dahlia cuttings. While it focuses on promoting rooting, it demonstrates that exogenous auxin application "enhances the rooting efficiency and quality of stem cuttings". This directly illustrates the effect of hormonal treatments (auxins) on root development, which is a physiological process that can influence subsequent tuberization (though this article does not directly study tuberization impacts).

Singh, S., Singh, I., Miller, C. T., Dhatt, K. K., & Dubey, R. K. (2023). Increasing basal dose of indole-3-butyric acid improve rooting and growth of different cutting types in Dahlia . Rhizosphere, 27, 100729. Abstract only accessed. Academic Paywall.

The abstract directly investigates the "influence of IBA [indole-3-butyric acid, an auxin] on the rooting and growth characteristics of Dahlia cuttings". It states that "Exogenously applied IBA (1500 mg L−1) for 5 s influenced the rooting characteristics with considerably earlier (17.5 days) root initiation with more number (6.7) and longer length (11.5 cm) of roots". This explicitly supports that hormonal treatments (auxins) directly impact root development.

Menzel, C. M. (1985). The control of storage organ formation in potato and other species: a review. Part 2.

The review extensively details the effects of SADH (N-dimethylaminosuccinamic acid) and CCC (chlormequat) on various species (including dahlia), stating they "inhibit endogenous gibberellin synthesis and reduce gibberellin levels". It also discusses the mixed effects of ethylene (via CEPA) on tuberization and its influence on hormonal balance (e.g., C2H4 inhibiting root development which is a site of GA synthesis). This explicitly supports CGRs altering hormonal balances and impacting resource allocation for tuber development.

Claim 3.3: The physiological age of the cutting material (juvenility) can also influence its capacity for tuber formation.

Konishi, K., & Inaba, K. (1967). Studies on flowering control of dahlia. VII On dormancy of crown-tuber. Journal of the Japanese Society for Horticultural Science, 36(1), 131-140. (Author’s note: Written in Japanese. English translation provided by Gemini AI and verified by ChatGPT 4o.)

The "Summary" states that "Crown-tubers obtained from the plants which were propagated from cuttings after June rested weaker than those obtained from the mother plants". It also notes that "The earlier the cutting time, the deeper [the] rest of crown-tuber". This demonstrates that the timing of propagation (and implicitly the physiological age of the cutting/resulting plant) influences the dormancy characteristics of the resulting tubers.

TUCHIYA, S. (1993). Studies on the Production of Tuberous Roots in Dahlia . Special bulletin of Ishikawa Agricultural College, 18, 70-73.

Chapter 2 discusses the "cultivation using the cuttings" and how "the weight of the tuberous roots formed per plant decreased as the time of cutting was delayed", implying an optimal physiological state or timing for the cutting itself.

The article mentions that "In single node cuttings, taken from various sites along the branch, tuberization ability increased with proximity to the base of the branch, where axillary buds are more inhibited". This directly indicates that the position (and thus implied physiological age/developmental stage) of the cutting influences its tuberization ability.

Hetman, J., Łukawska-Sudoł, S., Pudelska, K., & Parzymies, M. (2017). The effect of the cutting method on rooting of Dahlia pinnata Cav. cuttings . Acta Scientiarum Polonorum Hortorum Cultus, 16(2), 149-160.

The study investigates the "quality of soft cuttings" based on six different "types of cuttings" (e.g., 'with heel', 'without heel', tip, long tip, lateral, middle). It states that "The best quality rooted cuttings, in terms of a fresh weight, number of leaves and a fresh weight and number of roots, were the heel cuttings". The discussion further notes that "a cultivar and a type of cuttings decided about the number of rooted cuttings of dahlia, while the morphological features depended on a type of cuttings". This directly relates the type and quality of cutting (influenced by physiological state) to rooting and subsequent plant vigor.

Pudelska, K., Hetman, J., Łukawska-Sudoł, S., & Parzymies, M. (2015). The efficiency of mother crowns and quality of soft cuttings of a few dahlia cultivars. Acta Scientiarum Polonorum Hortorum Cultus, 14(6), 189-200.

While the article doesn't explicitly use the term "juvenility," it heavily focuses on the "quality of soft cuttings" and their rooting efficiency based on "a type of cuttings" (e.g., apical vs. 'with heel' vs. 2-node) and the "mother crown efficiency" (number of sprouts appearing in spring and their timing for excision). The overall research aims to evaluate "if soft cuttings snipped off from different parts of shoots are a valuable plant material for propagation", implying that the nature of the cutting material itself is a factor in successful propagation outcomes.

Legnani, G., & Miller, W. B. (2001). Using photoperiod to manipulate flowering and tuberous root formation in seed Dahlias . Greenh. Prod. New, 11(13), 36-40.

The article discusses various photoperiod schedules for "plug production" and "after transplanting," and mentions the timing of "seedlings [becoming] established enough for overhead watering", implying that the plant's stage of development (physiological age) is considered in relation to treatment effects on tuber formation.

Menzel, C. M. (1985). The control of storage organ formation in potato and other species: a review. Part 2.

The review discusses how "seed tubers of potato which have been stored for long periods at warm temperatures in the dark ('physiologically old')" tend to produce sprouts with premature tuberization. It also mentions "single-leaf cuttings" and "isolated potato sprouts" in studies, implying that the physiological state of the propagule affects its tuberization response.

CANTOR, M., BUTA, E., GOCAN, T., & CRIŞAN, I. (2016). Influence of Cultivar and Planting Material on Soluble Dry Matter Content of Dahlia Tuberous Roots . Bulletin of the University of Agricultural Sciences & Veterinary Medicine Cluj-Napoca. Horticulture, 73(2). Abstract only accessed. Academic Paywall.

The study investigated the influence of "planting material (forced and unforced tuberous roots)" on soluble dry matter content of dahlia tubers. The conclusion states that "the forcing of the tuberous roots affected the accumulation of soluble dry matter content at dahlia tubers", indicating that the treatment/method of producing the planting material influences tuber characteristics.

Biran, I., & Halevy, A. H. (1973). The relationship between rooting of Dahlia cuttings and the presence and type of bud . Physiologia Plantarum, 28(2), 244-247. Abstract only accessed. Academic Paywall.

The abstract states that "Dahlia cuttings with actively growing buds are relatively hard to root as compared with those having non-growing or inhibited buds". It also notes that "In cuttings containing buds which sprouted during the rooting period, an inverse relationship was found between rooting percentage and growth rate of buds". This indicates that the physiological state or activity level of buds on the cutting material directly influences its rooting capacity.

The study analyzes the rooting potential of "type of cuttings" (with heel, without heel, softwood cuttings excised from tuberous shoots). It specifically notes that "The Dahlia softwood cuttings excised from tuberous shoots yielded better rooting when treated with IBA", indicating that the type or source of cutting material (reflecting physiological state) influences rooting success.

Fatima, B., Usman, M., Ashraf, T., Waseem, R., & Ali, M. A. (2007). In vitro shoot regeneration from cotyledon and hypocotyl explants of dahlia cultivars . Pak. J. Agri. Sci, 44(2), 312-316.

The study investigates different "explant types" (cotyledon leaf and hypocotyl) used as starting material for dahlia micropropagation. It found that the "shoot tip was significantly superior on a hypocotyl as it gave the highest response to shoots formation", indicating that the type or source of plant material (reflecting its physiological state/origin) significantly influences its regeneration capacity and growth in vitro.

Ibrahim, M. A., & Daraj, I. A. (2015). Micropropagation of dahlia plants Dahlia variabilis Wild (Desf.). Effect of explant and plant growth regulators on shoot regeneration and growth . Advances in Agriculture & Botanics, 7(1), 1-6.

The study investigates the effect of "explant type on shoot regeneration" (cotyledon, hypocotyl, shoot tip, nodal, root segment) in dahlia micropropagation. The results show that the "shoot tip was significantly superior on a hypocotyl as it gave the highest response to shoots formation" (86.67% vs. 43.33%). This directly supports that the type of explant (reflecting physiological origin/age) influences its regeneration capacity, a key factor in successful propagation.

Claim 3.4: Practices like taking cuttings too late in the season, when mother plants are already signaling tuberization, can improve tuber yield from cuttings.

Zimmerman, P. W., & Hitchcock, A. E. (1929). Root formation and flowering of dahlia cuttings when subjected to different day lengths . Botanical Gazette, 87(1), 1-13.

The article observes that "Cuttings taken in late September and October produce storage roots at the sacrifice of fibrous roots, and flower when only a few inches high". It also notes that "Cuttings taken from October 15 to October 28 developed storage roots, as a rule, instead of the normal fibrous roots characteristic for early cuttings". This indicates a strong tendency for storage root formation in later-season cuttings, suggesting an improvement in tuber yield from those cuttings.

The research's primary aim is to "assess the impact of planting dates on tuber production" using rooted cuttings. It evaluates three planting dates (September 15th, October 15th, and November 15th) and concludes that "October 15th was found to be [the] most suitable month of planting as interpreted from overall performance in terms of tuber production and characteristics". This directly supports the idea that the timing of planting (a propagation practice for cuttings) influences tuber yield.

TUCHIYA, S. (1993). Studies on the Production of Tuberous Roots in Dahlia . Special bulletin of Ishikawa Agricultural College, 18, 70-73.

The article states "the weight of the tuberous roots formed per plant decreased as the time of cutting was delayed", indicating that earlier cutting (within an optimal window) is beneficial, which relates to the physiological state influenced by mother plant signals.

Pudelska, K., Hetman, J., Łukawska-Sudoł, S., & Parzymies, M. (2015). The efficiency of mother crowns and quality of soft cuttings of a few dahlia cultivars . Acta Scientiarum Polonorum Hortorum Cultus, 14(6), 189-200.

The article evaluates the efficiency of mother crowns for producing shoots suitable for cuttings from "the 10th of February till the 20th of April", focusing on early spring production. It discusses how "a cultivar and a season were the factors deciding about the number of soft stems sprouting from a mother plant and then used for cuttings", implying that timing impacts the quantity and quality of cuttings produced, which in turn affects propagation success.

The article discusses the timing of cutting excision, stating that "The cuttings were taken between March 10-12th and April 20th". It emphasizes the importance of obtaining the "highest possible number of soft stems that might be used as a source of cuttings". The findings indicate that different cutting types, taken within this spring period, can enhance propagation effectiveness and produce good quality rooted plants, linking cultivation timing to propagation success, which ultimately influences yield.

Menzel, C. M. (1985). The control of storage organ formation in potato and other species: a review. Part 2.

The review discusses studies on potato cuttings and their tuberization response to photoperiod, aligning with the idea that the timing of cutting (and thus the mother plant's physiological state/tuberization signaling) can affect the cuttings' tuber development.

The article, in its "Conclusions" and "Results and discussion" sections, explicitly identifies "planting date" as a "management practice that can help farmers to protect dahlia flowers from heat stress". It advises: "planting dahlia early in Spring will provide harvesting starting when temperatures still are not very high, thus avoiding injury by heat. A second planting can be performed in late Summer, so that [the] reproductive phase starts when temperatures are dropping in early Fall, thus also avoiding high temperatures". This directly links specific planting dates to successful plant performance in relation to environmental conditions, thereby influencing overall yield and quality.

From Part 4: Disrupted Tuber Formation: What’s Really Going On?

Claim 4.1: Commercial growth regulators (CGRs) are used to manipulate plant architecture (e.g., height, branching) and flowering time for market purposes, which can have downstream effects on tuber formation.

Read, P. E., Dunham, C. W., & Fieldhouse, D. J. (1972). Increasing Tuberous Root Production in Dahlia pinnata Cav. with SADH and Chlormequat1 . HortScience, 7(1), 62-63.

The study directly investigates the use of SADH and chlormequat (CGRs) to "Increase Tuberous Root Production in Dahlia pinnata Cav." and reports successful manipulation. It notes "Only slight growth retardation was observed during the early part of the growing period, along with slightly darker green color," demonstrating an effect on vegetative growth.

The study's introduction and objectives directly state its aim to "evaluate the effect of selected growth retardants [CCC, Alar, Ethrel] on growth, flowering, vase-life, and tuber formation of dahlia". The results consistently show that CCC and Alar significantly reduced plant height and promoted branching, directly demonstrating manipulation of plant architecture. Early bud initiation and flowering were also observed with CCC and Alar. The conclusion explicitly states Alar is "ideal for commercial cut flower production and propagation" due to enhanced flower quality and tuber yield.

The study explicitly aims to determine the role of gibberellic acid (GA3) and salicylic acid (SA) (both CGRs) in "improving marketable quality, increasing yield and vase life of dahlia". Its findings demonstrate that GA3 treatments resulted in the tallest plants (118.43 cm), significantly increased branching and leaf numbers, directly manipulating plant architecture. SNP treatments also significantly hastened flowering time (GA3 200 ppm gave most rapid flowering at 39.57 days). The study also explicitly measures and finds significant increases in "tuber length, and numbers/plant" and "tuber fresh weights and their number/Plant" due to these treatments, confirming downstream effects on tuber formation.

Chauhan, C., Kumar, M., Malik, S., Yadav, M. K., Gangwar, L. K., & Tomar, A. (2022). Effect of exogenous application of Sodium Nitroprusside (SNP) and Gibberellic Acid (GA3) on growth and flowering of Dahlia (Dahlia variabilis L.) CV. Kenya .

The study directly investigates the effect of Gibberellic Acid (GA3) and Sodium Nitroprusside (SNP) , which are considered plant growth regulators. Findings show that GA3 @ 200 ppm significantly increased plant height (118.06 cm), plant spread (85.23 cm), and number of branches (10.95 primary, 9.00 secondary), directly demonstrating manipulation of plant architecture. SNP @ 200 ppm treatments resulted in earlier flower bud appearance (65.93 days) and 50% flowering (70.63 days), showing influence on flowering time. The study also explicitly measures "number of tubers per plant" and "fresh weight of tubers per plant" as parameters affected by these growth regulators, demonstrating downstream effects on tuber formation.

Halevy, A. H., & Biran, I. (1974, April). Hormonal regulation of tuberization in Dahlia . In II International Symposium on Flower Bulbs 47 (pp. 319-330). Abstract only accessed. Academic Paywall.

The abstract reports that "SADH and ethephon promoted the tuberization in whole dahlia plants". As SADH and ethephon are CGRs, this demonstrates their use in manipulating plant development (tuberization).

The abstract discusses the application of abscisic acid (ABA), succinic acid-2,2-dimethylhydrazide (SADH), and 2-chlorethyl phosphonic acid (ethephon), which are all types of CGRs. It states these treatments "promoted the tuberization of dahlia plants", directly indicating their use in manipulating plant development (tuberization).

Malik, S. A., Rather, Z. A., Wani, M. A., Din, A., & Nazki, I. T. (2017). Effect of growth regulators on plant growth and flowering in dahlia (Dahlia variabilis) cv. Charmit . Journal of Experimental Agriculture International, 15(3), 1-7.

The study directly investigates the effects of various growth regulators (Ethephon, Alar, and Maleic hydrazide – all CGRs) on dahlia 'Charmit'. Its findings demonstrate that these growth regulators significantly reduce plant height, with MH 1000 ppm causing the maximum reduction. They also notably increase the number of primary and secondary branches, and overall leaf count and stem diameter, particularly with MH at 1000 ppm. Furthermore, the study observed that these CGRs delayed flower bud appearance and color break, but generally increased the number and diameter of flowers. This clearly demonstrates their use in manipulating plant architecture and influencing flowering characteristics.

Phetpradap, S., Hampton, J. G., & Hill, M. J. (1994). Effect of hand pinching and plant growth regulators on seed production of field grown hybrid dahlia . New Zealand journal of crop and horticultural science, 22(3), 313-320.

The study investigates the effects of CGRs (paclobutrazol and chlormequat chloride) on dahlia. The abstract states that "PGR-treated plants reached the same stages 1 or 2 days earlier than the control, but these differences were not significant" for first flowering, but it found that "pinching reduced... the spread of flowering by 14 days". It also notes that "paclobutrazol reduced... plant height and main stem length", demonstrating manipulation of plant architecture. The introduction states that chemical manipulation aims "to suppress vegetative growth, reduce plant height, alter plant shape, size, and form, and promote flower initiation and uniformity".

Khan, F. U., & Tewari, G. N. (2003). Effect of growth regulators on growth and flowering of dahlia (Dahlia variabilis L.) . Indian Journal of Horticulture, 60(2), 192-194.

The study directly investigates the effect of gibberellic acid (GA) and chlormequat (CCC), both types of CGRs, on dahlia. Its findings demonstrate that CCC significantly reduced plant height (e.g., by 15.93 cm at 6000 ppm) and increased the number of branches (up to 7.98) and leaves, directly showing manipulation of plant architecture. The study also found that CCC markedly hastened the period of full bloom (earliest at 83.0 days with 6000 ppm CCC), while GA treatments delayed flowering, showing influence on flowering time.

Mills-Ibibofori, T., Dunn, B. L., Maness, N., & Payton, M. (2019). Effect of LED lighting and gibberellic acid supplementation on potted ornamentals . Horticulturae, 5(3), 51.

The study directly investigates the effect of LED lighting (a tool for manipulating environmental conditions) and gibberellic acid (GA3) (a CGR) on dahlia. Its findings show that GA3 applications significantly increased dahlia plant height, demonstrating manipulation of plant architecture. The study also found a significant interaction of light with GA3 influencing mean flower number, showing an influence on flowering. These manipulations of overall plant growth and flowering can have downstream effects on processes like tuber formation.

Menzel, C. M. (1985). The control of storage organ formation in potato and other species: a review. Part 2.

The review frequently discusses the use of "growth retardants such as CCC and SADH" (CGRs) and their effects, noting they "inhibit endogenous gibberellin synthesis and reduce gibberellin levels", and can "restrict stem elongation". It explicitly mentions their use to "promote storage-organ formation".

Gavinlertvatana, P., Read, P. E., Wilkins, H. F., & Heins, R. (1979). Influence of photoperiod and daminozide stock plant pretreatments on ethylene and CO2 levels and callus formation from dahlia leaf segment cultures . J. Am. Soc. Hortic. Sci, 104, 849-852.

This study investigates the effects of daminozide (a CGR) pretreatments on dahlia stock plants. The discussion notes that daminozide "inhibits shoot growth", demonstrating its ability to manipulate plant growth parameters like height. It further states that "stock plant manipulation can modify relative rate of C2H4 and CO2 emanation, thus resulting in profound physiological responses of tissues in cultures," which implies downstream effects on plant development.

Pal, S. L. (2019). Role of plant growth regulators in floriculture: An overview . J. Pharmacogn. Phytochem, 8, 789-796.

As an overview of PGRs, the article states that they "are being used by the commercial growers of ornamental plants as a part of cultural practice" and have a "quicker impact on vegetative as well as flower yield of flowering crops". It explicitly mentions their use to "control plant habit, branching and flowering" and "improve height and yield", which directly relates to manipulating plant architecture and influencing flowering for commercial purposes.

Kumar, T., Rinu, R. S., & Praddyum, S. T. A comprehensive review of Plant Growth Regulators (PGRs) and their impact on flowering and ornamental crops with insights into effective application methods.

As a comprehensive review of Plant Growth Regulators (PGRs), the article explicitly states that PGRs "offer valuable tools for growers to manipulate plant architecture, flowering, and overall crop yield and quality". It details how PGRs can be strategically utilized to "control plant architecture, promote branching, regulate flowering time, and enhance flower size, color, and longevity", confirming their role in manipulating plant characteristics for commercial purposes.

Claim 4.2: Specific CGRs like Ethephon, Daminozide (Alar), SADH, and Maleic Hydrazide (MH) impact plant growth by altering hormonal balances, potentially affecting resource allocation for tuber development.

The thesis specifically investigates the effects of Alar (Daminozide), CCC (Chlormequat chloride), and Ethrel (Ethephon). The results show Alar significantly enhanced "tuber fresh weight" and "dry weight". CCC also "promoted tuber yield". Ethrel treatments "negatively impacted tuber mass" and showed "inhibitory effects on tuber formation". These findings demonstrate that specific growth retardants (CGRs) directly affect tuber formation and growth, and the rationale explicitly links CCC/Alar's effect on height to "inhibition of cell elongation and reduction in gibberellin synthesis".

Read, P. E., Dunham, C. W., & Fieldhouse, D. J. (1972). Increasing Tuberous Root Production in Dahlia pinnata Cav. with SADH and Chlormequat1 . HortScience, 7(1), 62-63.

The article directly demonstrates that foliar sprays of SADH (succinic acid-2,2 dimethylhydrazide) and chlormequat increased the number and size of tuberous roots, and frequently tripled root weight. It states that these "growth retardants were able to alter the plants' tuberous root responses to photoperiodic stimuli," explicitly showing CGRs affecting resource allocation and tuber development.

The article directly tests Gibberellic Acid (GA3) and Salicylic Acid (SA) on dahlia plants. GA3 is a gibberellin, a plant hormone. The study's results show that both GA3 and SA significantly increased tuber length, number of tubers per plant, and fresh and dry weight of tubers. The article explicitly refers to GA3 and SA as "growth regulators" that "play a great role in enhancing growth, flowering and yield of dahlia plants". This demonstrates that these specific CGRs impact plant growth and directly affect tuber development and resource allocation.

The article directly tests Gibberellic Acid (GA3) and Sodium Nitroprusside (SNP), stating their effects on plant growth, flowering, and tuber production in dahlia. GA3 is a known gibberellin, a plant hormone. The study found that GA3 @ 200 ppm significantly increased the number of tubers per plant (12.43) and fresh weight of tubers per plant (168.03 g). The study's conclusion highlights that the application of both SNP and GA3 "was found suitable for improving growth and flowering parameters and tuber yield of Dahlia". This demonstrates that specific PGRs impact plant growth and directly affect tuber development/resource allocation.

Khan, F. U., & Tewari, G. N. (2003). Effect of growth regulators on growth and flowering of dahlia (Dahlia variabilis L.) . Indian Journal of Horticulture, 60(2), 192-194.

The article directly tests gibberellic acid (GA) and chlormequat (CCC), which impact plant growth. It explicitly states that the "Decrease in plant height by the growth regulators is due to inhibition of gibberellin biosynthesis which results in cell elongation". It also notes that increases in plant height by GA are due to "hyper-elongation in stem and internode". These findings demonstrate that these specific CGRs alter growth processes by affecting cellular activities, thus impacting plant growth.

Malik, S. A., Rather, Z. A., Wani, M. A., Din, A., & Nazki, I. T. (2017). https://www.cabidigitallibrary.org/doi/full/10.5555/20063048282 . Journal of Experimental Agriculture International, 15(3), 1-7.

The article directly tests Ethephon, Alar (Daminozide), and Maleic hydrazide (MH). It explicitly states that the "Decrease in plant height by the growth regulators is due to inhibition of gibberellin biosynthesis". It also notes that growth regulators increase branching by "suppression of apical dominance thereby diverting the polar transport of auxins towards the basal buds". These findings demonstrate that these specific CGRs alter hormonal balances and directly impact plant growth.

The research directly demonstrates that daminozide sprayed on stock plants promoted callus formation, and C2H4 and CO2 production. The discussion section explicitly links increased C2H4 levels to daminozide, notes that daminozide "has been proposed to interfere with auxin synthesis... or auxin transport," and suggests its effect "may be exerted through increased ethylene production," directly indicating its impact on plant growth and alteration of hormonal balances.

Menzel, C. M. (1985). The control of storage organ formation in potato and other species: a review. Part 2.

The review extensively details the effects of SADH (N-dimethylaminosuccinamic acid) and CCC (chlormequat) on various species (including dahlia), stating they "inhibit endogenous gibberellin synthesis" and promote tuberization. It also discusses the mixed effects of ethylene (via CEPA) on tuberization and its influence on hormonal balance (e.g., C2H4 inhibiting root development which is a site of GA synthesis).

Halevy, A. H., & Biran, I. (1974, April). Hormonal regulation of tuberization in Dahlia . In II International Symposium on Flower Bulbs 47 (pp. 319-330). Abstract only accessed. Academic Paywall.

The abstract directly discusses the effects of SADH and ethephon, stating they "promoted… tuberization in whole dahlia plants". It also notes that ABA enhanced tuberization and GA inhibited it. It proposes that "Ethylene may have a different effect at different stages of development, promoting the initiation of tuberization and inhibiting the later stages of tuber filling", directly linking these growth regulators and hormones to tuber development and resource allocation.

The abstract directly names and investigates SADH and ethephon, stating that they "promoted the tuberization of dahlia plants" and that gibberellic acid (GA) "inhibited tuberization". It also notes that "Evolution of endogenous ethylene reached a peak... after the start of short-day treatments... one week before the onset of tuberization", demonstrating the interplay of endogenous hormones (ethylene) with tuberization.

The article directly tests paclobutrazol and chlormequat chloride (which are CGRs). The abstract reports that "Seed yield per plant was significantly increased following the application of chlormequat chloride... and by paclobutrazol". It also explicitly mentions that these PGRs "suppress vegetative growth" and "reduce plant height", which are direct impacts on plant growth.

Mills-Ibibofori, T., Dunn, B. L., Maness, N., & Payton, M. (2019). Effect of LED lighting and gibberellic acid supplementation on potted ornamentals . Horticulturae, 5(3), 51.

The article directly investigates gibberellic acid (GA3), a plant growth regulator and a type of gibberellin. Its findings demonstrate that GA3 supplementation significantly increased dahlia plant height and influenced flower number, directly showing its impact on plant growth by altering hormonal effects.

Pal, S. L. (2019). Role of plant growth regulators in floriculture: An overview . J. Pharmacogn. Phytochem, 8, 789-796.

The article provides an overview of various types of plant growth regulators including Auxins, Gibberellins, Cytokinins, Abscisic acid (ABA) and Ethylene. It describes their distinct physiological activities, such as Gibberellins promoting stem elongation, Auxins promoting root initiation, and ABA inducing dormancy. This confirms that specific CGRs (which mimic or interfere with these hormones) impact plant growth by altering hormonal balances.

Kumar, T., Rinu, R. S., & Praddyum, S. T. A comprehensive review of Plant Growth Regulators (PGRs) and their impact on flowering and ornamental crops with insights into effective application methods.

The article extensively reviews various types of Plant Growth Regulators, including Auxins, Gibberellins, Cytokinins, Abscisic Acid, and Ethylene. It describes their specific physiological mechanisms of action on plant growth and development (e.g., Gibberellins promote stem elongation, Auxins promote root initiation, Ethylene regulates senescence), thereby supporting that CGRs (which interact with these hormones) impact plant growth by altering hormonal balances.

Fatima, B., Usman, M., Ashraf, T., Waseem, R., & Ali, M. A. (2007). In vitro shoot regeneration from cotyledon and hypocotyl explants of dahlia cultivars . Pak. J. Agri. Sci, 44(2), 312-316.

The study investigates the effect of NAA (naphthalene acetic acid) and BA (6-benzyl amino purine), which are plant growth regulators/hormones, on shoot regeneration in dahlia explants. It found that specific combinations and concentrations of these PGRs (e.g., NAA and BA at 3 mg/L each) produced "Maximum response for callus induction... and shoot regeneration", directly demonstrating that these substances impact plant growth and developmental processes in vitro.

Claim 4.3: Dahlias purchased as potted plants from garden centers may have been treated with CGRs, which can alter their initial growth habit and potentially delay or reduce tuberization compared to tubers grown for propagation.

Mills-Ibibofori, T., Dunn, B. L., Maness, N., & Payton, M. (2019). Effect of LED lighting and gibberellic acid supplementation on potted ornamentals . Horticulturae, 5(3), 51.

The study directly investigates the effect of LED lighting (a tool for manipulating environmental conditions) and gibberellic acid (GA3) (a CGR) on dahlia. Its findings show that GA3 applications significantly increased dahlia plant height, demonstrating manipulation of plant architecture. The study also found a significant interaction of light with GA3 influencing mean flower number, showing an influence on flowering. These manipulations of overall plant growth and flowering can have downstream effects on processes like tuber formation. The title "Effect of LED lighting and gibberellic acid supplementation on potted ornamentals " directly places it in the context of potted plants.

Ali, E. O. H. (2004). Pathological studies on dahlia tuber rots (Doctoral dissertation, Department of Agricultural Botany, Faculty of Agriculture at Moshtohor, Zagazig University).

While the thesis doesn't focus on CGRs, its introduction describes dahlia propagation, noting "Large number of stem cuttings can be taken from dahlia tubers where, they rooted easily in greenhouse then planted normally in roundly form into pot or planted in the field in rows". This indicates common commercial practices for potted dahlias. The primary focus of the thesis is on fungal and bacterial diseases affecting dahlias in the field, storage, and during propagation, including "rotted dahlia tubers". The study details the identification of various pathogens (e.g., Sclerotium rolfsii, Fusarium solani, Erwinia carotovora) that attack dahlia tubers, causing rot and destruction. This highlights a significant factor that can "disrupt tuberization" by destroying tubers.

Pal, S. L. (2019). Role of plant growth regulators in floriculture: An overview . J. Pharmacogn. Phytochem, 8, 789-796.

Kumar, T., Rinu, R. S., & Praddyum, S. T. A comprehensive review of Plant Growth Regulators (PGRs) and their impact on flowering and ornamental crops with insights into effective application methods.

The author’s personal observation that potted dahlias sold as flowering annuals in retail stores show a markedly different growth habit than potted dahlias grown from tubers. In his experience, potted store-bought dahlias typically do not produce significant tubers during their first year. Whether these phenotypical traits are caused by CGRs or by growing conditions typical in mass production of dahlias, the author cannot say with ceertainty.

From Part 5: Are Tuber Traits Genetic?

Claim 5.1: Tuber formation in dahlias is a polygenic trait, meaning it is influenced by multiple interacting genes rather than a single gene.

Hegde, B. N., Shirol, A. M., Harshavardhan, M., & Kumar, P. P. Genetic Divergence Analysis of Dahlia (Dahlia variabilis L.) Genotypes .

The study investigates "genetic variability, heritability, genetic advance and genetic divergence" among 35 dahlia genotypes using 20 characters. It states that "The analysis of variance permits estimation of phenotypic and genotypic coefficients of variability of various polygenic traits", and that "All the characters (except plant spread and width of the tuber) showed high heritability along with higher or moderate genotypic coefficient of variation and genetic advance indicating that most likely the heritability was due to additive gene effects". This directly supports that dahlia traits are polygenic and influenced by multiple genes.

Pal, A., Rilkotia, P., & Bhuj, B. D. (2024). Studies on genetic variability, heritability, genetic advance, correlation and path analysis in dahlia (Dahlia variabilis L.) under tarai region of Uttarakhand . Journal of Natural Resource Conservation and Management, 5(2), 137-144.

The article discusses "genetic variability," "heritability," and "genetic advance" for 15 quantitative characters in dahlias, stating that "The phenotypic character of the plant is governed by genotype and environment interaction". It reports that "high P.C.V and G.C.V values indicates the high variability among the characters due to genetic factor[s]", supporting the general concept of complex genetic control for traits, which is characteristic of polygenic inheritance, even if not explicitly using "polygenic" for tuber formation specifically.

Menzel, C. M. (1985). The control of storage organ formation in potato and other species: a review. Part 2.

As a comprehensive review, it discusses the complex control of storage organ formation, which by its nature implies multi-gene involvement for such a physiological process, although it doesn't explicitly use the term "polygenic" for dahlia. It implicitly supports this through the wide range of species and responses discussed.

Claim 5.2: Different dahlia cultivars exhibit varying tendencies for tuber size, shape, eye formation, and storability, even under ideal conditions, due to genetic differences.

Hegde, B. N., Shirol, A. M., Harshavardhan, M., & Kumar, P. P. Genetic Divergence Analysis of Dahlia (Dahlia variabilis L.) Genotypes .

The study directly assesses "35 dahlia (Dahlia variabilis L.) genotypes" for genetic variability and divergence across 20 characters, including "Length of tuber (mm)", "Width of tuber (mm)", "Individual tuber weight (g)", and "Number of tubers per plant". It found "highly significant" differences for all 20 characters among genotypes, and specific cluster means showing variations in tuber length, width, and weight among different groups of genotypes. The article concludes that "The improvement in these characters through direct selection to develop better cultivars of dahlia can easily be done". This explicitly supports that different cultivars exhibit varying tendencies for tuber size, shape, and quantity due to genetic differences.

The study directly evaluates five different dahlia cultivars ('Anarkali', 'Gargi', 'Giani Zail Singh', 'Matungini' and 'Suryadev') for tuber production characteristics. It found that "Anarkali demonstrated superior performance in tuber weight... and tuber yield per plot", while "Matungini excelled in the number of tubers per plant... tuber length... and tuber diameter", and "Giani Zail Singh showcased the best tuber diameter". The discussion section notes, "Differences in tuber output among cultivars are due to their capacity to respond to environmental circumstances, which affects tuber development", and that "Genetic variances... may influence changes in tuber weight". This clearly supports cultivar-specific genetic differences affecting tuber traits.

Konishi, K., & Inaba, K. (1967). Studies on flowering control of dahlia. VII On dormancy of crown-tuber . Journal of the Japanese Society for Horticultural Science, 36(1), 131-140. (Author’s note: Written in Japanese. English translation provided by Gemini AI and verified by ChatGPT 4o.)

The Summary states that "The degree of rest in dahlia crown-tuber varied among the varieties". It categorizes varieties into three types based on sprouting percentage and subsequent growth (from all crown-tubers sprouting well to none sprouting at all). The "IV. Discussion" section further elaborates that "The degree of dormancy varied among varieties". This directly supports cultivar-specific differences in dormancy, which affects storability and regrowth.

The study directly investigates two dahlia cultivars ('Kennemerland' and 'Red Pygmy') and assesses the "influence of storage conditions on the morphology and biochemical composition of Dahlia tubers". It explicitly states that "the inulin accumulation inside the tubers... depends on the cultivar type" and that "the polyacetylene concentration increase... is dependent on the cultivar type". Furthermore, the biometric parameters and FT-IR/FT-Raman analyses show cultivar-specific responses to storage substrates in terms of root weight loss and biochemical changes.

Zimmerman, P. W., & Hitchcock, A. E. (1929). Root formation and flowering of dahlia cuttings when subjected to different day lengths . Botanical Gazette, 87(1), 1-13.

The study noted cultivar-specific responses, stating that "The short-day condition stimulated tuberous root formation in some of the varieties examined, but did not in others". It also observed different responses in flowering behavior to day length across varieties (some flowered only on short days, others independently of day length) , and even different storage root shapes (short and rounded like potato tubers in short days vs. slender with long necks for normal day plants).

TUCHIYA, S. (1993). Studies on the Production of Tuberous Roots in Dahlia . Special bulletin of Ishikawa Agricultural College, 18, 70-73.

The article notes that "The short-day condition stimulated tuberous root formation in some of the varieties examined, but did not in others", showing cultivar-specific responses to environmental cues for tuberization. It also mentions variations in harvested tuber weight range.

Schneck, K. K., Boyer, C. R., & Miller, C. T. (2021). Supraoptimal Root-zone Temperatures Affect Dahlia Growth and Development . HortTechnology, 31(6), 667-678.

The study was conducted on "seven dahlia cultivars" from different series (Dalaya, XXL, Melody) to evaluate the effects of supraoptimal RZTs on their growth and development. The results explicitly show inconsistent reactions to supraoptimal RZTs among different cultivars, with some showing more adaptability or recovery than others. For example, the Dalaya series generally developed poor, or low-vigor root growth compared with the XXL series, and different cultivars showed varied responses in root rating, plant height, and flower development to the various temperature treatments. This directly supports the idea of cultivar-specific differences in response to environmental conditions.

The article states that "The inulin quantity in plants varies with species, natural conditions, and maintenance". It also refers to previous studies indicating "considerable variability observed among cultivars" in chemical composition like carbohydrates, fiber, and proteins in dahlia tubers. This directly supports cultivar-specific differences in tuber composition influenced by genetic factors.

Ivanova, V., & Zaprjanova, N. (2020). Study on phenological behaviours of Dahlia variabilis Hort. in overwintering of tuberous roots in the soil .

The study directly investigates three different dahlia cultivars ('Vitus', 'White Ball', 'Dark Red') to determine "damage or lack thereof in overwintering the tuberous roots in the soil". The results show significant cultivar-specific differences in phenological behaviors, including emergence timing, growth rate, and flowering duration, under overwintering conditions (e.g., 'Dark Red' emerged earliest, 'Vitus' had longest flowering duration). This supports that different cultivars have varying inherent responses.

The abstract states that the accumulation of soluble dry matter content in dahlia tubers "depends on the cultivar". It provides specific data showing varying soluble dry matter content among seven different dahlia cultivars, directly supporting that cultivars differ in their tuber composition.

The study was conducted using "a single strain and also var. Tensin (medium decorative)", implicitly acknowledging cultivar differences, although its primary focus is on anatomical observation rather than comparative cultivar performance. The very act of choosing a specific variety ('Tensin') for observation implies that varietal differences exist in their formation.

Menzel, C. M. (1985). The control of storage organ formation in potato and other species: a review. Part 2.

The review frequently mentions "species and cultivars" responding differently to environmental or hormonal treatments, for example, "In most species and cultivars so far examined" and discussing differences in cultivar heat tolerance or gibberellin activity. Table 4 lists "Dahlia variabilis" as a species where GA reduces or delays tuber formation, implying its specific response.

The study directly evaluates "eleven genotypes of dahlia" and finds "significant differences among the genotypes for all the fifteen characters studied". It reports "high variability among the characters due to genetic factor[s]", clearly supporting cultivar-specific variations in traits, attributable to genetics.

Claim 5.3: Breeders can select for tuber-forming traits through seedling selection over generations.

Hegde, B. N., Shirol, A. M., Harshavardhan, M., & Kumar, P. P. Genetic Divergence Analysis of Dahlia (Dahlia variabilis L.) Genotypes .

The study investigates "genetic variability, heritability, genetic advance and genetic divergence" in dahlia genotypes to aid breeding programs. It concludes that traits showing "high heritability along with higher or moderate genotypic coefficient of variation and genetic advance indicating that most likely the heritability was due to additive gene effects" are useful for "efficient improvement of a character through simple selection". It also states that "The genotype from individual cluster[s] can be utilized in the selection/breeding programme for desirable economic characters in dahlia". This directly supports that breeders can select for tuber-forming traits through a selection process based on genetic parameters.

The article's introduction states that "The wide diversity leads to a lot of scope for improving these traits through breeding as this rich pool of diversity furnish[es] the resource for incessant selection of adapted genotypes". The results discuss "heritability" and "genetic advance" and conclude that "the traits which showed high genetic gain were also coupled with high heritability and provides a good scope for selection. Therefore, direct selection for these characters will have a positive impact on [the] number of flowers per plant". This directly supports the principle of selection for desirable traits in breeding programs.

Menzel, C. M. (1985). The control of storage organ formation in potato and other species: a review. Part 2.

As a review on "control of storage organ formation," it discusses how understanding these physiological controls can inform manipulation for desired outcomes, including breeding for adapted cultivars (e.g., "heat-tolerant potato cultivars may have the ability to inactivate gibberellin"), which is a direct application of understanding genetic variation for breeding purposes.

From Part 6: The Science of Better Tuber Harvests

Claim 6.1: Cool, moist soil and shortening daylength are key triggers for robust tuber formation.

Brøndum, J. J., & Heins, R. D. (1993). Modeling temperature and photoperiod effects on growth and development of dahlia . JOURNAL-AMERICAN SOCIETY FOR HORTICULTURAL SCIENCE, 118, 36-36.

The study's results on tuberous root weight indicate that tuberous roots formed on plants in 10 and 12-hour photoperiod treatments at 15 and 20C, whereas no tuberous roots formed at 25 and 30C regardless of photoperiod, showing that longer photoperiods suppress tuber formation. The "Discussion" section explicitly states that "Low temperature and SD promoted tuberous root formation" and specifically notes that "15C promotes tuberous root formation".

Legnani, G., & Miller, W. B. (2000). Night Interruption Lighting Is Beneficial in the Production of Plugs of Dahlia Sunny Rose' . HortScience, 35(7), 1244-1246.

The study demonstrates that "SD [short day] increased tuberous root development" and produced "large, rounded, tuberous roots" compared to LD which produced "slender, elongated structures". This directly supports that shortening daylength triggers robust tuber formation.

Zimmerman, P. W., & Hitchcock, A. E. (1929). Root formation and flowering of dahlia cuttings when subjected to different day lengths . Botanical Gazette, 87(1), 1-13.

The article consistently links "heavy root storage" with "short day" conditions.

The "Summary" explicitly states that "The short day treatment (8-hour photoperiod for 20 or 40 days)... increased the diameters of roots", directly linking shortening daylength (short-day treatment) to robust root (tuber) formation. The "V. Summary" section also notes, "The growth of shoot was inhibited under the day-length shorter than 12 hours, while it was enhanced under that longer than 13 hours." This supports the conditions for robust tuber formation.

TUCHIYA, S. (1993). Studies on the Production of Tuberous Roots in Dahlia . Special bulletin of Ishikawa Agricultural College, 18, 70-73.

The article states that "short-day condition stimulated tuberous root formation" and discusses "under next short-day condition" being needed for heavy tuber production.

Legnani, G., & Miller, W. B. (2001). Using photoperiod to manipulate flowering and tuberous root formation in seed Dahlias . Greenh. Prod. New, 11(13), 36-40.

The article consistently links "short days" (SD) to increased "tuberous root development" , "large, rounded, tuberous roots" , and "heavy tuberous roots enriched with carbohydrates".

The study's "Summary" and "Experiment 3" directly connect "short day treatment" to "increased the diameters of roots" and "tuberous root formation". The observation that adventitious roots "developed in the tuberous roots... especially after October" points to seasonal cues that include cooling.

While the article directly studies the impact of high temperatures (heat stress) on dahlia buds and flowers, its findings implicitly support that optimal (cooler) temperatures are beneficial by demonstrating the severe negative effects of excessive heat. It defines "upper base temperature (TB)" for dahlia during the reproductive phase, with values provided as 33.1°C. The study's conclusion states that "Irreversible heat injury in buds and flowers of open field grown dahlia start when air temperature reaches 35°C". While not directly stating "cool temperatures trigger tuber formation," the identification of lethal high temperatures for flower parts (which are connected to the plant's overall reproductive effort and energy allocation) implies that temperatures below this damaging threshold, characteristic of cooler conditions, would be beneficial for overall plant health and development.

Claim 6.2: Excess artificial light or high nitrogen fertilizer early on can delay or suppress tuber formation.

Zimmerman, P. W., & Hitchcock, A. E. (1929). Root formation and flowering of dahlia cuttings when subjected to different day lengths . Botanical Gazette, 87(1), 1-13.

The article states that "Nitrates accumulated in the leaves and stems of short day plants, but were absent or present in only small amounts in long day plants". It further explains that "carbohydrates accumulate in the short day plants, presumably because there is relatively little utilization of them in the synthesis of nitrates to other forms of nitrogen" and that when "vegetative growth is checked" (as by short days), carbohydrates and nitrates accumulate, leading to "the plants take on the appearance of approaching dormancy". This supports the idea that conditions which suppress vegetative growth (like short days, or implicitly, too much of a growth-promoting nutrient like nitrogen early on) can lead to the accumulation of key resources, particularly carbohydrates and nitrates, that are essential for tuber formation.

TUCHIYA, S. (1993). Studies on the Production of Tuberous Roots in Dahlia . Special bulletin of Ishikawa Agricultural College, 18, 70-73.

Chapter 4 investigates "Influence of Nutrients on Formation of Tuberous Roots". It notes that "under short-day conditions, nutrient absorption dropped off radically, but absorbed nutrients were transferred to tubers with their thickening". It emphasizes "The fertilizer application until late-September is important for the production of tuberous roots in dahlia", implying a specific timing for nutrient importance that avoids "excess" earlier.

Chaudhary, S., Roy, S., Mishra, S. K., Tiwari, P., & Pandey, J. (2020). Effect of integrated nutrient management on flowering and flower yield of dahlia (Dahlia variabillis L.) Cv. Kenya orange . Journal of Pharmacognosy and Phytochemistry, 9(6), 2281-2283.

The study investigates integrated nutrient management (INM) strategies involving organic manures and biofertilizers with a recommended dose of fertilizer (RDF). The results indicate that various INM combinations significantly influence flowering parameters, including delaying the days to first flowering and 50% flowering compared to control, and affecting flower size and length. This demonstrates that nutrient applications (like nitrogen components within RDF) can affect plant development timing.

Claim 6.3: Integrated nutrient management, combining inorganic fertilizers with organic manures and bio-inoculants, significantly improves plant growth and tuber yield in dahlias.

Raghunandan, T., Collis, J. P., Saravanan, S., & Barman, K. S. (2021). Effect of Integrated Nutrient Management on Plant Growth and Tuber Yield of Dahlia (Dahlia variabilis) cv. Kenya White . International Journal of Plant & Soil Science, 33(24), 80-84.

The study directly investigates integrated nutrient management. Its findings show that a specific treatment combining 75% Recommended Dose of Fertilizer, Azotobacter, Farm Yard Manure, and Vermicompost significantly achieved maximum vegetative and Tuber yield attributes, including plant height, plant spread, number of branches, and number of leaves. This treatment also significantly maximized tuber yield attributes, such as the number of tubers per plant, maximum tuber weight, and maximum tuber yield per plant. The study's conclusion confirms that this integrated approach of applying recommended fertilizers with organic manures and biofertilizers "showed significant improvement in all growth and yield parameters of Dahlia", thus directly supporting that integrated use of these components significantly improves both plant growth and tuber yield.

Pandey, S. K., Kumari, S., Singh, D., Singh, V. K., & Prasad, V. M. (2017). Effect of biofertilizers and organic manures on plant growth, flowering and tuber production of dahlia (Dahlia variabilis L.) Cv. SP Kamala . International Journal of Pure & Applied Bioscience, 5(2), 549-555.

This study found that a specific combination of vermicompost and beneficial bacteria (Azotobacter and Phosphorous Solubilizing Bacteria) significantly increased various measures of plant growth (such as height, branching, and leaf count), flower production (including flower number and yield), and overall tuber yield (both tuber weight and count). The conclusions of the study explicitly confirm that this integrated treatment was superior for plant growth, flower yield, and tuber yield. This clearly demonstrates that combining organic manures and biofertilizers significantly improves both dahlia plant growth and tuber yield.

El-Alsayed, Sohier G., Sahar Ismail, and Doaa Eissa. Impact of seaweed extract and phosphorus application on productivity of dahlia plants . Assiut Journal of Agricultural Sciences 49, no. 1 (2018): 159-188.

The study investigates the impact of seaweed extract (an organic/bio-stimulant) and phosphorus (inorganic fertilizer) on dahlia plants. Its findings demonstrate that applying seaweed extract at 1% and phosphorus at 200 ppm significantly enhanced various vegetative growth parameters, including stem length, stem dry weight, number of leaves, and leaf area. Crucially, these treatments also significantly increased both the fresh weight and the number of tuberous roots per plant. The study's conclusion confirms that the application of phosphorus and seaweed extract, individually and in combination, "positively enhanced plant growth, development, yield and the mineral composition of Dahlia plants". This demonstrates that combining inorganic phosphorus with seaweed extract significantly improves both plant growth and tuber yield.

Swedan, E. A., Ahmed, M. A., Jiménez-Ballesta, R., & El-Kinany, R. G. (2023). Biological substances as stimulants-inducing growth, flowering, and chemical constituents in Dahlia plants . Cogent Food & Agriculture, 9(2), 2282237.

The study directly investigates the impact of various bio-stimulant treatments (salicylic acid, ascorbic acid, and Moringa oleifera leaf extract, and their combinations) on Dahlia pinnata. The article explicitly states that "the application of various bio-stimulant treatments, either individually or in combination, resulted in enhanced vegetative growth character-istics, flowering attributes, and tuberous root production". The "Conclusions" section reiterates that these treatments "exhibited a positive impact on the growth, flowering, yield, and mineral composition of dahlia plants". Table 9 presents detailed results for "Number of tuberous roots/plant" and "Fresh weight of tuberous roots/plant (g)," showing significant increases with various treatments compared to the control.

TUCHIYA, S. (1993). Studies on the Production of Tuberous Roots in Dahlia . Special bulletin of Ishikawa Agricultural College, 18, 70-73.

Chapter 4 directly investigates "the influence of nutrients on the formation and thickening of tuberous roots", outlining absorption and accumulation processes over growing stages, and concluding that timed fertilizer application is important for tuberous root production.

Sheergojri, G. A., Rather, Z. A., Khan, F. U., Nazki, I. T., & Qadri, Z. A. (2013). Effect of chemical fertilizers and bio-inoculants on growth and flowering of dahlia (Dahlia variabilies Desf.) cv.‘Pink Attraction’ . Applied Biological Research, 15(2), 121-129.

This article directly studies the effect of chemical fertilizers and bio-inoculants on dahlia's vegetative and floral characteristics. It provides extensive evidence that these practices significantly improve various plant growth parameters (e.g., plant height, number of branches, leaf area) and flower yield/quality (e.g., flower diameter, number of flowers, fresh flower weight, vase life). While it mentions effects on the timing of tuber emergence and sprouting, the results presented in the paper do not explicitly report significant improvement in overall tuber yield (quantity or weight). Therefore, the article supports the "plant growth" part of this claim but not the "tuber yield" part as written.

Claim 6.4: Phosphorus is fundamental for root development and energy transfer, foundational for tuber formation, while Potassium is vital for carbohydrate transport and storage, directly impacting tuber bulking.

The article explains phosphorus's vital role as an essential element for metabolic processes such as respiration and photosynthesis, which are fundamental for energy transfer in the plant. It specifically notes P's role in stimulating tuberous root formation, enabling greater absorption of elements crucial for development. Furthermore, the study links phosphorus to the activation of enzymes for carbohydrate transformation and the regulation of sugar consumption, emphasizing its role in "translocation of produced sugar and accumulation in the plant organs" (including tubers), directly impacting tuber bulking.

TUCHIYA, S. (1993). Studies on the Production of Tuberous Roots in Dahlia . Special bulletin of Ishikawa Agricultural College, 18, 70-73.

Chapter 4 states that "nutrient elements kept in the top were transferred to the tuberous toots" and discusses the vigorous thickening of tuberous roots with growth of nutrient elements contained in them.

The article, while focusing on water management, does discuss the impact on "total and reducing sugar content" in plants. It states that "The observed rise in carbohydrate content could potentially be attributed to the activation of the photosynthetic machinery... a result of the stimulatory effect exerted by the biostimulants used on the photosynthetic process". And in the discussion, "the total and reducing sugar content was higher in the leaves of dahlias subjected to controlled watering". This directly relates to carbohydrate content and implies their importance in plant physiological processes.

Claim 6.5: Allowing plants to grow for a week or two after blooming slows, as long as frost hasn't killed foliage, can promote continued tuber swelling and eye formation.

General horticultural practice, supported by understanding of continuous photosynthesis and resource translocation to storage organs.

TUCHIYA, S. (1993). Studies on the Production of Tuberous Roots in Dahlia . Special bulletin of Ishikawa Agricultural College, 18, 70-73.

Chapter 2, point 4 states that "Some of [the] tuberous roots in mid-September grew to the same size as the tuberous roots in early December. However, the weight, the rate of dry matter and carbohydrates of the tuberous roots were less in mid-September than in early December. They increased remarkably [from] mid-September to mid-November. It is clear that the optimum time of harvesting tuberous roots of dahlia is in mid-November". This directly supports that allowing plants to continue growth after mid-September (when blooming typically slows) promotes significant tuber swelling and accumulation of resources.

Online Resources

Dahlia Gall Disease: Unmasking Crown Gall and Leafy Gall is an article on this website by dahlia writer and educator Steve Lloyd. Learn how crown gall and leafy gall affect dahlias, and how to manage them. This in-depth, science-backed guide is for growers, breeders, and curious gardeners.

Don’t Fear Nitrogen: Feed Your Dahlias Right from the Start is an article on this website by dahlia writer and educator Steve Lloyd. It discussed the importance of nitrogen for dahlias early in the season, the critical period of growth that helps determine each plant’s tuber-making capacity.

A Gardener’s Primer to Mycorrhizae: Understanding How They Work and Learning How To Protect Them is an article hosted by Washington State University and written by Linda Chalker-Scott , a horticultural professor and author.

Gardening Myths BUSTED is a 3-part program on the Joe Gardener podcast series, with guest Linda Chalker-Scott. Listen to Part 1 or read the transcript of Chalker-Scott’s conversation with gardening author, TV host and educator Joe Gardener. There are links to parts 2 and 3 of the program.

How to Propagate Dahlia Cuttings is an article on this website by dahlia writer and educator Steve Lloyd. It explains the process he uses to root dahlia cuttings, and covers their cultivation and indoor lighting needs during their critical early weeks of growth.

Learn the Basics of Lifting Your Dahlia Tubers is an article on this website by dahlia writer and educator Steve Lloyd. Digging up a dahlia clump may seem easy, but understanding the proper techniques to avoid damaging them is the first step in preserving the all-important propagation resource detailed in the “Dahlia Tubers, Demystified” article series.

Mastering Dahlia Tuber Storage: A Practical Guide Rooted in Science is an article on this website by dahlia writer and educator Steve Lloyd. For growers who lift and store their dahlia tubers through the winter months, learning the optimal digging time and proper storage practices will help ensure viability the following season.

The Physiology of Adventitious Roots , an article hosted by the U.S. National Institutes of Health's National Library of Medicine. The illustrations are particularly helpful.

PropG is a web glossary application designed by the authors of the world standard textbook: Hartmann and Kester's Plant Propagation: Principles and Practices . Over 500 terms, images and videos are provided under nine major subject areas. These include Biology of Propagation, Propagation Environment, Genetic Selection, Seed Propagation, Cutting Propagation, Budding and Grafting, Bulbs and Other Geophytes, Layering and Division, Tissue Culture and Micropropagation.

Quince Flowers with guest Dr. Keith Hammett . Dr. Hammett is a horticulture scientist and renowned dahlia breeder from New Zealand. While a guest on the Quince Flowers podcast, he discussed how a cultivar’s tuber-making characteristics can help guide its fate in the market for dahlias.

Simply Soil Testing USA of Burlington, Washington provides comprehensive soil testing for customers throughout the United States with a convenient mail-in option. Test results are delivered electronically and come include a list of recommended amendments, with organic options.

A Soil Chemistry Primer: How Protons and Electrons Influence Soil Moisture and Fertility with guest retired horticulture professor Debbie Flower in conversation with gardening author, TV host and educator Joe Gardener.

What Is a Geophyte? an article on the Coastal Gardener website of the University of California Department of Agriculture and Natural Resources.

Full Bibliography

This bibliography includes all peer-reviewed articles and authoritative texts that directly support the claims and conclusions presented in the Dahlia Tubers Demystified series (Parts 1–6). The list is organized alphabetically for ease of reference.

Most sources were reviewed in full. When only the abstract was available, the citation is marked with “Abstract only accessed.” Direct links are provided for all sources. Where a publication is behind a paywall, I have noted “Academic Paywall” for readers who may have access through a library or institution.

For readers interested in the specific research behind our discussions, this list provides complete citation details for locating the sources. The author has verified that every hyperlink actively points to the corresponding article as of August 2025.

Ali, E. O. H. (2004). Pathological studies on dahlia tuber rots (Doctoral dissertation, Department of Agricultural Botany, Faculty of Agriculture at Moshtohor, Zagazig University).

Aoba, T., Watanabe, S., & Saito, C. (1960). Studies on tuberous root formation in dahlia. I Periods of tuberous root formation in dahlia . Journal of the Japanese Society for Horticultural Science, 29(3), 247-252. [Author’s note: Written in Japanese. English translation provided by Gemini AI and verified by ChatGPT 4o.]

Aoba, T., Watanabe, S., & Soma, K. (1961). Studies on the formation of tuberous root in dahlia. II Anatomical observation of primary root and tuberous root . Journal of the Japanese Society for Horticultural Science, 30(1), 82-88.

Biran, I., Gur, I., & Halevy, A. (1972). The relationship between exogenous growth inhibitors and endogenous levels of ethylene, and tuberization of dahlias. Physiologia Plantarum, 27(2), 226-230. Abstract Only Accessed. Academic Paywall.

Biran, I., & Halevy, A. H. (1973). The relationship between rooting of Dahlia cuttings and the presence and type of bud . Physiologia Plantarum, 28(2), 244-247. Abstract Only Accessed. Academic Paywall.

Biran, I., Leshem, B., Gur, I., & Halevy, A. H. (1974). Further studies on the relationship between growth regulators and tuberization of dahlias . Physiologia Plantarum, 31(1), 23-28. Abstract Only Accessed. Academic Paywall.

Brøndum, J. J., & Heins, R. D. (1993). Modeling temperature and photoperiod effects on growth and development of dahlia . JOURNAL-AMERICAN SOCIETY FOR HORTICULTURAL SCIENCE, 118, 36-36.

Chaudhary, S., Roy, S., Mishra, S. K., Tiwari, P., & Pandey, J. (2020). Effect of integrated nutrient management on flowering and flower yield of dahlia (Dahlia variabillis L.) Cv. Kenya orange . Journal of Pharmacognosy and Phytochemistry, 9(6), 2281-2283.

El-Alsayed, Sohier G., Sahar Ismail, and Doaa Eissa. Impact of seaweed extract and phosphorus application on productivity of dahlia plants . Assiut Journal of Agricultural Sciences 49, no. 1 (2018): 159-188.

Elsadek, A. (2018). Improvement yield and quality of dahlia flowers by exogenous application of gibberellic acid and salicylic acid under sandy soil conditions . Journal of Plant Production, 9(3), 289-297.

Fatima, B., Usman, M., Ashraf, T., Waseem, R., & Ali, M. A. (2007). In vitro shoot regeneration from cotyledon and hypocotyl explants of dahlia cultivars . Pak. J. Agri. Sci, 44(2), 312-316.

Halevy, A. H., & Biran, I. (1974, April). Hormonal regulation of tuberization in Dahlia . In II International Symposium on Flower Bulbs 47 (pp. 319-330). Abstract Only Accessed. Academic Paywall.

Hegde, B. N., Shirol, A. M., Harshavardhan, M., & Kumar, P. P. Genetic Divergence Analysis of Dahlia (Dahlia variabilis L.) Genotypes .

Hetman, J., Łukawska-Sudoł, S., Pudelska, K., & Parzymies, M. (2017). The effect of the cutting method on rooting of Dahlia pinnata Cav. cuttings . Acta Scientiarum Polonorum Hortorum Cultus, 16(2), 149-160.

Ivanova, V., & Zaprjanova, N. (2020). Study on phenological behaviours of Dahlia variabilis Hort. in overwintering of tuberous roots in the soil .

Khan, F. U., & Tewari, G. N. (2003). Effect of growth regulators on growth and flowering of dahlia (Dahlia variabilis L.) . Indian Journal of Horticulture, 60(2), 192-194.

Konishi, K., & Inaba, K. (1964). Studies on flowering control of dahlia. I. On optimum day-length . Journal of the Japanese Society for Horticultural Science, 33(2), 171-180.

Konishi, K., & Inaba, K. (1967). Studies on flowering control of dahlia. VII On dormancy of crown-tuber. Journal of the Japanese Society for Horticultural Science, 36(1), 131-140.

Kumar, T., Rinu, R. S., & Praddyum, S. T. A comprehensive review of Plant Growth Regulators (PGRs) and their impact on flowering and ornamental crops with insights into effective application methods.

Legnani, G., & Miller, W. B. (2000). Night Interruption Lighting Is Beneficial in the Production of Plugs of Dahlia Sunny Rose' . HortScience, 35(7), 1244-1246.

Legnani, G., & Miller, W. B. (2001). Using photoperiod to manipulate flowering and tuberous root formation in seed Dahlias . Greenh. Prod. New, 11(13), 36-40.

Menzel, C. M. (1985). The control of storage organ formation in potato and other species: a review. Part 1 . Abstract Only Accessed. Academic Paywall.

Menzel, C. M. (1985). The control of storage organ formation in potato and other species: a review. Part 2 .

Mills-Ibibofori, T., Dunn, B. L., Maness, N., & Payton, M. (2019). Effect of LED lighting and gibberellic acid supplementation on potted ornamentals . Horticulturae, 5(3), 51.

Pal, S. L. (2019). Role of plant growth regulators in floriculture: An overview . J. Pharmacogn. Phytochem, 8, 789-796.

Phetpradap, S., Hampton, J. G., & Hill, M. J. (1994). Effect of hand pinching and plant growth regulators on seed production of field grown hybrid dahlia . New Zealand journal of crop and horticultural science, 22(3), 313-320.

Pudelska, K., Hetman, J., Łukawska-Sudoł, S., & Parzymies, M. (2015). The efficiency of mother crowns and quality of soft cuttings of a few dahlia cultivars . Acta Scientiarum Polonorum Hortorum Cultus, 14(6), 189-200.

Raghunandan, T., Collis, J. P., Saravanan, S., & Barman, K. S. (2021). Effect of Integrated Nutrient Management on Plant Growth and Tuber Yield of Dahlia (Dahlia variabilis) cv. Kenya White . International Journal of Plant & Soil Science, 33(24), 80-84.

Read, P. E., Dunham, C. W., & Fieldhouse, D. J. (1972). Increasing Tuberous Root Production in Dahlia pinnata Cav. with SADH and Chlormequat1 . HortScience, 7(1), 62-63.

Sao, B., & Verma, L. S. (2021). Effect of rooting hormones in propagation of dahlia (Dahlia variabilis L.) through stem cutting . Journal of Pharmacognosy and Phytochemistry, 10(2), 887-891.

Schneck, K. K., Boyer, C. R., & Miller, C. T. (2021). Supraoptimal Root-zone Temperatures Affect Dahlia Growth and Development . HortTechnology, 31(6), 667-678.

TUCHIYA, S. (1993). Studies on the Production of Tuberous Roots in Dahlia . Special bulletin of Ishikawa Agricultural College, 18, 70-73.

Zimmerman, P. W., & Hitchcock, A. E. (1929). Root formation and flowering of dahlia cuttings when subjected to different day lengths . Botanical Gazette, 87(1), 1-13.

AI Collaboration Transparency

This article was created through a collaborative process between the author—a dahlia grower and educator—and an AI language model trained on scientific and botanical texts. The author guided the structure, tone, and emphasis of the article, and provided the scientific sources that form its foundation.

The author carefully reviewed every article at each stage to ensure factual accuracy, clarity, and accessibility.

The AI was used as a research and writing assistant, helping to summarize technical material, suggest phrasing, and—as part of a guided review process—link every substantive scientific statement, conclusion, and principle to one or more published, peer-reviewed source articles.

All content was shaped, reviewed, and refined by the author to ensure clarity and usefulness for readers interested in the science of dahlias.

A close-up of dahlia tubers infected with Leafy Gall

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Science of Sanitation: Protect Dahlias from Deadly Pathogens

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Part 7: For Curious Readers & Researchers

Table of Contents

Recap: What the Series Covered

Glossary

Scientific Claims and Supporting Documentation

From Part 1: What Makes a Tuber a Tuber?

Claim 1.1: Dahlia tubers are storage organs that allow the plant to survive adverse conditions and regrow.

Claim 1.2: Unlike true bulbs or corms, dahlia tubers are swollen adventitious roots, not modified stems.

Claim 1.3: Tuber formation in dahlias specifically involves the reprogramming of certain adventitious roots under specific environmental and hormonal cues.

From Part 2: What Makes a Dahlia Root Become a Tuber?

Claim 2.1: Tuber formation in dahlias is largely influenced by photoperiod (daylength), typically favored by shorter days.

Claim 2.2: Cooler soil temperatures also contribute to robust tuber development.

Claim 2.3: Soil moisture and drainage are critical; waterlogging can inhibit tuber formation by reducing oxygen to the roots.

Claim 2.4: The critical window for tuber initiation typically occurs 4 to 8 weeks after planting, influenced by these environmental cues.

Claim 2.5: Hormonal balance, particularly the interaction between gibberellins (GAs) and abscisic acid (ABA), is key to tuberization. High GAs inhibit, while ABA promotes.

From Part 3: Why Some Dahlia Cuttings Don’t Make Tubers

Claim 3.1: High light intensity, particularly long daylength, and warmth during propagation of cuttings can suppress tuber formation.

Claim 3.2: Hormonal treatments, such as high levels of auxins used for rooting, can sometimes interfere with subsequent tuberization.

Claim 3.3: The physiological age of the cutting material (juvenility) can also influence its capacity for tuber formation.

Claim 3.4: Practices like taking cuttings too late in the season, when mother plants are already signaling tuberization, can improve tuber yield from cuttings.

From Part 4: Disrupted Tuber Formation: What’s Really Going On?

Claim 4.1: Commercial growth regulators (CGRs) are used to manipulate plant architecture (e.g., height, branching) and flowering time for market purposes, which can have downstream effects on tuber formation.

Claim 4.2: Specific CGRs like Ethephon, Daminozide (Alar), SADH, and Maleic Hydrazide (MH) impact plant growth by altering hormonal balances, potentially affecting resource allocation for tuber development.

Claim 4.3: Dahlias purchased as potted plants from garden centers may have been treated with CGRs, which can alter their initial growth habit and potentially delay or reduce tuberization compared to tubers grown for propagation.

From Part 5: Are Tuber Traits Genetic?

Claim 5.1: Tuber formation in dahlias is a polygenic trait, meaning it is influenced by multiple interacting genes rather than a single gene.

Claim 5.2: Different dahlia cultivars exhibit varying tendencies for tuber size, shape, eye formation, and storability, even under ideal conditions, due to genetic differences.

Claim 5.3: Breeders can select for tuber-forming traits through seedling selection over generations.

From Part 6: The Science of Better Tuber Harvests

Claim 6.1: Cool, moist soil and shortening daylength are key triggers for robust tuber formation.

Claim 6.2: Excess artificial light or high nitrogen fertilizer early on can delay or suppress tuber formation.

Claim 6.3: Integrated nutrient management, combining inorganic fertilizers with organic manures and bio-inoculants, significantly improves plant growth and tuber yield in dahlias.

Claim 6.4: Phosphorus is fundamental for root development and energy transfer, foundational for tuber formation, while Potassium is vital for carbohydrate transport and storage, directly impacting tuber bulking.

Claim 6.5: Allowing plants to grow for a week or two after blooming slows, as long as frost hasn't killed foliage, can promote continued tuber swelling and eye formation.

Online Resources

Full Bibliography

Further Reading

AI Collaboration Transparency