Dahlia Doctor Research Library: Dahlia Planting Dates and Crop Scheduling

A Curated Knowledge Card Collection

Copyright © 2026 by Steve K. Lloyd
All Rights Reserved

Dahlia growers have always known that timing shapes outcomes. Plant too late and tubers run short. Sow too early and cold temperatures stall germination. Delay the forcing schedule and a cut-flower crop can miss its intended market window. But for most of dahlia's commercial and garden history, these lessons were passed down as lore rather than tested as science.

The research collected here treats timing as an independent variable: something to manipulate, measure, and optimize. The studies span seed sowing, vegetative propagation, field planting dates, greenhouse forcing, pot-root production, and multi-environment field trials. They draw from Japan, India, Pakistan, Romania, Bulgaria, Mexico, and the United States, representing a range of climates, production systems, and crop goals. What unifies them is a shared question: when you change the calendar, what changes in the plant?

The answers are not simple. Timing interacts with cultivar, climate, photoperiod, growing environment, and crop purpose in ways that resist universal prescription. But taken together, the studies in this collection offer something more useful than rules: they offer a framework for thinking about scheduling as a biological and agronomic tool, grounded in how dahlias actually develop.

Each post in this series presents a curated set of Dahlia Doctor Knowledge Cards organized around a specific research topic. A Knowledge Card summarizes one scientific or technical source using a consistent structure: study system, experimental context, experimental design, key results, mechanistic insight, practical guidance, and why the source matters to dahlia growers and researchers. These summaries represent original interpretive work. They are intended as a research guide, not a substitute for reading the original papers. Each citation title links to a Google Scholar search for that source, opening in a new tab, except where a direct source link is more appropriate.

Each Knowledge Card appears once in this collection, placed in the topic cluster where it contributes most directly. Some sources are relevant to more than one cluster; placement reflects primary emphasis rather than exclusive relevance.

Two KCs in the Field Planting Dates and Seasonal Establishment section share notable connections. KC-0035 and KC-0037 share the same first author (M. Kumar), the same publication year (2024), the same cultivar set (Anarkali, Gargi, Giani Zail Singh, Matungini, and Suryadev), and the same study location in Himachal Pradesh, India. KC-0037 is a doctoral dissertation; KC-0035 is a journal article drawn from or closely related to that dissertation's field production experiment. Their results are consistent, and their practical conclusions align. They are treated here as related but not duplicate sources, since the dissertation covers a broader scope including propagation trials and economic analysis not present in the journal article.

KC-0035 carries an internal date discrepancy. The abstract and methods sections of the source describe planting dates of September 15, October 15, and November 15, while the results tables report October 15, November 15, and December 15. The KC and its Practical Guidance reflect the dates associated with the reported results rather than the abstract dates. Readers consulting the original source should be aware of this inconsistency.

KC-0004 appears in the Seasonal Boundaries for Tuber and Pot-Root Production section in a narrowly defined role. It was included in the Dahlia Doctor Research Library: Tuberous Root Formation and Development collection. Its appearance here is limited to what it contributes specifically to understanding the seasonal timing of tuberous-root formation: the crop-calendar question of when in the growing season adventitious roots begin forming and when enlargement accelerates. Readers interested in the full developmental biology of tuberous roots are directed to that earlier collection.

KC-0335 is a brief one-page bulletin source. It is included because its June, July, and August cutting-time comparison fits this collection's crop-scheduling theme, especially for cool, short-season production. It should be read as a small but useful production note rather than as a comprehensive experimental treatment of pot-root physiology.

Publication Type
Experimental Research Article

Full Citation
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.

Study System
Dahlia variabilis L.; five cultivars: Anarkali, Gargi, Giani Zail Singh, Matungini, and Suryadev; rooted cuttings grown for tuber production under low hill field conditions in Himachal Pradesh, India.

Experimental Context
Field evaluation under low hill conditions in Himachal Pradesh, India. Three planting-date treatments were applied across five cultivars in a factorial design, with tuber production traits as primary outcome variables.

Experimental Design
Factorial randomized block design with five cultivars and three planting-date treatments, three replications, 15 treatment combinations, 45 experimental plots, and nine plants per plot at 45 cm × 45 cm spacing. Recorded traits included plant height, plant spread, internodal length, number of tubers per plant, tuber diameter, tuber length, tuber weight per plant, and tuber yield per plot.

Key Results
Among cultivars, Suryadev recorded the greatest mean plant height and internodal length. Matungini recorded the greatest mean plant spread, number of tubers per plant, and tuber length. Giani Zail Singh recorded the greatest mean tuber diameter. Anarkali recorded the greatest mean tuber weight per plant and tuber yield per plot. For planting dates, the results tables report October 15 as producing the highest mean number of tubers per plant, tuber diameter, tuber length, tuber weight per plant, and tuber yield per plot, outperforming November 15 and December 15.

Note: The abstract and methods sections of this article describe planting dates of September 15, October 15, and November 15, while the results tables report October 15, November 15, and December 15. The results and conclusions presented here reflect the dates as reported in the results tables.

Mechanistic Insight
The article attributes cultivar differences in plant traits and tuber production to genetic traits, environmental conditions, soil composition, and cultivar response to environmental circumstances, and states that these factors may influence tuber development and weight.

Practical Guidance
Under the reported low hill conditions of Himachal Pradesh, the October 15 planting date was associated with the best tuber production outcomes across measured traits. Cultivar selection also matters: Anarkali for tuber weight and yield per plot, Matungini for tuber number and length, and Giani Zail Singh for tuber diameter.

Why This Source Matters
This is the anchor planting-date study in this collection. It provides direct field trial evidence that the timing of planting affects tuber production outcomes in dahlia, and that cultivar and planting date interact in ways that affect which traits are maximized.

Publication Type
Thesis/Dissertation

Full Citation
Kumar, M. (2024). Studies on propagation and production technology in dahlia (Dahlia variabilis L.) (Doctoral dissertation, Dr. Yashwant Singh Parmar University of Horticulture and Forestry).

Study System
Dahlia variabilis L.; five cultivars: Anarkali, Gargi, Giani Zail Singh, Matungini, and Suryadev; terminal cuttings and field-grown rooted plants under low hill conditions in Himachal Pradesh, India.

Experimental Context
A doctoral dissertation covering two distinct experiments: a propagation trial evaluating cutting performance under protected mist-chamber conditions, and a field production trial evaluating growth, flowering, vase life, tuber traits, and economic return across planting dates and cultivars.

Experimental Design
The propagation experiment used a factorial completely randomized design with five cultivars, three propagation times, three rooting media (sand; cocopeat plus sand; cocopeat plus sand plus farmyard manure), three replications, and 30 cuttings per replication. The field production experiment used a factorial randomized block design with five cultivars, three planting dates, three replications, nine plants per plot, and 45 cm × 45 cm spacing.

Key Results
In the propagation experiment, September 15 produced the highest quality rooted cuttings. Cocopeat plus sand produced the best overall rooting-media performance. In the field production experiment, October 15 produced the highest number of cut stems per plant, flower yield per plot, number of tubers per plant, tuber yield per plot, tuber diameter, tuber length, tuber weight per plant, and tuber weight per plot. November 15 produced the highest vase life. Among cultivars, Matungini recorded the highest flower yield per plot, number of tubers per plant, tuber length, and benefit-cost ratio. Anarkali recorded the highest tuber yield and tuber weight. Giani Zail Singh recorded the highest tuber diameter. Suryadev recorded the highest plant height, stem girth, flower stem length, cut stem weight, and vase life.

Mechanistic Insight
The dissertation relates propagation performance to propagation time, rooting-media composition, and cultivar differences. It relates production differences to planting date, cultivar response, and growing conditions affecting vegetative growth, flowering, vase life, tuber development, and yield traits.

Practical Guidance
For quality rooted cutting production under the tested low hill conditions, September 15 and cocopeat plus sand medium are identified. For flower and tuber production, October 15 is identified. For vase life, November 15 is identified. These findings are consistent with the companion journal article KC-0035, and both should be read together as complementary treatments of the same cultivar set and field context.

Why This Source Matters
As a doctoral dissertation, this source integrates propagation timing, rooting media, planting date, and cultivar performance into a single study framework covering the full production arc from cutting to harvest. It connects propagation scheduling with field production scheduling in a way that the companion journal article alone does not.

Publication Type
Experimental Research Article

Full Citation
Ivanova, V., & Zaprjanova, N. (2020). Study on phenological behaviours of Dahlia variabilis Hort. in overwintering of tuberous roots in the soil. Scientific Papers. Series B, Horticulture, 64(1), 588–591.

Study System
Dahlia variabilis Hort.; cultivars Vitus, White Ball, and Dark Red; tuberous roots overwintered in soil compared with tuberous roots lifted, stored, and replanted the following spring.

Experimental Context
Field study under conditions where standard local practice involved spring planting, autumn lifting, and winter storage above 0°C in a dark ventilated place. The experiment compared that standard practice against leaving tuberous roots in the soil over winter with stems cut to 10 cm in October.

Experimental Design
Tuberous roots of similar length and diameter were selected, each with part of the old stem. Plants were established in the second half of April. Control plants were lifted in the second half of October, cleaned, stored through winter, and replanted the following April. Experimental plants had stems cut to 10 cm in October and tuberous roots left in the soil for the next growing season. Vegetative and ornamental phenological traits were measured during the second vegetation period.

Key Results
Overwintered plants began sprouting earlier by 15 to 27 days, depending on cultivar, and reached mass emergence 21 to 43 days earlier than lifted-and-replanted plants. Overwintered plants reached maximum growth earlier, generally at the beginning of June, while lifted-and-replanted plants reached maximum growth later in the season. Beginning of flowering occurred earlier in overwintered plants by 5.2 to 13.1 days after emergence, and mass flowering occurred earlier by 8.17 to 14.4 days. Individual flowers lasted 1.7 to 5.4 days longer on overwintered plants. Whole-plant flowering duration was longer in overwintered plants by 37.9% to 45%.

Mechanistic Insight
The study states that budding duration was not affected by cultivation mode, attributing this to the fact that dahlia behaves as a short-day-responsive plant for some developmental processes. Cultivar and overwintering treatment were identified as the primary factors associated with differences in emergence timing, growth rate, and flowering duration.

Practical Guidance
Under the tested conditions, leaving tuberous roots in the soil over winter produced earlier emergence, faster early-season growth, earlier flowering, and longer flowering duration compared with lifting, storing, and replanting. The study notes that future work should monitor soil temperature, which may mediate some of these effects.

Why This Source Matters
This study gives the collection a distinctive grower-facing angle. The question of whether to lift or overwinter in soil is a practical one that every dahlia grower in a marginal climate considers, and this source provides phenological data showing that the decision has measurable downstream effects on the whole season's timing.

Publication Type
Experimental Research Article

Full Citation
Afzal, M., Ahmed, M. M., Shah, R. A., & Awan, B. M. (2000). Effect of different sowing times on the performance of dahlia (Dahlia variabilis). Pakistan Journal of Biological Sciences, 3(1), 150–152.

Study System
Seed-grown local Dahlia variabilis variety evaluated under field conditions in Rawalpindi, Pakistan.

Experimental Context
Seeds were sown at four fortnightly intervals beginning 10 September, seedlings raised in pots, and plants transplanted to field plots at 1.6-foot plant and row spacing.

Experimental Design
Randomized complete block design with four sowing-date treatments, four replications per treatment, and two seedlings per replication. Recorded traits were seed germination time, plant height, days to flower, blooming period, flower size, and seed yield per replication.

Key Results
The 25 September sowing produced the shortest germination time, tallest plants, longest blooming period, largest flowers, and highest seed yield per replication. The 25 October sowing flowered in the fewest days but had the shortest blooming period and lowest seed yield. All six measured traits differed highly significantly among sowing-date treatments.

Mechanistic Insight
The source associated rapid germination with an average sowing temperature of 25.9°C at the September 25 sowing date. It linked stronger plant growth, larger flower size, longer blooming period, and higher seed yield with the treatment that germinated fastest, and attributed the poor performance of October sowings to low post-germination temperatures that restricted vegetative growth before later temperature rise allowed flowering.

Practical Guidance
For the tested Rawalpindi conditions, 25 September was identified as the best sowing time. The source states that dahlia flower availability can be preplanned by adjusting sowing time, a direct statement that sowing date is a scheduling tool, not merely a cultural decision.

Why This Source Matters
This is a clean, well-structured sowing-time trial covering six traits simultaneously. It demonstrates that germination temperature, post-germination growth conditions, and sowing date interact in predictable ways, and that optimizing the sowing window has compounding effects across the entire production season.

Publication Type
Journal Article

Full Citation
Pop, M. R. (2010). Determining the optimal sowing period at a variety from Dahlia variabilis species from Mignon group. Analele Universităţii din Oradea – Fascicula Biologie, XVII(1), 180–182.

Study System
Dahlia variabilis, Mignon Group; greenhouse pot production; sowing dates compared for early and extended flowering performance.

Experimental Context
Randomized block experiment with four autumn sowing dates conducted in a greenhouse pot production context, evaluating sowing time for its effects on flowering timing, duration, plant size, flower size, and seed yield.

Experimental Design
Four sowing-date treatments, multiple replications per treatment, measured across a range of vegetative and ornamental traits including plant height, average flower surface, blooming period, and seed yield.

Key Results
Late September sowing maximized flowering duration, flower size, plant height, and seed yield under the study conditions. Earlier and later sowings were associated with reduced performance across these traits.

Mechanistic Insight
Earlier vegetative establishment under favorable greenhouse temperatures appears to improve developmental rate and downstream flowering performance. The relationship between sowing date, germination conditions, and subsequent phenological outcomes mirrors the pattern observed in KC-0001, though here under protected rather than field conditions.

Practical Guidance
In this greenhouse study, late September sowing performed best for the tested Mignon-type dahlia. Direct scheduling decisions should be adjusted for cultivar, climate, production goal, and production environment, since results in protected culture may not transfer directly to open-field systems.

Why This Source Matters
This study extends the sowing-date literature specifically to Mignon-group dahlias under greenhouse conditions, a combination not addressed by most field-based trials. Its consistency with KC-0001 across different production systems and geographies strengthens the broader case that sowing timing is a reliable lever for managing flowering outcomes in seed-grown dahlias.

Publication Type
Experimental Research Article

Full Citation
Pop, M. R. (2010). Influence phenotypic performance achieved by sowing period in Dahlia variabilis. Journal of Horticulture, Forestry and Biotechnology, 14(1), 133–135.

Study System
Dahlia variabilis, Mignon group, Yellow Shades variety; seed-grown dwarf dahlia plants evaluated under different sowing periods for pot plant production for green space decoration.

Experimental Context
Monofactorial randomized block experiment with sowing period as the experimental factor. Four variants were tested: March 5 in a heated greenhouse, March 15 in a heated greenhouse, March 25 in a heated greenhouse, and April 15 in open field as the control variant.

Experimental Design
Four sowing-date variants with four replications each. Measured traits were plant height, average flower surface, and seed mass per plant.

Key Results
The March 25 greenhouse sowing recorded the highest values for plant height, average flower surface, and seed quantity per plant. The April 15 open-field control recorded the lowest values. Plant height for March 15 and March 25 greenhouse sowings was significantly higher than the control. Average flower surface was highest in the March 25 greenhouse variant and significantly greater than the control. Seed quantity per plant was positively correlated with flower surface.

Mechanistic Insight
The source attributes higher plant performance after March greenhouse sowing to consistently higher temperatures after germination and during the immediate early vegetation period. The positive correlation between flower surface and seed quantity indicates that sowing conditions that produce larger flowers also tend to produce greater seed yield.

Practical Guidance
For vigorous seed-grown Dahlia variabilis plants with larger flowers and more seeds in pot production, sowing during March 15–25 in heated greenhouses is recommended where conditions permit.

Why This Source Matters
This study adds a spring greenhouse sowing dimension that complements the autumn sowing evidence in KC-0226 and the field sowing evidence in KC-0001. Together, the three studies in this cluster bracket the range of sowing contexts for seed-grown dahlias: autumn field production, autumn greenhouse production, and spring protected production. All three point to temperature conditions during and immediately after germination as a primary driver of downstream performance.

Publication Type
Trade Publication Article

Full Citation
Lopez, R., & Brown, J. (2025, April 1). Secrets for early dahlia cut flower harvests. GrowerTalks.

Study System
Dahlia ×hybrida specialty cut flower cultivars Jan Ryecroft, Linda's Baby, Karma Prospero, and Salmon Runner grown from number 1 size tubers in a greenhouse at East Lansing, Michigan.

Experimental Context
Greenhouse study evaluating short-day photoinductive cycles after an initial long-day vegetative phase as a method for achieving earlier cut flower harvest dates.

Experimental Design
Tubers were planted in bulb crates in mid-March and grown at 72/64°F (22/17°C). LED fixtures extended natural daylength to 16-hour long days for seven weeks. Plants were pinched five weeks after transplant or when 15 to 18 inches tall. After seven weeks of vegetative growth, plants received continuous 16-hour long days, continuous nine-hour short days, or five, ten, fifteen, twenty, twenty-five, or thirty days of nine-hour short days applied with black cloth from 5:00 p.m. to 8:00 a.m.

Key Results
All plants eventually flowered under all daylength treatments. Time to harvest was reduced by increasing numbers of photoinductive short days compared with plants grown under continuous long days. Karma Prospero grown under 15 or 30 short days reached harvest 10 or 14 days earlier, respectively, than plants under continuous long days. Jan Ryecroft, Linda's Baby, and Salmon Runner reached harvest 8, 10, and 11 days earlier, respectively, after 30 short days compared with continuous long days. Stem length was generally greatest under continuous long days and five short days. Plants receiving 30 days or continuous short days produced the shortest stems. Total harvested stem number across cultivars was lowest under continuous short days, with plants in other treatments producing approximately 92% more stems.

Mechanistic Insight
Long daylengths promoted vegetative growth in dahlia, while short daylengths promoted flowering and tuber formation. Limited short-day cycles induced earlier flowering without the yield penalties associated with prolonged short-day exposure, which reduced stem length and, under continuous short days, reduced total stem production as plants shifted allocation toward tubers.

Practical Guidance
Dahlias should be grown under long days of at least 15 hours for at least five to seven weeks to promote vegetative development, then given ten to fifteen short days of nine to twelve hours using black cloth for flower induction. After induction, black cloth should be discontinued and plants returned to long days for the remaining production period to support stem length and flower quality. Field, greenhouse, or heated high tunnel growers can deliver this using black cloth over a simple PVC or metal structure placed without direct contact with plants.

Why This Source Matters
This article reframes photoperiod management as a crop-scheduling tool rather than a biological curiosity. Its practical protocol for using limited short-day cycles to shift harvest dates by ten to fourteen days provides directly actionable evidence for commercial cut flower producers seeking to program their crop calendar.

Publication Type
Peer-reviewed Journal Article

Full Citation
Durso, M., & De Hertogh, A. A. (1977). The influence of greenhouse environmental factors on forcing Dahlia variabilis Willd. Journal of the American Society for Horticultural Science, 102(3), 314–317.

Study System
Tuberous-rooted Dahlia variabilis cultivars Kolchelsee and Park Princess; greenhouse forcing of stored tuber clumps from January to June under controlled environmental conditions.

Experimental Context
Controlled greenhouse forcing study evaluating the effects of fertilization, temperature, light intensity, and photoperiod on flowering, plant quality, and development timing.

Experimental Design
Randomized complete block design with factorial evaluation of fertilizer, temperature, light intensity, and photoperiod treatments, with 15 plants per treatment.

Key Results
Fertilization was required for full flowering and improved plant quality. Optimal quality was achieved at 25°C day and 16°C night temperatures. High temperatures accelerated flowering but reduced plant quality. Fifty percent light reduction increased stem height and delayed flowering. An 8-hour photoperiod reduced flowering percentage and overall plant quality compared with longer photoperiods.

Mechanistic Insight
Temperature altered the rate of floral differentiation and the pace of vegetative growth. Reduced light promoted stem elongation without compensating improvements in flowering. Short photoperiod interfered with normal floral development and reduced the proportion of plants reaching full flower. Together, these findings indicate that temperature is the primary lever for managing crop speed in greenhouse forcing, while light and photoperiod primarily affect quality rather than timing alone.

Practical Guidance
For spring forcing, continuous fertilization, high light intensity, and approximately 25°C day and 16°C night temperatures are recommended. Short days and heavy shading should be avoided. Temperature can be adjusted to manage crop timing, with higher temperatures accelerating the schedule at the cost of some quality.

Why This Source Matters
This is one of a small number of controlled greenhouse forcing studies for dahlia published in a peer-reviewed journal. It provides the environmental parameters for managing forcing schedules and quantifies the tradeoffs between speed and quality under different temperature, light, and photoperiod regimes.

Publication Type
Peer-reviewed Journal Article

Full Citation
Barrett, J. E., & De Hertogh, A. A. (1978). Growth and development of forced tuberous-rooted dahlias. Journal of the American Society for Horticultural Science, 103(6), 772–775.

Study System
Dahlia × pinnata cultivars Park Princess and Miramar; greenhouse forcing from stored tuberous-root clumps under controlled conditions at Michigan State University.

Experimental Context
Four experiments examining dry-weight dynamics of tuberous roots, fibrous roots, and shoots over the forcing period; the effect of ancymidol on shoot growth; the tolerance of clump trimming on plant quality; and the relationship between early shoot height and days to flower.

Experimental Design
Experiment 1: 90 uniformly sized clumps of each cultivar planted April 9, 1976; destructive dry-weight harvests of 15 plants per cultivar at 0, 14, 21, 35, 49, and 63 days after planting. Experiment 2: 200 Park Princess clumps planted March 8, 1977; shoot dry weight and height compared with and without ancymidol at intervals. Experiment 3: 90 Park Princess clumps with varying degrees of fibrous root and tuberous root removal planted April 14, 1977; three five-plant replicates per six trimming treatments in a randomized complete block design. Experiment 4: 25 clumps per cultivar planted February 25–26, 1976, and 32 per cultivar planted February 17, 1977; plant height measured at 14 and 28 days and at flowering; linear correlation coefficients calculated between height, clump fresh weight, days to flower, and shoot dry weight.

Key Results
During the first 35 days after planting, tuberous-root dry weight declined to approximately 73% of initial weight while fibrous-root and shoot dry weights increased. From day 35 to day 63, total plant dry weight increased by 32 grams, with shoot growth accounting for 50% and new tuberous-root growth for 44%. New tuberous roots formed as adventitious roots at the basal nodes of the stem. Ancymidol reduced shoot dry weight and total plant height without altering tuberous-root or fibrous-root growth. Removing all fibrous roots before planting increased flower number and shoot dry weight compared with untrimmed controls. Removing half of each tuberous root was the only trimming treatment that reduced overall plant quality. Plant height at 14 and 28 days after planting was strongly and negatively correlated with days to flower, with correlation coefficients of −0.80 and −0.77 for Park Princess and Miramar, respectively. Clump fresh weight at planting was not correlated with days to flower or shoot dry weight.

Mechanistic Insight
During the first half of the forcing period, the plant operates in a reserve-mobilization phase: existing tuberous-root reserves are consumed to support early shoot and fibrous-root growth. During the second half, the plant shifts to net growth mode, building new shoot mass and initiating new tuberous roots adventitiously. Flower initiation does not occur until the shoot reaches a minimum size threshold. More vigorous early shooters reach that threshold sooner and flower earlier. This explains the negative correlation between early plant height and days to flower: early shoot growth rate, not clump size, predicts flowering time within a cultivar.

Practical Guidance
Selecting for uniform early shoot vigor at the time of planting, or segregating clumps by early height at 14 to 28 days, is the most direct way to reduce variation in flowering time within a forced batch. Clump trimming is tolerable as long as at least half the tuberous roots of each clump remain intact; fibrous-root removal does not penalize quality and may modestly improve it. Ancymidol at 0.75 mg per plant controls height without disrupting tuberous-root or fibrous-root dynamics.

Why This Source Matters
This paper provides the mechanistic foundation for understanding why forcing schedules vary within a cultivar and what can be done about it. The finding that early shoot height, not clump weight, predicts days to flower is directly actionable for growers managing crop uniformity in a forcing program.

Publication Type
Bulletin Article

Full Citation
Myodo, H., Okumura, J., & Chono, H. (1963). Study on pot-root production methods in dahlia. Bulletin of the Hokkaido Discussion Group of the Japanese Society of Breeding and the Japanese Society of Crop Science, 3.

Study System
Dahlia cultivated varieties; pot-root production for export-oriented bulb production under Hokkaido, Japan conditions.

Experimental Context
Brief bulletin report comparing soil media and cutting times for pot-root production in small plastic pots, evaluated under the short growing season and cool climate of Hokkaido.

Experimental Design
Factorial comparison of three soil media: cultured soil, river sand, and vermiculite, and three cutting times: early June, early July, and early August, for effects on pot-root number and weight.

Key Results
Cultured soil produced the highest pot-root number and weight among the media tested. June and July cuttings established successfully and produced pot-roots. August cuttings failed to form tubers under the tested conditions.

Mechanistic Insight
The failure of August cuttings to form tubers under Hokkaido conditions suggests that this production system had a seasonal boundary beyond which the remaining growing season was insufficient for usable pot-root formation. The success of June and July cuttings identifies a productive window for pot-root production in this cool-climate setting.

Practical Guidance
Under conditions similar to those reported in Hokkaido, early-summer cuttings in a productive soil medium appear more reliable for pot-root production than late-summer cuttings. The June-to-July window should be treated as the tested productive zone in this one-page bulletin source, while August cutting attempts were unsuccessful under the reported conditions.

Why This Source Matters
This brief source contributes a practical production-timing observation: in a cool, short-season region, pot-root production had a working calendar window. It is not a comprehensive study of dahlia tuber physiology, but it gives the collection a useful production example that pairs well with the more detailed seasonal physiology in KC-0004.

Publication Type
Experimental Research Article

Full Citation
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.

Study System
Dahlia seedlings from a single strain and plants of Tensin, a medium decorative white-flowered cultivar grown from tuberous roots; field-grown plants dug at approximately ten-day intervals from June to November.

Experimental Context
Field study examining the seasonal timing of adventitious root production and tuberous root enlargement under natural daylength, defoliation, shading, and photoperiod treatments. This KC appears here in a limited role: for its evidence on the seasonal calendar of tuberous-root initiation and enlargement. Readers interested in the full developmental biology of dahlia tuberous roots are directed to the Dahlia Doctor Research Library: Tuberous Root Formation and Development collection.

Experimental Design
Field plants dug at approximately ten-day intervals from June through November for sequential dry-weight and anatomical assessment. Defoliation treatments removed all expanded leaves at ten-day intervals. Shade treatments were applied during September to October or October to November. Short-day treatments applied an 8-hour photoperiod for 20 or 40 days. Long-day treatments used a continuous 24-hour photoperiod in August and September.

Key Results
Adventitious roots appeared successively from early June to early August. Root diameters increased from late June to November, with marked enlargement accelerating after October. Defoliation in June and July reduced adventitious root number. Defoliation after mid-September reduced root diameter more than root number. October shading reduced root diameter. Short-day treatment reduced adventitious root number while increasing root diameter. Long-day treatment showed no clear difference in root number or diameter compared with natural daylength.

Mechanistic Insight
Adventitious root initiation is concentrated in the early-to-mid growing season, from June through early August under the study conditions. Root enlargement then continues through autumn, with marked acceleration after October under natural daylength. This two-phase pattern, early initiation followed by late-season enlargement, means that the productive tuber crop depends on both early establishment of adventitious roots and preservation of the leaf canopy and favorable conditions into autumn.

Practical Guidance
A developmental period before short-day conditions is necessary to establish adequate adventitious root number. Early defoliation reduces root number; late defoliation or shading reduces root enlargement. For pot-root and tuber crop production, both phases of the seasonal tuber calendar, early root initiation and late-season enlargement, require protection from practices or conditions that interrupt them.

Why This Source Matters
In the context of this collection, this study provides the physiological timeline that helps explain why tuber and pot-root production have seasonal limits. Together, KC-0004 and KC-0335 suggest why pot-root production has a working calendar window: adventitious root initiation is concentrated earlier in the growing season, while later enlargement depends on an intact canopy and favorable autumn conditions.

Publication Type
Experimental Research Article

Full Citation
Villegas-Olguín, M. A., Mendoza-Villarreal, R., Benavides-Mendoza, A., García-Osuna, H. T., Cabrera-de la Fuente, M., & Robledo-Torres, V. (2023). Agronomic response of four Dahlia pinnata Cav. (Asteraceae) varieties in three production environments. Agrociencia, 57(8), 885–930.

Study System
Dahlia pinnata Cav. varieties Antje, Babylon, Boy Mick, and Canby Centennial grown from tuberous roots; evaluated under open field, semi-automated greenhouse, and 30 percent black shade net production environments in Saltillo, Coahuila, Mexico.

Experimental Context
Evaluation of growth, development, cut-flower quality, inflorescence production, and tuberous root production across three distinctly different production environments in a semi-arid Mexican highland setting.

Experimental Design
Tuberous roots of four varieties planted directly in soil beds under three production environments. Eight tuberous roots per variety per environment. Completely randomized design with four replicates and two experimental units per replicate, producing 12 variety-by-environment treatments. Variables included plant height, basal stem diameter, number of leaves, total inflorescences, days to flowering, number of tuberous roots, floral stem length, fresh inflorescence weight, inflorescence diameter, and floral stem diameter. Tukey mean comparisons and Pearson correlations calculated among selected variables.

Key Results
The shade net environment produced better results for six of eight evaluated variables. Antje under shade net had the greatest plant height and highest leaf number. Boy Mick under shade net had the greatest basal stem diameter and the highest total number of inflorescences. All four varieties under shade net produced the first inflorescence before 82 days. Babylon in open field produced the highest number of tuberous roots. Antje under shade net had the longest floral stems. Boy Mick in the greenhouse had the highest fresh flower weight. Canby Centennial in open field had the thickest floral stems. No significant differences were found for inflorescence diameter. Positive correlations were found among growth and production variables, with the strongest correlations between plant height and leaf number, and between plant height and total inflorescences.

Mechanistic Insight
Greater plant height under shade net was attributed to stem elongation in response to lower light levels. Lower leaf production in greenhouse plants was attributed to high temperature stress. Higher fresh flower weight in greenhouse-grown Boy Mick was associated with higher humidity promoting water absorption. The relationship between plant height, leaf production, and total inflorescences reflects the connection between vegetative development, node production, and the number of flowering stems the plant can support. Reduced radiation under shade net was associated with increased leaf area and leaf number.

Practical Guidance
Shade netting was identified as the better production environment for productive plant development, earlier flowering, and longer floral stems under the tested semi-arid conditions. Open field conditions favored higher tuberous root production in Babylon. Greenhouse conditions favored higher fresh flower weight in Boy Mick. Dahlia stems were described as hollow, and crop protection from wind and rain was recommended. Variety response to environment was not uniform, reinforcing that production environment and variety choice interact in ways that affect scheduling and yield.

Why This Source Matters
This study contributes the production-environment dimension to this collection's scheduling framework. It demonstrates that where a dahlia crop is grown, whether open field, greenhouse, or shade structure, affects not only final quality but also flowering timing and the allocation between inflorescence production and tuberous root development. For growers managing scheduling across multiple production environments or making infrastructure decisions that affect crop timing, this study provides directly relevant comparative data.

The Knowledge Card summaries in this collection were written by the author based on direct reading of the cited sources. AI tools assisted with retrieval, formatting, and assembly of this collection from the Dahlia Doctor research archive. All curatorial decisions, including source selection, topic organization, and editorial framing, were made by the author.