Dahlia Doctor Research Library: Heat, Temperature Stress, and Hot-Climate Growing

A Curated Knowledge Card Collection

Copyright © 2026 by Steve K. Lloyd
All Rights Reserved

Dahlias look like summer flowers, but they are not built for unlimited heat. They often grow and flower best within moderate temperature windows, even while blooming through the warmest months of the year. Under sustained high temperatures, their photosynthetic systems begin to falter. Buds and flowers can suffer heat injury before the leaves show obvious stress. Roots in black pots, dark containers, or sun-warmed soil can reach damaging temperatures even when the air around the plant still feels tolerable. Flowering itself is temperature-sensitive: when heat crosses the wrong threshold, the developmental program that produces flowers can slow, stall, or stop.

For growers in hot climates, in regions facing more frequent summer heat events, or in greenhouses where temperature control is part of daily production, these responses are practical growing knowledge. The question is not whether heat affects dahlias. The question is where the thresholds are, which systems fail first, and what growers can do to reduce the damage.

This Research Library collection brings together Dahlia Doctor Knowledge Cards on heat stress, root-zone temperature, temperature effects on flowering and crop development, and seasonal timing strategies for warm-region production. The selected studies range from controlled-environment physiology to field-based threshold work to greenhouse forcing trials. Together, they offer the clearest available research-based picture of how dahlias respond to heat, why heat stress can be so difficult to anticipate, and what the evidence suggests growers can do about it.

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, to help you locate the original publication independently.

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. KC-0008 addresses both temperature effects on flowering and photoperiod interactions; it is placed in the temperature and flowering cluster where its heat-threshold findings are most directly useful. KC-0035 contains an internal discrepancy between planting-date labels in the abstract and methods versus the results tables; this entry follows the results-table dates, and the discrepancy is noted in the Why This Source Matters field.

Publication Type

Experimental Research Article

Full Citation

Liu, J. J., Zhang, Y. C., Niu, S. C., Hao, L. H., Yu, W. B., Chen, D. F., & Xiang, D. Y. (2023). Response of dahlia photosynthesis and transpiration to high-temperature stress. Horticulturae, 9(9), 1047.

Study System

Potted dahlia cuttings of 'Tampico' and 'Hypnotica Tropical Breeze' at the blooming stage.

Experimental Context

Controlled high-temperature stress treatments under day/night temperature regimes of 35/30°C and 40/35°C, with 25/20°C as the control. Plants were treated for one or two days and then allowed to recover for seven days at 25/20°C after the two-day treatment.

Experimental Design

Uniform potted cuttings were acclimatized at 25/20°C and then subjected to temperature treatments in an intelligent light incubator under a 14-hour light and 10-hour dark cycle. Measurements included heat injury index, recovery index, stomatal density, stomatal opening, leaf water potential, chlorophyll a, chlorophyll b, carotenoids, chlorophyll fluorescence parameters, net photosynthetic rate, and transpiration rate.

Key Results

High-temperature stress caused leaf edge withering, leaf wilting, flower-bud blackening, and growth halting. Heat injury was generally lower in 'Tampico' than in 'Hypnotica Tropical Breeze'. Under 35/30°C for two days, both varieties recovered to normal condition after seven days at 25/20°C. Under 40/35°C for two days, 'Tampico' had limited new leaf growth after recovery, while 'Hypnotica Tropical Breeze' did not recover. High-temperature stress decreased chlorophyll content, Fv/Fm, transpiration rate, net photosynthetic rate, and leaf water potential. During the same treatment periods, 'Tampico' had higher chlorophyll content, transpiration rate, and stomatal density than 'Hypnotica Tropical Breeze'.

Mechanistic Insight

The study identified differences between the two dahlia varieties in photosynthetic pigment content, stomatal regulation, transpiration ability, and photosynthetic response under high-temperature stress. Higher photosynthetic pigment content, stronger stomatal regulation, and stronger transpiration ability were identified as potential protective mechanisms in the more heat-tolerant variety.

Practical Guidance

Both tested varieties recovered after 35/30°C stress for two days followed by seven days at 25/20°C. Neither variety withstood 40/35°C stress for two days. Cultivar choice affects heat-stress outcome: under identical conditions, 'Tampico' showed less injury and better recovery than 'Hypnotica Tropical Breeze'. Results were obtained under controlled incubator conditions and should be interpreted as physiological evidence rather than direct outdoor production guidelines.

Why This Source Matters

This is one of the few studies in the dahlia literature to directly measure photosynthetic function under acute heat stress and track recovery afterward. The finding that flower buds blackened and growth halted under 35/30°C, while vegetative tissue showed more tolerance, aligns with field observations that dahlia flowers and buds are more heat-sensitive than the rest of the plant. The recovery data, full recovery at 35/30°C and failure at 40/35°C, establish a practical threshold range for understanding when heat events are survivable and when they are not. The cultivar comparison also opens the question of whether heat tolerance is a trait that could be selected in breeding programs, which has longer-term implications for dahlia improvement.

Publication Type

Journal Article

Full Citation

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

Study System

Dahlia spp. grown under open-field commercial production conditions in Southern Brazil.

Experimental Context

Multi-site, multi-season observational field study correlating damage symptoms with maximum air temperature under commercial production conditions.

Experimental Design

Field observations at multiple sites across multiple seasons, correlating recorded maximum air temperatures with observed bud and flower injury symptoms. The study distinguished between temperatures producing damage to reproductive tissues and temperatures producing lethal effects.

Key Results

Irreversible bud and flower injury was observed beginning at approximately 35°C maximum air temperature. Vegetative tissues tolerated temperatures above 40°C without equivalent injury. Reproductive tissues were identified as having a lower upper lethal temperature than vegetative organs.

Mechanistic Insight

Reproductive tissues in dahlia have a narrower thermal tolerance range than vegetative tissues. The differential sensitivity between buds and flowers versus leaves and stems means that heat events damaging enough to abort or blacken flowers may leave the rest of the plant visibly intact, which can obscure the severity of the stress event.

Practical Guidance

In commercial field production in Southern Brazil, shading, irrigation, and planting-date adjustment were identified as the primary management tools for avoiding temperatures at or above 35°C during the flowering period. Growers in other regions should treat the 35°C threshold as field-context evidence, not a universal cutoff, because site conditions, humidity, and crop stage all influence actual injury risk.

Why This Source Matters

This study provides the clearest field-based threshold evidence in the current dahlia literature for the temperature at which reproductive injury becomes irreversible. The finding that buds and flowers are more vulnerable than vegetative tissues helps explain a pattern many growers have observed: a heat event that leaves the plant standing can still end the flowering season for that flush. The multi-site, multi-season observational design also gives this result more generalizability than a single-location controlled study, because it was recorded under the variable conditions of real production rather than a growth chamber. Read alongside KC-0032, which documents the same reproductive vulnerability at the physiological level, the two studies together build a coherent picture of how and why heat injures dahlia reproductive tissues first.

Publication Type

Experimental Research Article

Full Citation

Matsubara, K., Inamoto, K., Doi, M., & Imanishi, H. (2003). Evaluation of heat hardiness of certain geophytes for landscape planting. Horticultural Research (Japan), 2(1), 29–33.

Study System

Sixteen geophytes evaluated for landscape planting under simulated high summer temperature conditions, including dahlia, canna, agapanthus, amacrinum, gladiolus, hedychium, muscari, crocosmia, narcissus, lilium, zephyranthes, liatris, bletilla, and other bulbous or rhizomatous ornamental plants.

Experimental Context

Plants were grown in pots in growth chambers under simulated summer temperature conditions based on ambient outdoor temperatures in Osaka. The study assessed heat hardiness for landscape use under high summer temperature conditions.

Experimental Design

Potted plants were assigned to three temperature conditions: outdoor ambient temperature, ambient temperature plus 5°C, and ambient temperature minus 5°C. Treatments began in early-to-mid July and continued until September 20. After the treatment period, plants were transferred outdoors and observed for survival, emergence, flowering, leaf development, shoot number, plant height, and related growth traits.

Key Results

All dahlia plants died in the ambient plus 5°C treatment. Lilium 'White Angel' also died under this treatment. Several other geophytes did not die but showed reduced growth or delayed development under elevated temperature. Canna grew better under higher temperature conditions. Agapanthus showed reduced leaf unfolding. Amacrinum, gladiolus, and hedychium showed decreased plant height. Muscari and crocosmia showed decreased shoot number.

Mechanistic Insight

Heat hardiness differences among the evaluated geophytes were related to the climatic tendencies of their native regions and to species-level tolerance of high summer temperature. The source also states that actual summer performance is not determined by air temperature alone and may also be affected by drought, soil temperature, disease, insect injury, and other factors.

Practical Guidance

Dahlia was evaluated as having poor heat hardiness under the simulated high-temperature landscape conditions tested. Canna performed well under higher temperatures. Growers selecting geophytes for warm-climate landscapes or for sites that experience extended periods of elevated summer temperature should treat dahlia as a heat-sensitive choice and plan accordingly. Heat hardiness evaluation should also account for additional summer stress factors beyond air temperature alone.

Why This Source Matters

This study places dahlia within a comparative context that is not available in single-species heat-stress work. When dahlia is evaluated alongside fifteen other landscape geophytes, its position becomes clear: it is among the least heat-hardy species tested, with complete plant death at ambient plus 5°C while other species survived with reduced growth. That comparative framing is practically useful for growers who need to select plants for hot-climate landscapes or who want to understand where dahlia sits on a spectrum of ornamental geophyte heat tolerance. The finding also reinforces the threshold evidence from KC-0032 and KC-0143 from a different experimental direction: all three studies point toward dahlia as a plant with a relatively low upper temperature limit compared with other ornamental species.

Publication Type

Experimental Research Article

Full Citation

Schneck, K. K., Boyer, C. R., & Miller, C. T. (2021). Supraoptimal root-zone temperatures affect dahlia growth and development. HortTechnology, 31(6), 667–678.

Study System

Dahlia ×hybrida cultivars from the Dalaya, XXL, and Melody series.

Experimental Context

Potted dahlia greenhouse production using vegetatively propagated plant material. The study addressed reported dahlia decline symptoms including reduced root quality, graying foliage, wilting foliage, and plant death near market stage.

Experimental Design

Seven dahlia cultivars were evaluated across spring greenhouse experiments in two years. Plants were grown for four to five weeks, then root zones were exposed using water baths to control, 35°C, 40°C, 45°C, or 50°C treatments. Five plants per cultivar were assigned to each temperature treatment. Root quality, plant height, flower development, and foliage quality were rated before treatment and weekly for four weeks after treatment.

Key Results

Root ratings declined significantly in both years as temperature treatments increased. Several cultivars showed root-rating decreases after 40°C, 45°C, or 50°C exposure, with significant decreases in XXL Veracruz and XXL Sunset after 45°C and 50°C treatments in the second year. Root ratings increased in later observations for multiple cultivars, indicating recovery after treatment. Plant height was reduced at 50°C for all cultivars in the second year and for most cultivars in the first year. Flower development and foliage ratings were reduced in several cultivars, especially at 50°C. The treatments did not produce uniform plant responses consistent with reported dahlia decline symptoms.

Mechanistic Insight

Supraoptimal root-zone temperature exposure damaged dahlia root systems as shown by reduced root ratings. Subsequent increases in root ratings indicated that some plants recovered after root-zone heat injury. The study did not identify supraoptimal root-zone temperature exposure alone as a primary cause of dahlia decline, which was described as likely involving a more complex combination of physiological or environmental factors.

Practical Guidance

Potted dahlias exposed to elevated root-zone temperatures may show reduced root quality, shorter plant height, delayed or reduced flower development, and lower foliage quality. Root injury from the tested supraoptimal temperatures was sublethal in many plants, but foliage damage or flower delay may still affect marketability. Supraoptimal root-zone temperature exposure alone did not reliably explain greenhouse dahlia decline under the tested conditions.

Why This Source Matters

This study draws attention to root-zone temperature as a distinct heat stress pathway, separate from air temperature effects on leaves and flowers. Container-grown dahlias in black nursery pots, dark-colored raised beds, or greenhouse benches exposed to radiant heat can experience root-zone temperatures well above air temperature, and this study shows that exposure at those levels damages the root system even when the plant above ground appears intact. The recovery data are also practically meaningful: short-duration heat exposure at sublethal levels was survivable for many cultivars, which suggests that the severity of the heat event and the duration of exposure both matter, not just peak temperature alone. The cultivar variation in root ratings further reinforces that heat tolerance is not uniform across the dahlia gene pool.

Publication Type

Conference Proceedings Article

Full Citation

Miller, C. T., Schneck, K., & Martini, N. (2019). Root zone temperature effects on potted dahlia production. XIII International Symposium on Flower Bulbs and Herbaceous Perennials, 1237, 111–116.

Study System

Dahlia ×hybrida vegetative cultivars from the Dalaya, XXL, Karma, and Melody series.

Experimental Context

Greenhouse container production. Supraoptimal root-zone temperature exposure was applied five weeks after transplant.

Experimental Design

Completely randomized design with five root-zone temperature treatments: 18°C, 35°C, 40°C, 45°C, and 50°C. Six replications per cultivar. Root quality was assessed on a 0–4 rating scale with weekly assessments for three weeks after treatment. Statistical mean separation was applied.

Key Results

Elevated root-zone temperature reduced root ratings one week after treatment in most cultivars. Effects were cultivar-dependent. The strongest declines occurred at 45–50°C. Partial recovery was observed after two to three weeks. No complete crop loss occurred under short-duration exposure at the tested temperatures.

Mechanistic Insight

Dahlia roots were less tolerant of high temperatures than shoots. Supraoptimal root-zone temperature weakened root systems, and cultivar genetic differences influenced thermal tolerance. Limited-duration heat stress allowed regenerative recovery in most cultivars tested.

Practical Guidance

Avoid prolonged substrate temperatures at or above 45°C in potted dahlia production. Monitor container growing-medium temperature in late spring and early summer, particularly for containers exposed to direct sun or placed on dark greenhouse surfaces. Account for cultivar-specific sensitivity when managing heat risk. Consider root-zone heat stress as a possible predisposing factor in plants showing unexplained decline symptoms.

Why This Source Matters

Read alongside KC-0050, this study is the earlier publication from the same research group and provides the foundational cultivar-comparative root-rating data that KC-0050 later extended. Together they establish that root-zone temperature is a measurable, cultivar-differentiated stress in potted dahlia production, and that the substrate inside a container can reach temperatures that damage roots well before any visible above-ground symptom appears. For greenhouse growers and anyone producing dahlias in containers in warm climates, these two studies together make the case that managing root-zone temperature is as important as managing air temperature.

Publication Type

Experimental Research Article

Full Citation

Brøndum, J. J., & Heins, R. D. (1993). Modeling temperature and photoperiod effects on growth and development of dahlia. Journal of the American Society for Horticultural Science, 118(1), 36–42.

Study System

Dahlia pinnata 'Royal Dahlietta Yellow', cutting-propagated potted plants.

Experimental Context

Controlled-environment chamber study of temperature and photoperiod effects on growth, morphology, flowering, and tuberous root formation.

Experimental Design

Rooted cuttings were planted in 10-cm pots, held at 20°C for two weeks, pinched to three nodes, and grown with one shoot per plant. One experiment used 25 day-temperature and night-temperature combinations created from chamber temperatures of 10, 15, 20, 25, and 30°C under a 12-hour photoperiod. A second experiment used constant temperatures of 15, 20, 25, and 30°C crossed with photoperiods of 10, 12, 14, 16, 20, and 24 hours. Growth, node count, bud diameter, flowering, lateral shoot traits, tuberous root weight, flower count, flower diameter, canopy traits, and temperature-dependent developmental rates were measured or modeled.

Key Results

Plants flowered under all photoperiods at 15°C and 20°C. At 25°C, plants flowered only under photoperiods of 14 hours or less. At 30°C, no flowering occurred. Lateral shoot count and length decreased as photoperiod decreased from 16 to 10 hours. Tuberous root weight increased as photoperiod decreased. Tuberous roots formed mainly at 15°C and 20°C under 10- and 12-hour photoperiods. No tuberous roots formed at 25°C or 30°C. Flower count and flower diameter decreased as average daily temperature increased. Node number below the first flower increased as average daily temperature increased. Modeled optimum temperatures were 24.6°C for leaf-pair unfolding, 22.4°C for development from pinch to visible bud, and 24.4°C for development from visible bud to flower.

Mechanistic Insight

Temperature-dependent leaf and flower development rates followed asymmetrical peak-shaped response curves. Short photoperiods and lower temperatures promoted tuberous root formation while reducing vegetative and reproductive shoot growth. Day-night temperature difference was positively related to primary shoot elongation over most of the tested temperature range.

Practical Guidance

For the tested cultivar under controlled conditions, temperatures at or above 25°C suppressed flowering under longer photoperiods, and no flowering occurred at 30°C regardless of photoperiod. Temperatures of 15°C to 20°C with 12- to 14-hour photoperiods produced fast-developing plants with good flower counts and adequate plant height. These results were obtained from a controlled potted-crop model and should not be applied as absolute outdoor production thresholds, but they establish the direction and approximate range of temperature effects on flowering in this species.

Why This Source Matters

The finding that no flowering occurred at 30°C in a controlled-environment study of a named cultivar is one of the most directly cited temperature results in the dahlia literature, and it belongs in this collection as foundational evidence for understanding why dahlias stop flowering under sustained summer heat. The modeled developmental rates also provide a quantitative framework for thinking about how temperature affects crop timing: development from visible bud to flower had an optimum near 24°C, meaning that temperatures above that optimum slow the final stage of flowering rather than accelerating it to completion. That counterintuitive result, heat speeding some processes while blocking others, is important context for growers who observe heat-stressed plants that seem to stall just before flowering.

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 'Kolchelsee' and 'Park Princess'.

Experimental Context

Greenhouse forcing of stored tuber clumps from January to June under controlled environmental conditions.

Experimental Design

Randomized complete block design with factorial evaluation of fertilizer, temperature, light intensity, and photoperiod treatments. Fifteen plants were used per treatment. Treatments included multiple temperature regimes, light intensity levels, and photoperiod lengths, evaluated in combination with fertilization.

Key Results

Fertilization was required for full flowering and improved plant quality. Optimal plant quality was achieved at 25°C/16°C day/night temperatures. Higher temperatures accelerated flowering but reduced plant quality. A 50% reduction in light intensity increased plant height and delayed flowering. An 8-hour photoperiod reduced flowering percentage and overall plant quality.

Mechanistic Insight

Temperature altered the rate of floral differentiation and vegetative growth. Reduced light increased stem elongation. Short photoperiod interfered with normal floral development and reduced flowering percentage. The interaction of these factors determined both the timing and quality of the forced crop.

Practical Guidance

For spring greenhouse forcing of tuberous-rooted dahlias, continuous fertilization, high light intensity, and approximately 25°C/16°C day/night temperatures produced the best plant quality in this study. Avoid short days and heavy shading during forcing. Temperature can be used to manage crop timing, but higher temperatures that accelerate flowering may reduce the quality of the finished plant.

Why This Source Matters

This study contributes a finding that is not captured by the heat-injury cards in this collection: heat can accelerate the flowering timeline while simultaneously reducing the quality of the flowers and plant produced. That distinction matters for growers and greenhouse operators who might assume that warmer conditions simply move a crop forward on the schedule. The 25°C/16°C optimum identified here also provides a reference temperature for dahlia forcing quality that complements the broader threshold data in KC-0008, which found no flowering at 30°C. Together the two studies bracket a practical temperature range: above roughly 25°C, crop quality declines even as development may accelerate; above 30°C, flowering may stop entirely. The 1977 date also places this finding in the historical arc of controlled-environment dahlia research, predating the modeling work of KC-0008 by sixteen years and establishing that the quality-versus-speed tradeoff under heat was documented in forced production decades before modern growth-chamber studies confirmed the threshold.

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.

Experimental Context

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

Experimental Design

Randomized complete block design with four sowing-date treatments and four replications per treatment, with 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 and linked stronger plant growth, larger flower size, longer blooming period, and higher seed yield with the sowing treatment that germinated fastest. Low temperatures after October sowing were described as restricting vegetative growth before a later temperature rise allowed flowering.

Practical Guidance

For the tested Rawalpindi conditions, the source recommended 25 September as the best sowing time. The source stated that dahlia flower availability can be managed in advance by adjusting sowing time. These results are specific to the autumn-winter production season and climate of Rawalpindi and should not be transferred directly to other regions without adjustment.

Why This Source Matters

This study provides direct evidence that sowing timing in a warm-climate location shapes not just when flowering occurs but how well the plant performs overall: flower size, blooming period, and seed yield all responded significantly to sowing date. The mechanism the authors identified, germination at an optimal temperature producing a better-established plant before cooler or hotter conditions arrive, is the core scheduling principle behind warm-region dahlia production. For growers in climates with hot summers and mild winters, this study is a useful model for thinking about why timing the crop to establish before peak heat, rather than during it, is worth the planning effort.

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, grown from rooted cuttings for tuber production.

Experimental Context

Field evaluation under low hill conditions in Himachal Pradesh, India, comparing three planting-date treatments across five cultivars.

Experimental Design

Factorial randomized block design with five cultivars and three planting-date treatments, three replications, 15 treatment combinations, and 45 experimental plots. Rooted cuttings were planted at 45 cm × 45 cm spacing with nine plants per plot. 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

Suryadev had the greatest mean plant height and internodal length. Matungini had the greatest mean plant spread, number of tubers per plant, and tuber length. Giani Zail Singh had the greatest mean tuber diameter. Anarkali had the greatest mean tuber weight per plant and tuber yield per plot. In the results tables, October 15 planting produced the highest mean number of tubers per plant, tuber diameter, tuber length, tuber weight per plant, and tuber yield per plot.

Mechanistic Insight

The source attributes cultivar differences in plant traits and tuber production to genetic traits, environmental conditions, soil composition, and cultivar responses to local environmental circumstances. Planting-date effects were not mechanistically separated from seasonal temperature and photoperiod changes in the article.

Practical Guidance

October 15 was identified as the most suitable planting date for tuber production and tuber characteristics under the reported low hill conditions. Among the five cultivars, Anarkali performed best for tuber weight and tuber yield per plot, Matungini for tuber number and tuber length, and Giani Zail Singh for tuber diameter. Results are specific to the low hill conditions and growing season reported.

Why This Source Matters

In the context of this collection, this study illustrates that planting date is not just a scheduling convenience but a production variable with measurable consequences for how well a crop develops. In low hill conditions where summer temperatures can stress dahlias, the difference between an October 15 planting and a later planting translated directly into tuber yield outcomes across five cultivars. The implication for hot-climate growers, that getting plants established during a favorable temperature window matters more than the specific calendar date, is consistent with the timing principle supported by KC-0001 and KC-0863. This source also carries a data integrity note: the abstract and methods section list September 15, October 15, and November 15 as the three planting-date treatments, while the results tables report October 15, November 15, and December 15. This entry follows the results-table dates because they are attached to the reported production data. Readers who obtain the original source should note this internal discrepancy.

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 production of early summer flowering pot plants.

Experimental Context

Seed-grown dwarf dahlia plants were evaluated under different sowing periods for production of early summer flowering pot plants used in green space decoration.

Experimental Design

Monofactorial randomized block experiment with sowing period as the experimental factor. Four variants were tested: March 5 in an artificially heated greenhouse, March 15 in an artificially heated greenhouse, March 25 in an artificially heated greenhouse, and April 15 in open field as the witness variant. Four replications were used per variant. 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 witness variant recorded the lowest values across all three traits. Plant height for the March 15 and March 25 greenhouse sowings was significantly higher than the witness variant. Average flower surface was highest in the March 25 greenhouse variant and significantly positive compared with the witness. 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. Controlled temperature conditions during establishment supported better early plant development than open-field sowing in April.

Practical Guidance

For vigorous seed-grown Dahlia variabilis plants with larger flowers and more seeds, the source recommends sowing during March 15 to 25 in heated greenhouses where possible. These results are specific to the Romanian climate and spring production context and should be adapted to local conditions.

Why This Source Matters

This study closes the timing cluster with evidence from a European spring production context, complementing the autumn-sowing evidence from KC-0001 and the planting-date evidence from KC-0035. The consistent finding across all three studies is that establishing dahlia plants during favorable temperature conditions, before heat stress arrives or after the worst of it has passed, produces measurably better plants than sowing or planting at suboptimal times. Here, the mechanism is explicit: the source attributes the advantage of March greenhouse sowing to stable, warm temperatures during germination and early establishment. That finding connects the timing cluster back to the physiological evidence in the first two clusters: dahlias develop best within a specific temperature window, and the practical strategy for hot-climate growers is to engineer the crop calendar so that establishment and peak flowering fall within that window rather than outside it.

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.