Dahlia Doctor Research Library: Growth Regulators in Dahlia Production

A Curated Knowledge Card Collection 

Copyright © 2026 by Steve K. Lloyd. 
All Rights Reserved.

Dahlia growers usually think about growth in practical terms: tall or compact plants, strong or weak cuttings, early or late flowers, and tubers that either size up well or disappoint at the end of the season. Plant growth regulators sit behind many of those outcomes. Some are applied deliberately as sprays, drenches, dips, or soaks. Others are internal hormones that help determine whether a dahlia keeps stretching upward, shifts energy into flowering, forms roots on a cutting, or begins thickening tuberous roots.

This Research Library collection brings together Dahlia Doctor Knowledge Cards on growth regulators in dahlias. The selected studies include chemical height-control work with paclobutrazol, ancymidol, uniconazole, flurprimidol, daminozide, and chlormequat; auxin studies on rooting cuttings; gibberellin studies on stem elongation and growth reactivation; and physiological work on the hormonal control of tuberization. Together, they show that "growth regulator" is not one simple category. The same treatment may reduce height, alter flowering, change branching, affect tuberous-root development, or produce different results depending on cultivar, dose, timing, and production system.

For growers and breeders, the value of this collection is not that it provides a single recipe. It does not. Instead, it shows why dahlias respond so strongly to hormonal signals and why production goals must come first. A treatment that helps finish a compact potted plant may not serve the same purpose as a rooting dip for cuttings, a gibberellin spray for growth reactivation, or a physiological signal involved in tuber formation. The research below helps separate those uses, so growth regulators can be understood as tools with tradeoffs rather than shortcuts.

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. Several retardant studies address both compact growth and tuberous-root effects within the same experiment; these are placed in the retardant cluster and their tuber-related findings are noted within their Key Results fields.

Publication Type

Peer-reviewed Journal Article

Full Citation

Whipker, B. E., Eddy, R. T., & Hammer, P. A. (1995). Chemical growth retardant application to tuberous-rooted dahlias. HortTechnology, 5(3), 220–222.

Study System

Tuberous-rooted Dahlia variabilis cultivars 'Golden Emblem' and 'Red Pigmy'

Experimental Context

Greenhouse container-production height-control study.

Experimental Design

Media drench applications of ancymidol, paclobutrazol, and uniconazole; 10 replications; ANOVA with LSD comparison.

Key Results

Ancymidol at 1.5–2.0 mg reduced total height by about 45%. Uniconazole was moderately effective. Paclobutrazol response was cultivar-dependent. Ancymidol delayed flowering by about five days.

Mechanistic Insight

Height reduction occurred primarily through suppression of inflorescence elongation rather than canopy reduction.

Practical Guidance

In greenhouse container production, ancymidol and uniconazole controlled height in tested cultivars, but response was cultivar-specific and flowering delay should be considered. Chemical use should follow current label and regulatory constraints.

Why This Source Matters

This study established baseline efficacy data for ancymidol, paclobutrazol, and uniconazole as drench treatments in container-grown tuberous-rooted dahlias and identified that height control in this crop operates primarily through inflorescence stem suppression rather than canopy reduction. The finding of cultivar-dependent paclobutrazol response was an early signal that chemical height control in dahlias cannot be treated as a uniform prescription across genotypes.

Publication Type

Journal Article

Full Citation

Whipker, B. E., & Hammer, P. A. (1997). Efficacy of ancymidol, paclobutrazol, and uniconazole on growth of tuberous-rooted dahlias. HortScience, 32(4), 671–673.

Study System

Container-grown tuberous-rooted dahlia cultivars 'Golden Emblem' and 'Red Pigmy'

Experimental Context

Greenhouse production of potted tuberous-rooted dahlias under natural daylength, evaluating substrate drench applications of plant growth regulators for height control.

Experimental Design

Dormant tubers potted in 1.5-L containers; substrate drenches of ancymidol (0.5–8 mg a.i./pot), paclobutrazol (1–16 mg a.i./pot), and uniconazole (0.125–5 mg a.i./pot) applied 13 days after potting; completely randomized design with single-plant replicates; measurements of canopy height, total height, plant diameter, inflorescence height and diameter, and days to flowering; GLM with LSD at P ≤ 0.05.

Key Results

All three PGRs reduced total and canopy height in a dose-dependent manner. Total height reductions in 'Red Pigmy' exceeded 21%. Inflorescence height was reduced by more than 29% at effective doses. Higher doses caused excessive stunting and leaf distortion. Ancymidol delayed flowering at all doses. Paclobutrazol and uniconazole generally did not delay flowering within optimal ranges. Plant diameter was reduced by all treatments. Inflorescence diameter was reduced at higher ancymidol and uniconazole doses.

Mechanistic Insight

Height control was achieved primarily through reduction of inflorescence height rather than canopy height, indicating that shoot elongation processes in dahlia are particularly sensitive to these growth regulators.

Practical Guidance

Use paclobutrazol at 2–8 mg a.i./pot, uniconazole at 0.25–1 mg a.i./pot, or ancymidol at 0.5 mg a.i./pot for marketable height control in 1.5-L pots. Avoid higher doses to prevent excessive stunting, leaf distortion, reduced inflorescence diameter, and flowering delay. Select rate based on cultivar vigor and desired finished height.

Why This Source Matters

This paper is the most detailed dose-response study for these three retardants in tuberous-rooted dahlia container production. It provides the quantitative rate guidance that KC-0793 established in qualitative terms and adds inflorescence diameter and flowering-delay data that are directly relevant to production decisions. The identification of safe working ranges for each chemical, and the distinction between ancymidol's flowering-delay effect and the relative neutrality of paclobutrazol and uniconazole on that trait, makes this the practical reference for greenhouse growers managing compact dahlia production.

Publication Type

Conference Proceedings Article

Full Citation

McCall, I., Buhler, W., Whipker, B. E., & Krug, B. (2008). Flurprimidol preplant tuber soaks for dahlia growth control. X International Symposium on Flower Bulbs and Herbaceous Perennials, 886, 393–396. 

Study System

Greenhouse-forced 'Purple Gem' tuberous-rooted dahlia (Dahlia variabilis Willd.)

Experimental Context

Preplant tuber soak growth regulator evaluation under greenhouse forcing conditions.

Experimental Design

Completely randomized design; seven flurprimidol concentrations (0–40 mg/L); 10-minute soak; n=5 single-plant replicates; regression and linear-plateau modeling.

Key Results

A 26% reduction in plant height was achieved at 11.6 mg/L. A 22% reduction in canopy height was achieved at 20 mg/L. Plant diameter was not significantly changed. Flowering was delayed 11–16 days at 20–40 mg/L.

Mechanistic Insight

Height control was primarily due to reduced inflorescence elongation rather than canopy reduction.

Practical Guidance

Preplant soaks of approximately 11.6–20 mg/L reduce height without affecting plant diameter. Concentrations at or above 20 mg/L delay flowering excessively. An economic comparison with drench applications is advisable before adopting this method.

Why This Source Matters

This study covers a delivery method not addressed in the drench-focused KC-0793 and KC-0794 studies. Treating the tuber before planting, rather than the growing medium after establishment, represents a distinct point of intervention in the production timeline. The data show that preplant flurprimidol soaks can reduce inflorescence elongation at concentrations that do not affect plant diameter, but that the flowering delay at higher concentrations limits the usable range. The linear-plateau modeling approach also provides a more precise description of the dose-response relationship than simple comparison of treatment means.

Publication Type

Experimental Research Article

Full Citation

Pichardo-Ruiz, F. D., Villegas-Monter, Á., Hernández-Livera, A., & Colinas-León, M. T. (2003). Morphological changes in dahlia (Dahlia pinnata Cav.) plants treated with paclobutrazol. Revista Chapingo. Serie Horticultura, 9(1), 151–161. 

Study System

Dahlia pinnata Cav. clone CP/123, a tall clone with Mexican pink flowers, grown from tuberous roots in greenhouse.

Experimental Context

Greenhouse foliar paclobutrazol treatments applied every 14 days for seven applications.

Experimental Design

Latin square design with five treatments and five replications of two experimental units each; 50 total plants. Paclobutrazol, reported by the source as a 0.4% active-ingredient formulation, was applied foliarly at 0, 50, 100, 200, and 400 ml·liter⁻¹ every 14 days for seven applications. Evaluated variables included plant height, stem diameter, node number, internode length, chlorophyll a, chlorophyll b, total chlorophyll, tuberous root weight, tuberous root volume, and tuberous root number. 

Key Results

The 400 ml·liter⁻¹ treatment produced the shortest plants, with the source reporting 45.30 cm in the summary and 42.89 cm in the treatment table. Paclobutrazol reduced internode length, with stronger reductions at higher concentrations. Total chlorophyll was highest at 400 ml·liter⁻¹. Tuberous root weight and volume increased at the higher concentrations, while tuberous root number increased only at 200 ml·liter⁻¹. Stem diameter response was not clearly attributable to paclobutrazol.

Mechanistic Insight

Paclobutrazol inhibits gibberellin production in subapical meristems by preventing the oxidation of kaurene to kaurenoic acid, reducing cell division and expansion and limiting growth. Increased tuberous root weight is associated with a possible modification in carbohydrate distribution toward roots when gibberellin activity is inhibited.

Practical Guidance

Under the reported greenhouse conditions, repeated foliar applications of the source’s paclobutrazol formulation produced compact dahlia plants with shorter internodes, higher total chlorophyll, and increased tuberous root weight. Because the source reports rates in ml·liter⁻¹ of formulation, these concentrations should not be converted casually or transferred directly into practice without checking the original product, active ingredient, label, and current regulatory constraints. 

Why This Source Matters

This study is notable for documenting not only architectural changes — shorter internodes, more compact form — but also changes in chlorophyll content and tuberous root biomass in response to repeated paclobutrazol applications. The tuberous root weight response connects the retardant cluster to the tuberization physiology covered later in this collection: when gibberellin activity is suppressed, assimilate partitioning appears to shift toward storage organs. That link between applied retardant use and root development adds a dimension beyond simple height control. The unusual formulation-based rate reporting also makes this a source where the biological response is more transferable than the exact application rate. 

Publication Type

Experimental Research Article

Full Citation

Pudelska, K., & Witek, A. (2005). Wpływ daminozydu na wzrost i walory dekoracyjne wybranych odmian dalii ogrodowej (Dahlia cultorum Thorsr. et Reis.) [Effect of daminozide application on growth and decorative value of dahlia (Dahlia cultorum Thorsr. et Reis.) cultivars]. Zeszyty Problemowe Postępów Nauk Rolniczych, 504, 681–687. 

Study System

Dahlia × cultorum cultivars 'Krynica', 'Gea', and 'Red Pigmy' grown from green cuttings in containers.

Experimental Context

Container production trial with foliar daminozide applications, plants pinched and grown outdoors beside a greenhouse.

Experimental Design

Randomized block experiment; plants sprayed once with daminozide as B-Nine 85 SP at 2,125, 4,250, or 6,375 mg·dm⁻³ after lateral shoots reached about 2 cm; evaluated traits included inflorescence number, inflorescence diameter, peduncle length, lateral shoot number, plant diameter, and plant height.

Key Results

Daminozide reduced plant height in all tested cultivars. The highest concentration produced plants 13.7–18.8% shorter and 15–25% narrower than untreated controls. Higher concentrations increased inflorescence number in 'Gea' but did not significantly affect abundant flowering in 'Krynica' or 'Red Pigmy'. Daminozide shortened peduncles and reduced inflorescence diameter in all cultivars. No significant effect on branching was found.

Mechanistic Insight

The source does not describe a biochemical pathway for daminozide action, but it shows a functional growth-regulation pattern: higher daminozide concentrations restricted vertical growth and plant diameter, shortened inflorescence peduncles, and reduced inflorescence diameter without significantly changing branching. The response depended on cultivar and concentration, with 'Gea' showing increased inflorescence number at higher concentrations while 'Krynica' and 'Red Pigmy' did not.

Practical Guidance

In this container-production trial, a single foliar spray of daminozide at 4,250 or 6,375 mg·dm⁻³ reduced plant height, narrowed plant diameter, improved compact habit, and shortened inflorescence peduncles in 'Gea', 'Krynica', and 'Red Pigmy'. The source concluded that all three cultivars were suitable for container plantings after daminozide treatment at these concentrations, but practical use should still follow current product labels and regulations.

Why This Source Matters

This study documents cultivar-specific variation in daminozide response across three dahlia cultivars in container production, including a case where increased inflorescence number occurred in one cultivar but not the other two. The peduncle shortening and inflorescence diameter reduction findings are practically significant: a retardant that produces compact plants may simultaneously alter the flower presentation in ways that affect ornamental value. The cultivar-response data reinforce the broader theme of this collection — that PGR outcomes depend on which cultivar is treated, not only on which chemical is applied.

Publication Type

Journal Article

Full Citation

Akbar, P. I., Mohan, B., & Kumar, V. (2011). Effect of chlormequat spraying on vegetative growth and flowering of dahlia (Dahlia variabilis L.). Asian Journal of Horticulture, 6(1), 247–248. 

Study System

Dahlia variabilis L. grown from rooted cuttings in pots.

Experimental Context

Pot experiment under winter-season conditions; foliar sprays applied twice at 20 and 40 days after transplanting.

Experimental Design

Completely randomized block design with three replications; chlormequat treatments at 1500, 2500, 3500, 4500, and 5500 ppm plus control; growth and flowering parameters measured.

Key Results

Chlormequat reduced plant height and leaf area, with the strongest reduction at higher concentrations. Stem diameter and branches per plant increased, with maximum branching at 4500 ppm. Leaf number increased compared with control. The 3500 ppm treatment resulted in earliest flowering. Highest flower number occurred at 5500 ppm. Largest flower diameter occurred at 4500 ppm.

Mechanistic Insight

Growth retardation was associated with reduced cell division and elongation in the sub-apical meristem and a shift toward compact growth with increased branching and stem thickness.

Practical Guidance

In this winter pot experiment, chlormequat shifted dahlia architecture toward compact growth and altered flowering traits, but concentration choice and use should be constrained by cultivar, production goal, application timing, and current chemical-use regulations.

Why This Source Matters

This study is distinctive within the retardant cluster for documenting that chlormequat not only reduced plant height but also increased branching and altered flower number and diameter in a concentration-dependent pattern. The finding that maximum branching, earliest flowering, and largest flower diameter each occurred at different concentrations illustrates that production goals — compactness, flower timing, or flower quality — cannot all be optimized simultaneously by a single treatment rate. That tradeoff is central to the practical guidance framework for PGR use in dahlias.

Publication Type

Thesis/Dissertation

Full Citation

Suma, B. (1993). Effect of growth retardants on growth, flowering, vase-life and tuber formation of dahlia (Dahlia variabilis Desf.) propagated through cuttings (Master's thesis). Kerala Agricultural University, Vellayani, India. 

Study System

Dahlia variabilis cv. Formal Decorative propagated through rooted cuttings.

Experimental Context

Pot experiment evaluating foliar sprays of Alar (daminozide) and CCC (chlormequat) on vegetative growth, flowering, vase-life, and tuberous root formation.

Experimental Design

Rooted cuttings transplanted to 12-inch earthenware pots; Alar applied at 500, 1000, 2000, and 4000 ppm; CCC applied at 250, 500, 1000, and 2000 ppm; completely randomized design; second spray applied 15 days after the first.

Key Results

Alar markedly reduced plant height; CCC did not show appreciable height reduction. Alar at 1000 and 4000 ppm increased branch number over control. Alar increased leaf number more clearly than CCC. CCC was superior to Alar for total chlorophyll content. Alar delayed flower bud appearance by 3.9 to 5.9 days, while CCC induced earlier flowering by 8 to 10 days. Alar improved flower size, floret number, flower longevity, vase-life, and fresh weight of tuberous roots. Maximum tuberous root production was recorded with Alar at 4000 ppm.

Mechanistic Insight

Alar-related height reduction was attributed to reduced internodal length associated with inhibition of cell division and elongation in the subapical meristem.

Practical Guidance

Alar treatments produced shorter plants and increased fresh tuberous root weight under the pot conditions tested. CCC treatments produced earlier flowering but did not appreciably reduce plant height.

Why This Source Matters

This study is one of the few in this collection to evaluate effects on vase-life alongside growth, flowering, and tuberous root traits in the same experiment. The contrast between Alar and CCC is particularly useful: height reduction, tuberous root weight, and flowering delay all favored Alar, while earlier flowering favored CCC, and neither chemical was uniformly superior across all measured traits. That kind of within-experiment comparison across multiple endpoints — growth, flower timing, flower longevity, tuber weight — provides a more complete picture of retardant tradeoffs than single-trait studies.

Publication Type

Experimental Research Article

Full Citation

Read, P. E., Dunham, C. W., & Fieldhouse, D. J. (1972). Increasing tuberous root production in Dahlia pinnata Cav. with SADH and chlormequat. HortScience, 7(1), 62–63. 

Study System

Vegetatively propagated Dahlia pinnata Cav. cultivars 'Nita', 'Celebrity', 'Joe Davis', and 'Arthur Godfrey'.

Experimental Context

Foliar growth-retardant treatments tested under short-day and long-day conditions to evaluate effects on tuberous root formation, yield, crown weight, and subsequent plant quality.

Experimental Design

Rooted cuttings grown in pots and treated with foliar sprays of SADH or chlormequat at specified concentrations; long-day experiments used night interruption lighting; short-day experiments used natural short-day conditions; tuberous roots harvested after defined growth periods and evaluated for number, diameter, crown weight, and sprouting performance after storage.

Key Results

SADH at 2500 ppm and chlormequat increased tuberous root number and size under short-day conditions. In 'Nita', treated plants formed tuberous roots under long-day conditions when untreated controls produced no fleshy roots at the first inspection. In short-day experiments, SADH increased tuberous root number, root diameter, and crown weight in 'Celebrity' and increased crown weight in 'Joe Davis'. Stored 'Celebrity' crowns from SADH-treated plants averaged more buds and produced healthy plants, while nontreated crowns in that experiment did not produce plants. In 'Arthur Godfrey' under long-day conditions, treatment differences were not statistically significant, although trends toward increased root diameter and crown weight were reported.

Mechanistic Insight

Growth-retardant treatments appeared to alter the tuberous root response to photoperiodic conditions. The source states that tuberous root production may not be a simple direct response to day length and may result from a combination of physiological effects associated with short-day growing conditions.

Practical Guidance

SADH treatments increased tuberous root production and improved pot-root quality under the tested conditions, including in cultivars that normally produced few or poor-quality tuberous roots. The source identifies potential commercial value for producing more and better quality dahlia pot-roots.

Why This Source Matters

This study closes the retardant cluster with a finding that bridges growth regulation and tuberization physiology: applied retardants can shift tuberous root formation under conditions where untreated plants produce little or no fleshy root tissue, including under long days. The cultivar-specific nature of the response — dramatic in some cultivars, nonsignificant in others — reinforces the broader pattern seen throughout this cluster. KC-0046 also connects directly to the hormonal tuberization research in the final cluster of this collection, where the mechanisms behind photoperiod and assimilate partitioning are addressed at the physiological level.

Publication Type

Experimental Research Article

Full Citation

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.

Study System

Dahlia × hybrida cultivar 'Vassio Meggos'; heel cuttings excised from sprouted tuberous roots; herbaceous cuttings without heel excised from tender terminal shoots.

Experimental Context

Cuttings prepared from cold-stored tubers; rooted over a five-week observation period.

Experimental Design

Two-factor randomized complete block design with three replications and ten cuttings per replication; cutting bases dipped for 5 seconds in distilled water control or IBA solutions at 500, 1000, 1500, 2000, 2500, or 3000 mg L⁻¹; measurements included cutting survival, root initiation, root count, root length, rooting percentage, callus formation, unrooted callus-free cuttings, root dry weight, shoot dry weight, and root:shoot ratio.

Key Results

Mean cutting survival exceeded 85% for most IBA treatments except control and 3000 mg L⁻¹. The 500 mg L⁻¹ treatment recorded the highest mean survival. Root initiation occurred earlier in IBA-treated cuttings than untreated cuttings, with 1500 mg L⁻¹ producing root initiation at 17.5 days. Root count and root length increased with IBA treatment, with high values at 2500 mg L⁻¹. Heel cuttings produced higher root count, longer roots, slightly higher rooting percentage, and fewer unrooted callus-free live cuttings than cuttings without heel. Rooting percentage was highest at 2500 mg L⁻¹ and was statistically similar to 1500 and 2000 mg L⁻¹. Root and shoot dry weights were highest at 2500 mg L⁻¹.

Mechanistic Insight

Exogenous IBA was associated with improved rooting and growth traits. Callus formation at the basal cut end may delay root initiation rather than act as a precursor to wound-induced rooting. Adventitious root formation involves dormant pre-formed root initials and wound-induced rooting, with auxin stimulating rhizogenesis. Short tuberous roots were observed in heel cuttings.

Practical Guidance

For uniform rooting, shoots from sprouted tubers treated with 1500 mg L⁻¹ IBA produced early rooting with better quality roots and shoots. The source advises dahlia nursery growers to undertake replicated trials before mass multiplication to determine varietal response to different IBA concentrations.

Why This Source Matters

This is the most recent and methodologically detailed IBA study in this collection, and the only one to directly compare heel cuttings against non-heel cuttings alongside an IBA dose-response series. The finding that callus formation may delay rather than facilitate rooting challenges a common assumption and has direct implications for how cutting preparation and timing are managed. The identification of a usable range rather than a single optimal dose — with 1500, 2000, and 2500 mg L⁻¹ producing statistically similar rooting percentages — is practical guidance grounded in experimental replication.

Publication Type

Journal Article

Full Citation

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. 

Study System

Dahlia variabilis L. cultivars Kenya Blue and Kenya Yellow.

Experimental Context

Auxin-mediated rooting of stem cuttings under mist chamber conditions.

Experimental Design

Factorial CRD using IBA and NAA at multiple concentrations and combinations.

Key Results

IBA at 1000 ppm maximized rooting percentage. IBA at 500 ppm maximized root length. The combination of IBA and NAA at 250 ppm minimized days to rooting.

Mechanistic Insight

Auxin-enhanced adventitious rooting via carbohydrate translocation and root primordia induction.

Practical Guidance

Under the tested mist-chamber conditions, IBA at 500–1000 ppm supported robust rooting, while combined IBA and NAA reduced time to rooting. 

Why This Source Matters

This study extends the auxin cluster by documenting NAA alongside IBA and showing that a combined IBA and NAA treatment can reduce time to rooting even when individual applications of either hormone at the same concentration do not. The two cultivars tested — Kenya Blue and Kenya Yellow — also provide a direct comparison of genotype response under identical treatment conditions, reinforcing the cultivar-sensitivity theme that appears across multiple clusters in this collection. Read alongside KC-0878 (above), this study helps establish that auxin dose and auxin combination both influence rooting outcome in dahlia cuttings.

Publication Type

Journal Article

Full Citation

Mittal, S. P. (1967). Studies on the effect of gibberellin on growth and flowering of dahlia. Indian Journal of Horticulture, 24(3–4), 182–184. 

Study System

Seed-grown dahlia plants in earthen pots.

Experimental Context

Foliar gibberellin application before anthesis under pot-culture conditions.

Experimental Design

Five gibberellin concentrations from 50 to 500 ppm applied twice at vegetative stages; control included; measurements of height, internodes, branching, fresh and dry weight, days to first flower.

Key Results

Gibberellin increased plant height through internode elongation up to 300 ppm. The 500 ppm treatment reduced elongation. Internode number decreased. Branching increased. Concentrations of 200 ppm and higher increased biomass. Concentrations of 100–200 ppm advanced flowering by about 7–9 days.

Mechanistic Insight

Gibberellin altered stem elongation, internode length, branching, biomass, and flowering time in a dose-dependent manner.

Practical Guidance

In this pot experiment, moderate gibberellin concentrations advanced flowering and increased height, but direct use should be interpreted cautiously because response varied by dose and excessive concentrations reduced elongation.

Why This Source Matters

This 1967 study is one of the earliest documented experiments on exogenous gibberellin effects in dahlia and provides a baseline for understanding GA-driven elongation and flowering-time responses. The dose-response pattern — where moderate concentrations advanced flowering and increased height but very high concentrations reversed the elongation response — is relevant context for interpreting the more recent KC-0813 (below), which uses GA₃ to reactivate growth after paclobutrazol suppression. Historically, it also places gibberellin research in dahlias within a longer trajectory of applied plant physiology work that predates molecular characterization of the relevant biosynthetic pathways.

Publication Type

Journal Article

Full Citation

Alkaç, O. S., Öndeş, E., Temir, R., Tuncel, E., & Işbilir, M. E. (2023). Büyüme geciktirici ile yetiştirilen Dahlia bitkilerinin giberellik asit ile büyümesinin hızlandırılması [Acceleration of the growth of Dahlia (Dahlia sp.) plants grown with a growth retardant with gibberellic acid]. Turkish Journal of Agriculture - Food Science and Technology, 11(1), 104–111.

Study System

Dahlia (Dahlia sp.) cultivar 'Figaro Violet Shade' grown from seed under greenhouse conditions.

Experimental Context

Greenhouse seedling and potted plant production with sequential application of growth retardant and growth-promoting hormone.

Experimental Design

Two-stage greenhouse experiment with three replications. Seeds were soaked for 2 hours at room temperature in paclobutrazol at 0, 25, 50, or 100 ppm. Seedlings were later treated with foliar GA₃ at 0, 100, or 200 ppm after potting. Growth, flowering, biomass, and root parameters were measured across seedling and potted-plant stages. 

Key Results

At the seedling stage, 25 ppm paclobutrazol produced the highest germination rate and slightly greater early seedling height than the control, while higher paclobutrazol doses reduced seedling growth. In later potted plants derived from paclobutrazol-treated seed, 50 ppm paclobutrazol produced the highest numerical plant height and stem diameter, although most later plant-growth traits under paclobutrazol alone were not statistically significant; flower number, root wet weight, and root length showed significant treatment effects. GA₃ at 100 ppm significantly increased plant height and stem diameter, while 200 ppm GA₃ produced the highest flower number and the smallest flower diameter. In the combined treatments, 50 ppm paclobutrazol plus 100 ppm GA₃ produced the highest plant height, but the strongest responses differed by trait. 

Mechanistic Insight

Paclobutrazol suppresses vegetative growth by inhibiting gibberellin biosynthesis, reducing cell elongation. GA₃ application counteracts this suppression by restoring gibberellin-mediated growth processes, increasing stem elongation and developmental rate.

Practical Guidance

In this greenhouse study, the authors concluded that 25 ppm paclobutrazol could be useful for seedling height control and that 100 ppm GA₃ could help counter possible retarding effects after transplanting. Because responses differed by trait, and because several later plant-growth effects were not statistically significant, practical use should be treated as experimental and constrained by cultivar, production goal, product label, and current regulations. 

Why This Source Matters

This study tests whether growth suppression from paclobutrazol can be partly countered by subsequent GA₃ application, offering a sequential growth-regulation model rather than a single-point treatment. The results are consistent with the expected GA pathway relationship: paclobutrazol suppresses gibberellin-linked elongation, while GA₃ can restore some growth traits after transplanting. The study is most useful as evidence that sequential growth suppression and growth reactivation can be tested in dahlias, not as a universal production recipe. 

Publication Type

Journal Article

Full Citation

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.

Study System

Dahlia cv. 'Choot Hashani'; budless leaf cuttings; intact plants under long-day and short-day conditions.

Experimental Context

Greenhouse conditions; long days (18 h) vs. short days (9 h); repeated GA, ABA, CEPA, and BA treatments; anatomical and biochemical analyses.

Experimental Design

Rooted budless leaf cuttings treated with growth regulators under LD and SD; measurement of organ fresh and dry weights; positional cutting experiments; assay of endogenous ABA-like inhibitors; anatomical sectioning of petiole bases and roots.

Key Results

GA reduced tuber weight and root growth. ABA promoted tuberous root growth. Short days increased endogenous ABA-like inhibitors. Lower-node cuttings had greater tuberization. Tuberization was associated with interfascicular cambial activity.

Mechanistic Insight

GA inhibits tuberization by altering assimilate allocation and sink position. ABA enhances translocation to tuberous roots. Short-day-induced ABA-like inhibitors correlate with tuber induction. Tuber thickening proceeds via interfascicular cambium activity.

Practical Guidance

In this experimental system, GA reduced tuberization while ABA and short-day conditions promoted tuberous-root growth. The findings support the view that hormone balance, photoperiod, and cutting position all influence tuber formation in dahlias.

Why This Source Matters

This paper established two of the most practically consequential findings in dahlia tuberization research. First, that GA inhibits tuberization while ABA promotes it — a direct hormonal antagonism with implications for how growers think about anything that elevates or suppresses gibberellin activity in plants intended for tuber production. Second, that tuber thickening is associated with interfascicular cambial activity — an anatomical finding that connects the physiological trigger to a specific developmental process. The endogenous ABA-like inhibitor assay data also provide biochemical support for the short-day induction model that underlies the broader tuberization framework.

Publication Type

Conference Proceedings Paper

Full Citation

Halevy, A. H., & Biran, I. (1974). Hormonal regulation of tuberization in Dahlia. II International Symposium on Flower Bulbs, 47, 319–330.

Study System

Dahlia cv. 'Choot Hashani'; whole plants and single-node leaf-bud cuttings.

Experimental Context

Controlled short-day and long-day photoperiod conditions; exogenous hormone treatments in greenhouse experiments.

Experimental Design

Treatment of whole plants and cuttings with ABA, GA, ethrel, SADH, and B-Nine under defined photoperiods; measurement of fresh weights, tuber/top ratios, node position effects, and ethylene evolution.

Key Results

Short days promoted tuberization. Long days inhibited it. ABA promoted tuberization. GA inhibited tuberization and enhanced shoot growth. Ethrel promoted tuberization and increased ethylene. Basal nodes produced greater tuber mass.

Mechanistic Insight

ABA acts directly in tuber initiation. GA suppresses tuberization via promotion of vegetative growth and altered assimilate partitioning. Ethylene is associated with the early tuber initiation phase.

Practical Guidance

Short-day conditions and reduced vegetative growth favor tuber formation. ABA or ethylene-releasing treatments can enhance tuber initiation. Basal node cuttings may improve tuber yield.

Why This Source Matters

Read alongside KC-0702 (above), this paper completes the hormonal picture of dahlia tuberization from the same research group. Where KC-0702 establishes the GA–ABA antagonism with anatomical and biochemical detail, KC-0723 adds ethylene to the picture: ethrel treatments promoted tuberization and were associated with increased ethylene evolution, placing ethylene within the early induction phase. The node-position effect — greater tuber mass from basal nodes than from upper nodes — recurs here as well, with implications for cutting selection in propagation systems where tuber yield is a goal. Together, these two papers represent the most detailed mechanistic account of hormonal tuberization control available in the dahlia literature.

The Knowledge Card summaries in this collection were developed from the Dahlia Doctor research archive and checked against available source records during editorial preparation. AI tools assisted with retrieval, formatting, comparison, and assembly of the collection. All curatorial decisions — including source selection, topic organization, interpretation, and final editorial framing — were made by the author.