Dahlia Doctor Research Library: How Dahlias Form Roots and Tubers

A Curated Knowledge Card Collection

Copyright © 2026 by Steve K. Lloyd
All Rights Reserved

Dahlia growers usually talk about roots in two ways: the roots that form on cuttings during propagation, and the tubers that develop underground and carry the plant through winter. Botanically, those “tubers” are tuberous roots: enlarged adventitious roots that store energy. The research in this collection shows that these two root systems are more connected than they may appear.

The same developmental category links cutting roots and dahlia tubers. Both arise from stem, hypocotyl, crown, or basal cutting tissue rather than from a primary tap root. Both depend on tissue condition, cambial activity, vascular development, and assimilate supply to reach their functional form. The question of why some dahlia cuttings root easily while others fail, and why some adventitious roots become substantial tubers while others remain thin and fibrous, involves several of the same physiological variables: endogenous growth regulators, sink competition, bud state, tissue maturity, and the balance between above-ground growth and below-ground development.

This collection brings together eleven Knowledge Cards spanning dahlia root anatomy, adventitious root initiation, the developmental transition from root to tuberous root, and applied propagation treatments such as cutting type, auxin application, basal shading, and commercial rooting formulations. The anatomical work comes first because it establishes what a dahlia tuber actually is before the collection addresses how one forms, and how propagation decisions affect that outcome.

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-0878 also appears in the Dahlia Doctor Research Library collection on growth regulators in dahlia production. It is reproduced here in full because its IBA dose-response and cutting-type findings are directly relevant to this collection's argument about rooting physiology and root-system quality.

This collection uses grower language and botanical language together. Growers call the underground storage organs “tubers.” In the research literature, dahlia tubers are more precisely described as tuberous roots because they are enlarged adventitious roots, not true stem tubers.

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.

Experimental Context
Field-grown dahlia plants examined for the timing of adventitious root production, tuberous root enlargement, defoliation effects, shading effects, and photoperiod effects on root number and root diameter.

Experimental Design
Seedlings were planted in the field and dug at approximately ten-day intervals from June to November. Plants grown from tuberous roots were dug at repeated intervals during the growing season. 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 used an 8-hour photoperiod for 20 or 40 days. Long-day treatments used a continuous 24-hour photoperiod and were evaluated 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 after October. Seedling plants and plants grown from tuberous roots showed similar root-formation patterns. June and July defoliation 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 and increased root diameter. Long-day treatment showed no clear difference in root number or root diameter compared with natural daylength. Flower buds were absent under long-day treatment on August 25 but present by September 25.

Mechanistic Insight
Dahlia tuberous roots are enlarged adventitious roots arising from the stem or hypocotyl region. Seed roots did not enlarge. Adventitious roots and tuberous roots had similar anatomical structure and were distinct from normal fibrous roots. Under natural daylength, adventitious root number increased until above-ground growth slowed in early to mid-August, while root enlargement continued later in the season. Short-day conditions promoted enlargement of existing adventitious roots.

Practical Guidance
A developmental period before short-day conditions was described as necessary for obtaining adequate tuberous root number. Early leaf removal reduced adventitious root number. Later leaf removal and October shading reduced root thickening.

Why This Source Matters
This 1960 field study established several findings that remain foundational to understanding dahlia tuber biology. First, it confirmed that the roots that enlarge into tuberous roots are adventitious. They arise from stem or hypocotyl tissue, not from a primary tap root, and they are structurally distinct from normal fibrous roots. Second, it showed that root number and root enlargement are temporally separated processes governed by different conditions. Adventitious root production peaks during active vegetative growth in early summer, while root thickening intensifies later in the season under conditions that include naturally shortening days. Third, the defoliation and shading experiments demonstrated that leaf area matters for both processes, but at different developmental windows. That separation of root formation from root enlargement provides the conceptual foundation for KC-0005 and KC-0753, and it also explains why cutting propagation decisions that affect adventitious root initiation can connect to tuber quality later in the season.

Publication Type
Journal Article

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

Study System
Dahlia seedlings from a single-flowered strain, plants of 'Tensin' grown from storage roots, and cuttings from both propagation types.

Experimental Context
Anatomical and morphological investigation of primary roots and adventitious roots to determine which root types are capable of thickening into tuberous roots, and to identify the internal structures associated with thickening capacity.

Experimental Design
Root and tuber tissue were collected from seedlings, storage-root plants, and cuttings during the 1958 and 1959 growing seasons. The authors prepared hand sections and microtome sections, stained them with Delafields haematoxylin and safranin, and examined them microscopically. Root diameter was compared with internal structural variables including pith size, number of primary xylem strands, and number of rings of secondary vessels.

Key Results
Primary roots had a tetrarch protostele, small pith, and limited thickening capacity. They did not develop into tuberous roots, and lateral roots arising from primary roots showed the same general pattern. The first adventitious roots appeared at the base of the cotyledon when about four to eight leaves had opened on the stem. As plants developed, additional adventitious roots arose from the cotyledonary node and lower stem nodes, the region commonly called the crown. Adventitious roots in cuttings arose near the cut surface and adjacent nodes.

Adventitious roots differed anatomically from primary roots. They had polyarch vascular bundles, a relatively large pith, and the capacity to thicken through cambial activity and secondary xylem formation. Thickening was associated with the number of rings of secondary vessels and with pith development, but not with the number of primary xylem strands present when the adventitious root first formed.

Mechanistic Insight
Tuberous root thickening is governed primarily by sustained cambial activity, secondary xylem development, and pith enlargement. Primary roots lack the anatomical foundation for substantial thickening. Adventitious roots, by contrast, possess the vascular and pith structure needed to become tuberous roots, although not every adventitious root ultimately thickens. Roots that arise late or under unfavorable conditions may remain fibrous.

Practical Guidance
For tuber production, the important issue is not root number alone. Conditions must also support the continued activity of adventitious root tissues after they form. In cutting propagation, root initiation occurs near the cut surface and adjacent nodes, making basal tissue condition and node placement directly relevant to later root-system development.

Why This Source Matters
This paper supplies the anatomical evidence behind a point growers often experience but rarely see directly: dahlia tubers are not enlarged tap roots. They are enlarged adventitious roots. The study explains why primary roots remain thin while adventitious roots can become tuberous. Primary roots have little pith and limited thickening capacity; adventitious roots have larger pith, polyarch vascular structure, and active cambial tissues capable of producing the secondary growth needed for enlargement.

The paper also links seed-grown plants, tuber-grown plants, and cuttings into one developmental framework. In all three cases, the roots that matter for future tuber formation arise from crown, stem, hypocotyl, or basal cutting tissues rather than from the original primary root. That finding makes this source central to the whole collection. It connects the field timing of KC-0004, the dry matter timeline of KC-0753, and the cutting-base studies in KC-0699, KC-0105, and KC-0878.

Publication Type
Peer-reviewed Journal Article

Full Citation
Mejía Muñoz, J. M., & Mendoza Arizmendi, J. L. (1995). Distribución de materia seca y desarrollo de raíces tuberosas en plantas de dalia (Dahlia variabilis Cav.) [Distribution of dry matter and tuberous root development in dahlia plantlets (Dahlia variabilis Cav.)]. Revista Chapingo Serie Horticultura, 3, 135-138.

Study System
Seed-grown dahlia plantlets (Dahlia variabilis Cav.).

Experimental Context
Dry matter distribution and tuberous root development tracked from germination to first floral bud under greenhouse conditions.

Experimental Design
Weekly destructive sampling of 10 plants from 200 seedlings across 84 days. Measurements included dry weights for stems, leaves, and roots, along with tuber number, crown diameter, and developmental stage.

Key Results
Tuber initiation occurred around 14 days at the cotyledonary node. Maximum tuber number occurred around 63 days. Dry matter shifted from shoots to tuberous roots after stem dry weight peaked. Floral bud appeared at 84 days.

Mechanistic Insight
Tuber initiation is linked to the cotyledonary axils and crown enlargement, with assimilate partitioning shifting from vegetative growth toward storage roots after the shoot biomass peak.

Practical Guidance
Supports attention to early nutrition, light, and growth conditions before floral initiation when interpreting storage root development in seed-grown dahlias.

Why This Source Matters
This study traced the developmental sequence of tuberous root initiation and assimilate redistribution in seed-grown dahlias from germination through 84 days. It provides a timeline that connects the anatomical findings of KC-0004 and KC-0005 to measurable changes in dry matter allocation.

The finding that tuber initiation begins as early as 14 days at the cotyledonary node places tuber development early in the plant's life rather than solely at the end of the season. The shift in dry matter from shoots to tuberous roots after the shoot biomass peak shows that storage root development competes with vegetative growth for assimilates. For growers, that means early growing conditions can influence what eventually gets dug in fall. Together with KC-0004 and KC-0005, this card completes the first cluster's account of what a dahlia tuber is, when it begins to form, and what drives its growth.

Publication Type
Peer-reviewed Journal Article

Full Citation
Biran, I., & Halevy, A. H. (1973c). Endogenous levels of growth regulators and their relationship to the rooting of dahlia cuttings. Physiologia Plantarum, 28(3), 436-442.

Study System
Dahlia variabilis cultivars 'Choot Hashani', 'Orpheo', 'Lavender Perfection', and 'Hermiona'.

Experimental Context
Comparison of easy- and difficult-to-root cuttings differing by cultivar, maturity, and bud type under controlled photoperiod conditions.

Experimental Design
Quantification of diffusible and extractable auxins, cofactors, and inhibitors via chromatography and multiple bioassays. Analysis included exudates from decapitated plants, reciprocal grafting, ABA treatments, and IBA treatments.

Key Results
No correlation was found between auxin or cofactor levels and rooting ability. Higher inhibitor activity was present in difficult-to-root and reproductive cuttings. An inhibitor was present in root exudates of mature plants. Grafting onto a difficult-to-root rootstock reduced scion rooting. ABA synergized with IBA but was not identified as the primary inhibitor.

Mechanistic Insight
Rooting inhibition is associated with inhibitors originating in the root system and translocated upward, accumulating in reproductive or mature shoots. Auxin levels are not the limiting factor in dahlia rooting difficulty.

Practical Guidance
Rooting differences among cultivars and shoot types reflect endogenous inhibitor levels and rootstock effects rather than simple auxin deficiency.

Why This Source Matters
This paper challenged the intuitive assumption that easy-to-root cuttings root well because they have more auxin. The experimental data did not support that. Instead, the evidence pointed to inhibitors, not auxin deficiency, as the driver of rooting difficulty in dahlias. Those inhibitors appeared to originate in the root system and move upward into reproductive or mature shoots.

The grafting experiment was especially important. Placing a scion from an easy-to-root cultivar onto a difficult-to-root rootstock reduced scion rooting, supporting the translocation hypothesis directly. For growers and propagators, the implication is that adding auxin may not solve a rooting problem that originates in inhibitor accumulation rather than auxin shortage. This finding also frames the bud-state and shading data in KC-0700 and KC-0699. Those treatments work not simply by adding auxin, but by altering tissue state and the internal conditions that influence rooting competence.

Publication Type
Peer-reviewed Journal Article

Full Citation
Biran, I., & Halevy, A. H. (1973b). The relationship between rooting of dahlia cuttings and the presence and type of bud. Physiologia Plantarum, 28(2), 244-247.

Study System
Dahlia cultivars 'Orpheo', 'Lavender Perfection', and 'Choot Hashani'.

Experimental Context
Propagation of stem cuttings differing in bud presence, bud type, and growth state under controlled photoperiod. Rooting took place under intermittent mist in vermiculite.

Experimental Design
Comparison of five cutting types with and without bud removal. Measurements included rooting percentage, node position effects, and response to IBA and BA treatments.

Key Results
Cuttings with non-growing buds rooted better than those with actively growing buds. Reproductive buds suppressed rooting. Bud removal increased rooting. An inverse relationship was found between bud growth rate and rooting. Lower nodes rooted better. IBA combined with BA improved rooting and reduced bud growth.

Mechanistic Insight
Growing buds act as metabolic sinks that inhibit rooting, while quiescent buds may support rooting through hormonal balance and cambial activation. The competitive relationship between bud development and root initiation appears to be mediated through sink strength and growth-regulator balance.

Practical Guidance
Use non-growing or disbudded cuttings; remove reproductive buds; remove actively growing terminal portions; favor lower-node cuttings; consider combining auxin and cytokinin where appropriate to improve rooting and control bud growth.

Why This Source Matters
This paper introduced a practical and physiological framework for thinking about bud state as a rooting variable in dahlia cuttings. A grower might assume that a vigorously growing cutting would also root vigorously, but the data showed the opposite. Actively growing buds suppressed rooting, while removing them or choosing cuttings with quiescent buds improved outcomes.

The node-position effect adds another layer: lower-node cuttings rooted better than upper-node cuttings, consistent with the inhibitor translocation model developed in KC-0701. Taken together, KC-0700 and KC-0701 form a paired argument about what drives rooting difficulty in dahlias. One focuses on bud state and sink competition; the other focuses on endogenous inhibitors that underlie those differences.

Publication Type
Peer-reviewed Journal Article

Full Citation
Biran, I., & Halevy, A. H. (1973a). Stock plant shading and rooting of dahlia cuttings. Scientia Horticulturae, 1(2), 125-131.

Study System
Dahlia variabilis cultivars 'Choot Hashani', 'Orpheo', and 'Lavender Perfection'; stock plants and terminal cuttings.

Experimental Context
Long-day grown stock plants subjected to continuous, midday-only, or localized shading. Rooting was assessed under mist following IBA treatment.

Experimental Design
Whole-plant shading at approximately 50%; adjustable Saran frames providing 50-72% light reduction; basal-region etiolation treatments; light-intensity measurements at the shoot base; rooting percentage and root number recorded.

Key Results
Continuous shading increased rooting in 'Orpheo' but reduced cutting yield. Midday-only shading was ineffective in dense canopies. Localized basal shading markedly increased rooting percentage and root number. No improvement was found in the woody cultivar 'Lavender Perfection'.

Mechanistic Insight
Rooting enhancement is localized to the basal root-initiation zone. Shading promotes herbaceous tissue state and reduces sclerification. Response depends on the anatomical plasticity of the cultivar.

Practical Guidance
Localized shading of the future cutting base can improve rooting without the yield losses associated with whole-plant shading. Effectiveness depends on cultivar tissue response; woody cuttings may not benefit.

Why This Source Matters
This paper established that shading improves rooting not by changing the whole plant's light environment, but by acting specifically on the basal zone where roots will initiate. Localized shading of the shoot base reduced sclerification and maintained herbaceous tissue in that zone, making it a more competent rooting site.

The failure of the treatment to improve rooting in 'Lavender Perfection', the woodiest of the three cultivars tested, is as informative as the positive results. It indicates that the benefit depends on whether the basal tissue retains enough anatomical plasticity to respond. Read alongside KC-0701 and KC-0700, this paper completes the second cluster's argument by showing that rooting competence is a property of specific tissue zones rather than a whole-plant trait. The conditions at the cutting base, including tissue state, sclerification, and light history, are proximate determinants of whether adventitious roots initiate.

Publication Type
Journal Article

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

Study System
Dahlia pinnata.

Experimental Context
Vegetative propagation via stem cuttings; greenhouse comparison of heel versus non-heel cutting methods with standardized substrate and environment.

Experimental Design
Greenhouse comparison of heel versus non-heel cutting methods with standardized substrate and environment.

Key Results
Heel cuttings showed higher rooting percentage, greater root mass, and better early shoot development than non-heel cuttings.

Mechanistic Insight
Basal stem tissue in heel cuttings provides greater meristematic capacity and carbohydrate reserves, enhancing adventitious rooting.

Practical Guidance
Use heel cuttings to maximize rooting success and uniformity in dahlia propagation.

Why This Source Matters
This study provides direct experimental evidence that heel cuttings outperform non-heel cuttings in dahlia. It also offers a mechanistic rationale: the basal stem tissue retained in a heel cutting carries greater meristematic capacity and carbohydrate reserves than the cut surface of a non-heel cutting.

That rationale connects directly to the anatomical findings of KC-0005, where the structural features of the root-initiation zone determine rooting capacity. It also aligns with the localized basal-zone effects documented in KC-0699. The same region that benefits from shading is the region that a heel cutting preserves. Practically, this is one of the most actionable papers in the collection because the treatment is simple and the outcome difference is substantial.

Publication Type
Experimental Research Article

Full Citation
Hetman, J., & Pudelska, K. (2006). Ukorzenianie różnych typów sadzonek zielnych kilku odmian dalii zmiennej (Dahlia pinnata Cav.) [Rooting of different types of softwood cuttings of a few dahlia cultivars (Dahlia pinnata Cav.)]. Zeszyty Problemowe Postępów Nauk Rolniczych, 510, 195-202.

Study System
Eight cultivars of Dahlia pinnata Cav.: Aida, Ewelina, Krynica, Maja, My Love, Topmix Purple, Topmix Red, and Topmix White.

Experimental Context
Tubers placed in greenhouse boxes in early March; softwood cuttings collected from new shoots in mid-March. Study compared cutting type as a factor in rooting percentage, root-system fresh mass, root length, and above-ground fresh mass.

Experimental Design
Six cutting types were tested: top cuttings with two pairs of leaves and a piece of tuber; top cuttings with two pairs of leaves without a piece of tuber; top cuttings with two to three pairs of leaves from shoots having at least five to six pairs of leaves; middle-stem two-node cuttings; top cuttings from lateral shoots after earlier removal of the shoot tip; and top cuttings with at least five pairs of leaves. Cuttings were rooted in high peat and river sand in a 1:1 mixture at pH 5.8-6.0, treated with 0.2% NAA rooting powder, kept under foil tunnel cover, and evaluated after five to six weeks. The experiment was repeated in three seasons with forty-eight treatment combinations and ten cuttings per combination.

Key Results
The highest average rooting percentage was obtained from top cuttings taken from lateral shoots. Other cutting types also rooted well, with average rooting percentages ranging from 73% to 81%. Some cultivars showed rooting averages of 83% to 88%, while one cultivar showed a lower average of 58%. Cutting type significantly affected fresh root mass, root length, and fresh above-ground mass. Cuttings with a piece of tuber, cuttings without a piece of tuber, middle-stem two-node cuttings, and top cuttings from lateral shoots all produced well-developed root systems.

Mechanistic Insight
The presence or absence of a tuber piece and the position of the cutting on the shoot were associated with differences in root-system development and fresh mass. Cutting type influenced rooting quality more than rooting occurrence alone.

Practical Guidance
Several softwood cutting types can be used for propagation. Well-rooted cuttings were obtained from top cuttings with a piece of tuber, top cuttings without a piece of tuber, middle-stem two-node cuttings, and top cuttings from lateral shoots.

Why This Source Matters
This study extended the cutting-type question beyond the heel-versus-non-heel comparison of KC-0105 to a broader evaluation of six cutting types across eight cultivars over three seasons. The most useful finding is that cutting type affects root-system quality, including root mass, root length, and above-ground mass, more than it affects whether rooting occurs at all.

That distinction matters for production. If the goal is vigorous, transplantable plants rather than merely rooted cuttings, cutting-type choice has consequences that a simple rooting-percentage metric would understate. The cultivar range also reinforces a pattern seen throughout this collection: cultivar is a consistent source of variation in dahlia rooting outcomes, regardless of which treatment or management variable is being tested.

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 completely randomized design 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 proceeds via carbohydrate translocation and root primordia induction.

Practical Guidance
Under the tested mist-chamber conditions, IBA at 500-1000 ppm supported robust rooting, while a combined IBA and NAA treatment 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 runs throughout this collection.

Read alongside KC-0878, this study helps establish that both auxin dose and auxin combination influence rooting outcome in dahlia cuttings. It also shows that optimizing for different endpoints, such as rooting percentage, root length, or speed of rooting, may require different treatment choices.

Publication Type
Experimental Research Article

Full Citation
Singh, S., Singh, I., Miller, C. T., Dhatta, 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 x 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 were 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 here to directly compare heel cuttings against non-heel cuttings alongside an IBA dose-response series. That design makes it a bridge between the cutting-type findings of KC-0105 and KC-0919 and the auxin-response findings of KC-0199. Cutting type and auxin dose are both active variables, and this study tests them together.

The finding that callus formation may delay rather than facilitate rooting challenges a common assumption and has direct implications for cutting preparation and timing. The identification of a usable dose 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. The observation of short tuberous roots in heel cuttings also connects this applied propagation study back to the root anatomy and developmental physiology in the first cluster.

Publication Type
Research Report

Full Citation
van Zuilichem, J. A. A., & Stevens, L. H. (2003). Beworteling stekken dahlia (2002-2003) [Rooting of dahlia cuttings (2002-2003)]. Praktijkonderzoek Plant & Omgeving.

Study System
Dahlia cuttings.

Experimental Context
Field and greenhouse propagation trials in an organic production context; comparative evaluation of synthetic auxin versus biological and carrier-based rooting alternatives.

Experimental Design
Comparative trials of synthetic auxin versus biological and carrier-based rooting alternatives.

Key Results
Rhizopon B 0.2% produced superior rooting and fleshy root systems compared with alternatives. Biological alternatives showed limited, cultivar-dependent effects.

Mechanistic Insight
Synthetic auxin provides a more consistent and effective rooting stimulus than bacterially produced auxin under the tested conditions.

Practical Guidance
Use conventional auxin rooting powders for dependable propagation; biological alternatives offer limited benefit under the tested conditions.

Why This Source Matters
This Dutch horticultural research report evaluated whether biological or carrier-based rooting alternatives could substitute for conventional synthetic auxin in dahlia cutting propagation. Under the conditions tested, they could not. The clear performance advantage of Rhizopon B 0.2% over the alternatives, combined with cultivar-dependent variation in response to biological products, adds a practical grounding note to the auxin cluster.

The physiological mechanisms documented in KC-0199 and KC-0878 depend on effective delivery of an appropriate auxin dose, and not all rooting products deliver that equally. The organic production context also gives this report specific relevance for growers operating under restrictions on synthetic inputs, where the finding that biological alternatives showed limited benefit is directly applicable to production decisions.

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.