Dahlia Doctor Research Library: Dahlia Nutrient Management and Soil Fertility

A Curated Knowledge Card Collection

Copyright © 2026 by Steve K. Lloyd
All Rights Reserved

Dahlias are hungry plants, but nutrient management is not simply a matter of giving them more fertilizer. The research record is more interesting than that. Nitrogen affects growth and flower yield, but too much or too little can change plant balance. Phosphorus and potassium influence productivity, quality, and tuber development. Organic manures, vermicompost, biofertilizers, and integrated nutrient systems can improve growth and yield in some studies, but their effects depend on the cultivar, soil, production system, and treatment combination. Even nutrient deficiencies have been studied directly in dahlias, giving growers a clearer picture of what mineral stress can look like before it becomes a crop failure.

For gardeners and cut-flower growers, this matters because dahlias have to do several things at once. They must build a strong plant, produce flowers over a long season, maintain stem and bloom quality, and still store enough energy below ground to form usable tubers. Fertility decisions affect all of those outcomes. A program that pushes lush top growth is not automatically the same as one that improves flower yield, tuber yield, or storage quality.

This Research Library collection brings together Dahlia Doctor Knowledge Cards on nitrogen management, nutrient deficiencies, phosphorus and potassium treatments, integrated nutrient management, organic amendments, biofertilizers, and foliar fertilization. Together, these studies show that dahlia fertility is best understood as a balancing act: mineral nutrients, organic inputs, microbial inoculants, soil conditions, application timing, and cultivar response all shape the final result.

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 studies in the integrated nutrient management cluster address both flower yield and tuber yield within the same experiment; tuber-related findings are noted within their Key Results fields rather than duplicated across clusters.

Publication Type

Conference Proceedings Paper

Full Citation

Barnes, J., Whipker, B., McCall, I., & Frantz, J. (2015). Characterization of nutrient disorders of Dahlia × hybrida 'Maxi Morelia'. Acta Horticulturae, 1062, 39–48.

Study System

Dahlia × hybrida 'Maxi Morelia' grown in greenhouse silica-sand culture.

Experimental Context

Controlled soilless production system using single-element nutrient omission and boron toxicity treatments to characterize deficiency and toxicity symptoms and establish critical tissue concentrations.

Experimental Design

Single-element omission treatments plus boron toxicity, using a modified Hoagland's solution with weekly solution replacement. Photographic symptom documentation was conducted alongside foliar tissue analysis by CHN and ICP-OES methods. Critical tissue concentrations were established at first symptom appearance.

Key Results

Element-specific deficiency symptomology was documented for each omitted nutrient. Significant dry mass reductions were recorded for several nutrient omissions. Critical tissue concentrations were established at first symptom appearance for each element. Copper and molybdenum deficiencies were asymptomatic despite reduced tissue levels. Boron toxicity produced characteristic marginal necrosis.

Mechanistic Insight

Symptom expression reflects nutrient mobility and physiological role within the plant. Sap responses distinguish mobile from immobile nutrient deficiencies. The asymptomatic response to copper and molybdenum deficiency indicates that tissue testing is necessary to detect those deficiencies reliably, because visual monitoring alone is insufficient.

Practical Guidance

This study provides visual diagnostic standards and critical tissue concentration benchmarks for greenhouse dahlia nutrient management. Growers managing container or soilless production systems can use the documented symptom progression and tissue thresholds to identify deficiencies before they produce significant yield loss.

Why This Source Matters

This is the only source in this collection — and one of very few in the dahlia literature — to systematically document nutrient deficiency and toxicity symptoms under controlled conditions with element-by-element omission and quantified tissue analysis. Every other study in this collection evaluates how much to apply and what yields result. This one establishes what goes wrong when nutrients are absent or excessive, and what those problems look like in the plant. The critical tissue concentrations it established give growers and diagnosticians a reference standard for interpreting foliar test results in dahlia, and the photographic symptom documentation provides a visual diagnostic tool that is not available elsewhere for this crop.

Publication Type

Journal Article

Full Citation

Oliver, F., Stock, M., & Nischwitz, C. (2024). Nitrogen management and virus incidence on cut flower production of dahlia. Journal of Environmental Horticulture, 42(1), 14–22.

Study System

Dahlia pinnata 'Café au Lait' grown under field conditions in a three-year trial with grower-participant comparison.

Experimental Context

Field trial evaluating nitrogen rate effects on cut-flower yield and quality, with concurrent assessment of virus incidence and its interaction with nitrogen management.

Experimental Design

Randomized complete block design with five nitrogen rates from 0 to 224 kg N per hectare. Grower-participant comparison was included alongside the replicated trial.

Key Results

Maximum cut-flower yields were achieved at 168 to 224 kg N per hectare. Virus-free stock eliminated yield culling caused by virus-infected plants. Nitrogen rate interacted with plant health status in determining final yield outcomes.

Mechanistic Insight

Nitrogen enhanced vegetative growth and tuberization at rates up to the identified optimum. Virus infection suppressed yield independently of nitrogen rate, with infected plants producing culled or unmarketable stems regardless of fertility inputs.

Practical Guidance

The study supports using approximately 168 kg N per hectare as a working nitrogen rate for cut dahlia production, in combination with certified virus-free stock and soil-test-based fertility management. The interaction between nitrogen rate and virus status means that nitrogen optimization alone will not achieve expected yield gains if propagation material carries latent virus.

Why This Source Matters

This is the most recent nitrogen management study in this collection and the only one conducted as a multi-year field trial in a North American cut-flower production context. Its most practically important finding is not simply that dahlia responds to nitrogen, but that the combination of appropriate nitrogen rate and virus-free propagation material is what determines actual yield outcomes. Growers who optimize fertility without addressing stock health will still incur yield losses that no fertilizer program can correct. That interaction — fertility management and disease management as inseparable components of a production system — is the central contribution of this source.

Publication Type

Experimental Research Article

Full Citation

Khan, G. A., Sajid, M., Zubair, M., & Noor-ul-Amin. (2007). Response of Dahlia pinnata to different levels of nitrogen alone and in combination with constant doses of phosphorus and potassium. Sarhad Journal of Agriculture, 23(3), 571–576.

Study System

Dahlia pinnata grown under field conditions in clay loam soil with low baseline nitrogen, phosphorus, and potassium at Peshawar, Pakistan.

Experimental Context

Field trial testing nitrogen applied alone and in combination with constant doses of phosphorus and potassium, to evaluate the effect of nutrient balance on flowering, vegetative growth, root development, and plant architecture.

Experimental Design

Seeds were sown in a nursery seedbed and seedlings transplanted to field subplots. Twenty fertilizer treatments were arranged in a randomized complete block design with three replications. Nitrogen was applied at 0, 15, 20, 25, and 30 g per square foot, either alone or with constant phosphorus at 15 g per square foot, constant potassium at 15 g per square foot, or both phosphorus and potassium at 15 g per square foot each. Phosphorus and potassium were applied before planting. Nitrogen was split between planting and one month after transplanting. Parameters measured included days to flowering, flowers per plant, plant height, leaves per plant, primary root length, leaf area, and root-to-stem ratio.

Key Results

Fertilizer treatments significantly affected days to flowering, flowers per plant, leaves per plant, primary root length, leaf area, and root-to-stem ratio. Plant height was not significantly affected. Nitrogen applied alone at 30 g per square foot produced the latest flowering. Nitrogen alone at 25 g per square foot produced the highest plant height, leaves per plant, and leaf area. The combination of 25 g nitrogen, 15 g phosphorus, and 15 g potassium per square foot produced the highest flowers per plant and primary root length. The lowest flowers per plant and root-to-stem ratio were recorded with nitrogen alone at 30 g per square foot.

Mechanistic Insight

Nitrogen applied alone encouraged vegetative growth and delayed flowering, particularly at the highest rate. Phosphorus was associated with root proliferation and potassium functioned as a growth regulator in this system. The combined NPK treatment improved overall plant performance across multiple measured traits, indicating that nutrient balance rather than nitrogen rate alone determines flowering and root outcomes.

Practical Guidance

Under the agro-climatic conditions of Peshawar, the source reported best overall performance from the treatment combining 25 g nitrogen, 15 g phosphorus, and 15 g potassium per square foot. The practical takeaway is not that this rate should be transferred directly to other soils or climates, but that high nitrogen applied without balancing phosphorus and potassium can delay flowering and reduce flower number even when it increases vegetative growth. For growers, the study is most useful as a caution against nitrogen-heavy fertility programs that are not guided by soil testing and overall nutrient balance. 

Why This Source Matters

This study isolates the effect of nutrient balance in a way that most INM trials do not. By applying nitrogen alone at multiple rates and then adding phosphorus and potassium as constants, it shows that the nitrogen-only effect on flowering is negative at high rates — more nitrogen without balancing phosphorus and potassium delays bloom and reduces flower number even when it increases leaf area and height. That finding gives the nitrogen discussion in this collection a practical boundary condition: nitrogen is essential, but unbalanced nitrogen application is not simply neutral. In this study, high nitrogen without balancing phosphorus and potassium shifted the plant away from flowering and toward vegetative growth. 

Publication Type

Experimental Research Article

Full Citation

El-Alsayed, S. G., Ismail, S., & Eissa, D. (2018). Impact of seaweed extract and phosphorus application on productivity of dahlia plants. Assiut Journal of Agricultural Sciences, 49(1), 159–188.

Study System

Dahlia pinnata plants grown from divided tuberous-root clumps in sandy soil.

Experimental Context

Two pot experiments conducted across two successive seasons in sandy soil, evaluating seaweed extract and phosphorus treatments for effects on vegetative growth, flowering traits, tuberous-root production, leaf chemical composition, and sandy-soil phosphorus behavior.

Experimental Design

Factorial randomized block design with four seaweed extract concentrations and four phosphorus levels across two seasons. Seaweed extract was applied as a soil drench. Phosphorus was applied as triple superphosphate. Measurements included stem length, stem dry weight, leaf number, leaf dry weight, leaf area, days to flowering, flower diameter, flowering duration, flower dry weight, tuberous-root number, tuberous-root fresh weight, leaf chlorophyll, leaf carbohydrates, leaf nitrogen, leaf phosphorus, leaf potassium, soil chemical properties, soil surface charge, and phosphate adsorption.

Key Results

Seaweed extract at 1% and phosphorus at 200 ppm produced the highest or among the highest values for most vegetative, flowering, tuberous-root, and leaf chemical measurements. The combination of 1% seaweed extract with 200 ppm phosphorus produced the greatest stem length and increased tuberous-root fresh weight in the reported interaction results. Higher rates did not consistently improve growth or yield. Seaweed-treated soil had greater negative surface charge than triple-superphosphate-treated soil. Phosphate adsorption was lower in seaweed-treated soil than in triple-superphosphate-treated soil.

Mechanistic Insight

The source attributes plant responses to nutrient supply, growth-regulator content of the seaweed extract, improved vegetative growth, increased photosynthetic surface area, increased carbohydrate accumulation, and phosphorus roles in photosynthesis, respiration, enzyme activation, sugar translocation, and osmotic regulation. Seaweed extract increased net negative soil surface charge and reduced phosphate adsorption capacity in sandy soil, improving phosphorus availability at the soil level.

Practical Guidance

The source recommends growing dahlia in sandy soil with seaweed extract at 1% and phosphorus at 200 ppm. The soil chemistry findings suggest an additional rationale for seaweed extract beyond direct nutrient supply: improved phosphorus availability through reduced adsorption to soil particles, which is a practical consideration in sandy or low-organic-matter soils where phosphorus fixation limits availability.

Why This Source Matters

This study introduces seaweed extract as a component of dahlia phosphorus management and shows that its effect operates partly at the soil level rather than only through direct nutrient supply to the plant. The reduction in phosphate adsorption in seaweed-treated sandy soil is a mechanistically distinct finding from the yield and growth data, and it gives growers working in sandy or low-fertility soils a practical reason to consider seaweed extract as a soil amendment rather than simply a foliar stimulant. The combination of plant-response data and soil chemistry data in the same experiment makes this a more complete phosphorus management study than most in this collection.

Publication Type

Journal Article

Full Citation

Hamayl, A. F., El-Saka, M. M., El-Boraie, E. A. H., & Gad, A. E. A. (2016). Effect of potassium sulfate and calcium borate on improving quality and production of Dahlia flowers. Journal of Plant Production, 7(12), 1281–1286.

Study System

Dahlia pinnata grown under field conditions.

Experimental Context

Field experiment evaluating potassium sulfate soil applications and calcium borate foliar sprays, alone and in combination, over two seasons.

Experimental Design

Randomized complete block design with potassium sulfate soil applications at 10 or 20 g per plant and calcium borate foliar sprays at reported concentrations, applied alone and in combination over two seasons.

Key Results

Combined potassium sulfate at 20 g per plant plus the higher calcium borate foliar treatment maximized vegetative growth, flower number and size, stem strength, vase life, tuber number, and tuber diameter across both seasons.

Mechanistic Insight

Potassium is associated with carbohydrate synthesis, osmotic regulation, and overall plant growth. Calcium and boron are associated with cell-wall integrity, lignification, stem strength, and nutrient transport. The combination of soil-applied potassium and foliar calcium borate addresses both structural and metabolic aspects of dahlia growth and flower quality simultaneously.

Practical Guidance

In this field experiment, combined potassium sulfate at 20 g per plant with calcium borate foliar application improved flower number and size, stem strength, vase life, tuber number, and tuber diameter relative to single-nutrient treatments and untreated controls. Direct use should be guided by soil testing for potassium status and by boron-safety limits, as boron has a narrow window between deficiency and phytotoxicity.

Why This Source Matters

This study is the only source in this collection to specifically evaluate calcium and boron alongside potassium in a dahlia fertility context. Stem strength and vase life are cut-flower quality traits that most fertility studies in this collection do not measure directly, and the finding that the potassium-calcium-boron combination improved both of those traits alongside tuber number and diameter makes this study particularly useful for cut-flower producers. It also reinforces the collection's broader theme that different nutrients influence different outcome dimensions — and that a program targeting flower yield is not automatically the same as one that maximizes cut-flower quality or tuber development.

Publication Type

Experimental Research Article

Full Citation

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

Study System

Dahlia variabilis cv. SP Kamala grown under field conditions in sandy loam soil at pH 7.2 under Allahabad agro-climatic conditions, Uttar Pradesh, India.

Experimental Context

Field experiment conducted from November 2012 to March 2013, evaluating combinations of organic manures and biofertilizer inoculants for effects on plant growth, flower yield, tuber production, and benefit-cost ratio.

Experimental Design

Randomized block design with ten treatments and three replications. Twenty-five-day-old seedlings with three to five leaves were transplanted at 60 × 60 cm spacing with nine seedlings per plot. Treatments included a control with recommended NPK, farmyard manure, vermicompost, Azotobacter, Azospirillum, and phosphorus-solubilizing bacteria in different combinations. Analysis of variance with critical difference at the 5% significance level.

Key Results

The treatment combining vermicompost at 2.5 t per hectare, Azotobacter at 2.0 kg per hectare, and phosphorus-solubilizing bacteria at 2.0 kg per hectare produced the highest plant height, number of primary branches, number of flowers per plant, flower yield per plant, flower yield per hectare, weight of tuber, number of tubers per plant, tuber yield per plant, tuber yield per hectare, and benefit-cost ratio. The treatment combining farmyard manure, Azospirillum, and phosphorus-solubilizing bacteria produced the highest flower size. The control produced the lowest values for several flowering and tuber-production measurements.

Mechanistic Insight

The source attributes observed treatment effects to combined action of organic manures and microbial inoculants: biofertilizers enrich soil nutrient quality through microorganism activity, while organic manure supplies substrate for microbial communities and improves soil porosity and nutrient availability.

Practical Guidance

The treatment combining vermicompost at 2.5 t per hectare with Azotobacter and phosphorus-solubilizing bacteria at 2.0 kg per hectare each was concluded to be superior for plant growth, flower yield, tuber yield, and benefit-cost ratio under the tested cultivar and location. Results should be interpreted within the agro-climatic and soil context of the trial before direct application elsewhere.

Why This Source Matters

This study is notable for including benefit-cost ratio as a measured outcome alongside agronomic parameters, which anchors the biofertilizer discussion in economic as well as biological terms. The finding that the top-performing treatment used vermicompost and microbial inoculants rather than higher rates of synthetic fertilizer, and that it outperformed the recommended NPK control across nearly all measured traits, gives the organic and biofertilizer approach a practical argument beyond environmental preference. It also documents a case where the combination of microbial inoculants — nitrogen-fixing Azotobacter plus phosphorus-solubilizing bacteria — outperformed treatments using individual inoculants alone.

Publication Type

Experimental Research Article

Full Citation

Raghunandan, T., Collis, J. P., Saravanan, S., & Barman, K. S. (2021). Effect of integrated nutrient management on plant growth and tuber yield of Dahlia (Dahlia variabilis) cv. Kenya White. International Journal of Plant & Soil Science, 33(24), 80–84.

Study System

Dahlia variabilis cv. Kenya White grown under field conditions under Allahabad agro-climatic conditions, India.

Experimental Context

Spring growing season trial evaluating integrated nutrient management treatments combining inorganic fertilizers, organic manures, and biofertilizer inoculants for effects on plant growth and tuber yield.

Experimental Design

Thirteen fertilizer, organic manure, and biofertilizer treatment combinations tested in a randomized complete block design with three replications. Treatments included recommended NPK fertilizer dose alone and reduced recommended fertilizer doses combined with Azotobacter, farmyard manure, vermicompost, or combined organic and biofertilizer inputs. Forty-day-old seedlings were transplanted at 45 × 60 cm spacing.

Key Results

The treatment combining 75% recommended fertilizer dose with Azotobacter at 2.5 kg per hectare, farmyard manure at 10 t per hectare, and vermicompost at 10 t per hectare recorded the highest plant height, plant spread, number of branches per plant, number of leaves per plant, tuber weight, number of tubers per plant, and tuber yield per plant. The control treatment recorded the lowest growth parameters across all measured traits.

Mechanistic Insight

The source attributes increased growth and tuber yield to combined nutrient supply from inorganic fertilizer, organic manure, vermicompost, and Azotobacter. The proposed mechanisms include improved nutrient availability, atmospheric nitrogen fixation, phosphorus solubilization, growth-promoter production, photosynthetic activity, carbohydrate synthesis, root formation, and transfer of assimilates into tuber development.

Practical Guidance

A treatment combining 75% of the recommended fertilizer dose with Azotobacter, farmyard manure, and vermicompost produced the highest measured growth and tuber yield parameters in this trial. The result indicates that a reduced synthetic fertilizer input, supplemented with organic and microbial inputs, can outperform full recommended NPK alone for tuber yield — a finding with practical relevance for growers looking to reduce synthetic inputs without sacrificing tuber production.

Why This Source Matters

This study is useful in this collection because it directly tests whether a reduced synthetic fertilizer rate combined with organic and microbial inputs can match or exceed the full recommended NPK dose for tuber yield outcomes. The answer in this trial was yes, and across multiple growth parameters simultaneously. Read alongside KC-0017, which reaches a similar conclusion for a different cultivar and treatment combination, the two studies together suggest that integrated approaches to nutrient management are not simply a philosophical preference but a production strategy with documented tuber yield support in dahlia-specific field trials.

Publication Type

Journal Article

Full Citation

Kumar, N., Prasad, V., & Pal Yadav, N. (2019). Effect of chemical fertilizers and bio fertilizers on flower yield, tuberous root yield and quality parameter on dahlia (Dahlia variabilis L.) cv. Kenya Orange. Journal of Pharmacognosy and Phytochemistry, 8(4), 2265–2267.

Study System

Dahlia variabilis cv. Kenya Orange grown under field conditions.

Experimental Context

Field trial evaluating NPK fertilizer and biofertilizer combinations for effects on flower yield, tuberous root yield, and quality parameters.

Experimental Design

Randomized block design with 13 fertilizer treatments incorporating Azotobacter or phosphorus-solubilizing bacteria in various combinations with NPK inputs, with three replications.

Key Results

Treatment T3 maximized flower yield and vase life. Treatment T10 maximized tuber number, tuber size, and tuber yield. The treatments producing the best flower yield and the best tuber yield were not the same treatment.

Mechanistic Insight

Nutrient balance and biofertilizer-mediated nitrogen and phosphorus availability alter biomass allocation between flowering and tuber formation. The divergence between the flower-yield-optimizing and tuber-yield-optimizing treatments indicates that the plant responds to fertility inputs by shifting allocation priorities, and that a single treatment cannot simultaneously maximize both outputs.

Practical Guidance

Integrated fertilizer management can be adjusted toward either flower production or tuber yield depending on production goals. The key finding — that the treatments maximizing flower yield and tuber yield differed — means that growers should clarify their primary production goal before selecting a fertility program, rather than assuming that higher overall fertility will improve both outcomes simultaneously.

Why This Source Matters

This study documents a direct trade-off between flower yield and tuber yield under different fertilizer treatment combinations in the same dahlia cultivar and field experiment. That trade-off is practically important because dahlia growers often have to decide whether a given season is primarily about cut-flower production or tuber production, and this study provides evidence that the fertility program appropriate for each goal may differ. Read alongside KC-0819 and KC-0066, it reinforces the broader pattern across this cluster: different nutrient inputs shift dahlia allocation in different directions, and the production goal should drive the fertility decision.

Publication Type

Journal Article

Full Citation

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

Study System

Dahlia variabilis cv. 'Pink Attraction' grown under temperate field conditions.

Experimental Context

Field cultivation trial combining inorganic nitrogen and phosphorus fertilizers with biofertilizer inoculants to evaluate effects on plant growth, flowering duration, flower weight, and vase life.

Experimental Design

Factorial randomized block design with nitrogen at 50, 75, and 100 kg per hectare; phosphorus at 100 and 125 kg per hectare; and biofertilizer treatments including Bacillus, Pseudomonas, and Azotobacter.

Key Results

The combination of nitrogen at 75 kg per hectare, phosphorus at 100 kg per hectare, and Azotobacter maximized plant growth, flowering duration, flower weight, and vase life.

Mechanistic Insight

Synergistic interaction between balanced nutrient supply and biofertilizer-enhanced nutrient uptake and growth regulation produced the best outcomes. The moderate nitrogen rate outperformed both the lower and higher rates in combination with Azotobacter and the lower phosphorus level, indicating that nutrient balance rather than maximum input rate drove the best results.

Practical Guidance

In this temperate field trial, moderate nitrogen and phosphorus rates combined with Azotobacter inoculation optimized dahlia growth and flower quality. The result supports using biofertilizer inoculants as a complement to moderate inorganic fertility rather than as a substitute for it.

Why This Source Matters

This study adds vase life to the list of outcomes influenced by fertility management in dahlias, a trait that most INM studies in this collection do not measure. The finding that a moderate nitrogen rate with Azotobacter outperformed both lower and higher nitrogen rates for vase life and flower weight is consistent with the broader theme in this collection that the optimum fertility outcome in dahlias is achieved through balance rather than maximum input. It is also the only study in the INM cluster conducted under temperate rather than subtropical or tropical agro-climatic conditions, which adds a degree of geographic context diversity to the cluster.

Publication Type

Experimental Research Article

Full Citation

Barik, I. (2017). Effect of N, P, K and organic manures on flower yield and flower quality of dahlia (Dahlia variabilis) hybrid 'Eternity sports'. Environment and Ecology, 35(4E), 3664–3668.

Study System

Dahlia variabilis hybrid 'Eternity Sports' grown under field conditions during the rabi season.

Experimental Context

Field trial comparing inorganic NPK fertilizer with farmyard manure, vermicompost, and poultry manure in various combinations for effects on flowering, cut-flower quality, flower yield, tuber number, and tuber yield.

Experimental Design

Randomized block design with 13 treatments and three replications. Treatments included a control, full NPK, 75% NPK with 25% organic manure sources, 50% NPK with 50% organic manure sources, 25% NPK with 75% organic manure sources, and an equal combination of farmyard manure, vermicompost, and poultry manure.

Key Results

The 50% NPK plus 50% vermicompost treatment recorded the highest flowering duration, flower stalk length, flower diameter, flower longevity on plant, vase life, flowers per plant, flowers per plot, flowers per hectare, tubers per plant, tubers per plot, and tuber yield per plant, per plot, and per hectare. The 50% NPK plus 50% poultry manure treatment recorded the highest single flower weight and single tuber weight.

Mechanistic Insight

The source attributes improved performance under the 50% NPK plus 50% vermicompost treatment to balanced nutrient availability, improved root proliferation, enhanced microbial activity, improved NPK uptake, and enhanced photosynthetic activity. The higher individual flower and tuber weight under 50% NPK plus 50% poultry manure is attributed to nutrient solubilization during composting and bacterial activity in chicken manure.

Practical Guidance

Application of 50% NPK plus 50% vermicompost per hectare was the most broadly beneficial treatment for plant growth, flower yield, tuber yield, and flower quality in this trial. Application of 50% NPK plus 50% poultry manure was advantageous specifically for individual flower weight and tuber weight. Growers optimizing for total yield should consider the vermicompost combination; those targeting the largest individual flowers or tubers may find the poultry manure combination preferable.

Why This Source Matters

This study compares not just inorganic versus organic inputs but multiple organic manure sources — farmyard manure, vermicompost, and poultry manure — within the same trial, which allows a direct comparison of organic source effects on the same cultivar under the same conditions. The finding that different organic sources produced different outcome profiles (vermicompost for total yield and flowering duration, poultry manure for individual flower and tuber size) is a more nuanced result than most INM studies deliver. It also extends the pattern established in KC-0066 and KC-0017: that partial substitution of synthetic fertilizer with organic inputs can produce results equal to or better than full inorganic NPK across multiple dahlia outcome dimensions simultaneously.

Publication Type

Experimental Research Article

Full Citation

Vlad, I., Vlad, M., & Ioana, V. (2013). The influence of phase fertilization on Dahlia flowers quality and yield. Analele Universității din Oradea, Fascicula: Protecția Mediului, 20, 91–94.

Study System

Dahlia variabilis 'Golden Wonder' grown for cut flowers under nursery production conditions in north-western Romania.

Experimental Context

Nursery production trial conducted during 2010–2012. Plants were propagated from cuttings rooted in peat and sand substrate and then planted in nursery soil for cut-flower production.

Experimental Design

Foliar fertilization treatments used Wuchsal with an N:P:K ratio of 1:2:1 and included an unfertilized control, 0.1% applied weekly, 0.1% applied every two weeks, 0.2% applied weekly, 0.2% applied every two weeks, 0.25% applied weekly, 0.25% applied every two weeks, and 0.3% applied every two weeks. Weekly treatments received 20 fertilizations; every-two-weeks treatments received 10 fertilizations.

Key Results

Flower yield ranged from 68 stalks per square meter in the unfertilized control to 128 stalks per square meter with 0.25% Wuchsal applied weekly, an 88% increase over the control. Weekly 0.2% fertilization produced a 76% yield increase over the control. Weekly 0.2% and 0.25% treatments were reported as extremely significant compared with the control. The 0.1% every-two-weeks treatment produced 90 stalks per square meter and was not statistically significant compared with the control. First-quality flowers accounted for 72% of the unfertilized control yield and more than 80% of the yield in fertilized treatments.

Mechanistic Insight

Foliar fertilization influenced both the total number of cut-flower stems produced and the proportion classified as first quality. Application frequency mattered as much as concentration: the 0.1% every-two-weeks treatment was not significantly better than the control despite delivering the same total nutrient load over fewer applications, indicating that application interval is a meaningful variable independent of total nutrient quantity delivered.

Practical Guidance

In this nursery cut-flower trial, 0.25% Wuchsal applied weekly produced the greatest yield increase and the highest proportion of first-quality stems. Reducing concentration to 0.2% weekly still produced a substantial yield improvement. The minimum effective application frequency was weekly; every-two-weeks applications at the lowest concentration did not produce a statistically significant yield response.

Why This Source Matters

This study is the only source in this collection to evaluate application frequency as a variable in dahlia foliar fertilization, and the results show that frequency is not simply a delivery convenience — it is a production variable with measurable yield consequences. The same nutrient applied less frequently produced no significant yield improvement at the lowest concentration. That finding gives growers who use foliar fertilization a specific practical parameter: regular, frequent application at an effective concentration outperforms infrequent application at the same or higher concentration. The quality data — showing an increased proportion of first-quality stems in fertilized treatments — extends the result beyond raw yield to a commercially relevant outcome.

Publication Type

Journal Article

Full Citation

Kashif, M., Rizwan, K., Khan, M. A., & Younis, A. (2014). Efficacy of macro and micro-nutrients as foliar application on growth and yield of Dahlia hybrida L. (Fresco). International Journal of Chemical and Biochemical Sciences, 5, 6–10.

Study System

Dahlia hybrida cv. 'Fresco' grown under field conditions at the Floriculture Research Area, Institute of Horticultural Sciences, University of Agriculture, Faisalabad, Pakistan.

Experimental Context

Field experiment conducted during the 2011–2012 growing season evaluating vegetative and reproductive responses to foliar applications of macro- and micro-nutrient formulations with different NPK ratios and micronutrient compositions.

Experimental Design

Randomized complete block design with four foliar treatments and three replications, with ten plants per treatment. Treatments: T0, untreated control; T1, NPK 17:17:17; T2, NPK 15:32:7 plus Micro Power (N 1%, K₂O 1%, Zn 2.5%, B 1%, Fe 1%, Mn 1%, Cu 2%); T3, NPK 15:32:7 plus chelated mix micro-nutrients (Zn 1.5%, B 2%, Fe 2%, Mn 2%, Cu 1%). All foliar treatments were applied at 6–8 ml per 100 ml beginning 40 days after transplanting, with two subsequent applications at 15-day intervals. Parameters measured included plant height, leaf area, number of leaves per branch, number of branches per plant, branch length, number of tubers per plant, bud diameter, flower diameter, blooming period, fresh and dry weight of flower, days to first flower emergence, and number of flowers per plant.

Key Results

All foliar treatments improved measured traits relative to the untreated control. T1 (NPK 17:17:17) produced the highest number of flowers per plant (12.8 vs. 7.68 in control), the largest flower diameter (8.06 cm vs. 5.44 cm), the greatest bud diameter, the highest fresh flower weight (3.54 g vs. 2.51 g), the highest dry flower weight, and the most leaves per branch. T2 (NPK 15:32:7 plus Micro Power) produced the greatest leaf area, the most branches per plant (21.9 vs. 12.5 in control), the longest blooming period (50.3 days vs. 28 days in control), the earliest days to first flower emergence (92.3 days vs. 117 days in control), and the highest number of tubers per plant (6.63 vs. 2.88 in control). T3 (NPK 15:32:7 plus chelated micro-nutrients) produced the greatest plant height (30.3 cm vs. 23.9 cm in control) and the longest branch length. Tuber production across treatments ranked T2 (6.63) > T3 (5.87) > T1 (4.66) > T0 (2.88).

Mechanistic Insight

The source attributes improved growth to enhanced photosynthetic and metabolic activity leading to increased production of cell-division and elongation metabolites. The pattern across treatments reflects differences in nutrient profiles: the balanced equal-ratio NPK of T1 favored flower size and number, while the higher-phosphorus formulations with added micronutrients in T2 and T3 shifted responses toward vegetative architecture, tuber initiation, and bloom duration. The source does not provide a mechanistic explanation for the tuber response but reports that foliar macro- and micro-nutrient application increased tuber number across all treated plants relative to the control.

Practical Guidance

In this field trial, NPK 17:17:17 applied foliarly maximized flower size, flower number, and fresh flower weight, making it the strongest treatment for cut-flower and ornamental display goals. The NPK 15:32:7 plus micronutrient treatments extended blooming period and increased tuber number, suggesting a possible advantage for growers prioritizing season length or tuber production. Formulation choice should be matched to production goal, assessed against existing soil fertility and micronutrient status, and verified by local trial before broad application.

Why This Source Matters

This is the only study in this collection to compare multiple commercial foliar formulations — balanced NPK, high-phosphorus NPK plus broad-spectrum micronutrients, and high-phosphorus NPK plus chelated micronutrients — against each other and an untreated control within the same dahlia field experiment. The results show that different formulations produce measurably different outcome profiles: equal-ratio NPK favored bloom size and number, while higher-phosphorus formulations with micronutrients extended season length and increased tuber production. That formulation-specificity finding is directly useful for growers who use foliar feeding as part of a fertility program and need to match product choice to a production goal rather than treating all foliar fertilizers as interchangeable. Read alongside KC-0897, this study shifts the final cluster from a single observation about application frequency to a more complete picture of foliar fertilization as a practice with multiple decision variables: what to apply, how often, and at what concentration.

The Knowledge Card summaries in this collection were developed through the Dahlia Doctor research workflow from 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.