ASHS 2025 Conference

Ranunculus are sensitive to high soil salinity and to high chloride concentrations. A trial was set up in fall 2024 at the Flower Fields in Carlsbad, CA to evaluate the yield and quality parameters of field-grown ranunculus under three irrigation water treatments and corresponding increasing levels of water salinity. The treatments were 1) Municipal water, currently used at the Flower Fields to grow ranunculus and other crops; 2) a 50:50 blend of municipal water and reclaimed municipal water; 3) 100% reclaimed water (called hereafter “recycled”). The objective of the study was to investigate if a blend of municipal and reclaimed water or 100% reclaimed water can be used in the future to grow ranunculus at the flower fields. The expected salinity levels in the water, measured as electrical conductivity before fertilizer injection were

Floriculture supply chains are undergoing a shift toward sustainability, driven by consumer demand and industry initiatives to reduce environmental impacts. While previous research has explored the carbon footprint of some ornamental horticultural products, domestic U.S. cut flower production and distribution remains largely understudied. Understanding the emissions associated with different supply chain models can guide sustainable practices in the domestic floriculture industry. This study examines the carbon emissions from the production and transportation of one representative cut flower species – snapdragon. Two primary distribution models were compared: point-to-point delivery where individual growers supply retailers directly and the hub-and-spoke system where wholesale hubs consolidate and distribute flowers. By evaluating data collected from 188 growers, 330 retailers, and six regional wholesale hubs, the research quantifies carbon emissions at each stage of the supply chain. The life cycle analysis uses openLCA software to standardize emissions data to an "emissions per stem" metric, aligning with horticulture footprinting standards. The results highlight the importance of optimizing supply chain logistics to reduce emissions. Furthermore, applying the social cost of carbon ($185 per metric ton of CO2) provides an economic perspective on the environmental impact of floral supply chains. As businesses move toward more climate-conscious operations, these insights can guide decisions that align with both financial and sustainability business goals.

Caladiums (Caladium x hortulanum) are popular ornamental plants prized for their vibrant foliage and unique patterns. The great majority of caladium tubers used by the U.S. and the world are produced in Florida. The tuber production process typically begins in March, with harvesting taking place between November and February. During this period, plants are exposed to high temperatures, high radiation, high relative humidity, heavy rainfall, and tropical storms, resulting in multiple stresses on the plants. Research in other crops has demonstrated the effectiveness of clay-based products in reducing leaf temperatures and protecting plants from environmental and/or biological stresses. This study aimed to assess the plant growth, quality, and tuber production of five caladium cultivars ('Tapestry', 'Lava Glow', 'Wonderland', 'Pink Panther', and 'Summer Pink') under different kaolin clay treatments. Field-grown plants were sprayed throughout the season with either kaolin, kaolin with red dye, or left untreated (control) to assess their response. An adjuvant was added to prevent excessive washout from rainfall. Data collected over two seasons included plant height, canopy coverage, and volume (per plot) extracted from multispectral images captured by a small uncrewed aerial system, leaf temperature using an infrared thermometer, chlorophyll content using a SPAD meter, and subjective ratings for plant color display, leaf health, and plant fullness using a scale from 1 to 5. At harvest, tuber production was evaluated through fresh weight, dry weight, and production index. Results showed that the growth curves for plant height, canopy coverage, and volume exhibited a bell-shaped curve, with an initial linear growth and a maximum peak in early to mid-September for most cultivars, except 'Summer Pink', which peaked later. Treatment differences were not statistically significant, with cultivar variations being the primary factor. However, kaolin and kaolin red treatments effectively reduced leaf temperatures during the 2023 production season, with kaolin red also receiving a higher rating for color display. Plants under kaolin treatments displayed lower chlorophyll content compared to untreated plants. Tuber production was unaffected by the treatments but showed differences among the cultivars, with 'Tapestry' producing the highest tuber dry weight. The production index, which accounts for tuber grading, number, and relative economic values, revealed that 'Summer Pink' had the highest value compared to 'Tapestry'. This study provides valuable insights into the growth behavior of caladium cultivars and the potential benefits of using kaolin treatments as a crop protection strategy.

Peatmoss, a commonly used substrate component, is facing numerous challenges to remain a sustainable option for horticultural production. Due to mounting factors such as weather-limited harvesting, increasing transport costs, waning public acceptance, and now potential international tariffs, many are searching for alternative materials to replace some of the peatmoss in their operations. Biochar is one such alternative that may present numerous benefits as a peat alternative in container production. Biochar is the product of the pyrolysis of biomass (commonly agricultural residues) in an oxygen limited environment, resulting in a product that has increased porosity, increased water and nutrient retention, and can be produced regionally from a number of sources. Incorporating biochar into container production can reduce peat use and improve nutrient retention. However holistically blending can prove costly and alter the substrate physical properties, requiring major changes to production practices, an obstacle that can be considered a barrier. The use of stratification has been shown to successfully reduce peat use while maintaining highly productive growing conditions. With stratification, growers can incorporate alternative materials strategically in the container while limiting the associated costs. Therefore, this study was designed to evaluate the effect of sugarcane bagasse biochar on nutrient retention in both stratified and non-stratified peat-based container systems. Nine peat-based substrate treatments were utilized in this study, with either the entire container filled with peat-based substrate or stratified above a pine bark or hammermilled wood fiber. Within each substrate, sugarcane bagasse biochar was amended at 0 (control) or 10% of the container volume, by either blending throughout the container or blending at 20% upper strata only (equivalent to 10% by vol. overall). Petunia plugs were planted into 3.8 L containers filled with each of these different substrate treatments. The plants were placed on two different fertilizer regimes, with plants receiving either 100 ppm or 300 ppm fertilizer once a week. Leachate was collected biweekly to assess the impact on nutrient retention. Plant growth and nutrition were assessed. The incorporation of biochar has not significantly impacted plant growth; however, it has improved nutrient retention. Biochar improved nutrient retention in the plants stratified with wood fiber in both the high and low fertilizer regimes, while improving nutrient retention in stratified bark in the high fertilizer regime. The results indicate that strategic inclusion of biochar may reduce fertilizer application frequency.

Our objective was to evaluate the efficacy of benzyladenine or ethephon foliar spray applications to control growth and improve branching of ‘Dragon Wing® Red’ begonia (Begonia interspecific). On 10 Sep 2024, a 288-cell plug tray of ‘Dragon Wing® Red’ begonia was received from a commercial propagator. Plugs were transplanted into 15.2-cm-diameter containers filled with a commercially available soilless peat-based substrate. Plants were grown in a glass-glazed greenhouse under supplemental and day-extension lighting provided by 780-W light-emitting diode lamps from 0600 to 2200 HR (16-h photoperiod) with an air temperature set point of 20 °C. At 7 d after transplant, 10 single-plant replicates were treated with a solution containing benzyladenine or ethephon and a surfactant. Plants received a foliar spray (vol. 0.2 L·m–2) containing deionized water (0 mg·L–1; untreated) or 10, 30, 50, 70, or 90 mg·L–1 benzyladenine or 125, 250, 500, 750, 1,000, or 2,000 mg·L–1 ethephon. Benzyladenine and ethephon foliar spray applications influenced begonia growth and development differently. Benzyladenine concentrations increasing from 10 to 90 mg·L–1 suppressed growth index, an integrated measurement of height and diameter, by 1% to 3%, respectively, compared to untreated plants. Branch number increased by 32% to 64% (3 to 5 branches) as concentrations increased from 30 to 90 mg·L–1 benzyladenine compared to untreated plants. Shoot dry weight (SDW) decreased as benzyladenine concentrations increased, but time to flower (TTF) was unaffected. Ethephon concentrations increasing from 125 to 2,000 mg·L–1 influenced plant height, plant diameter, growth index, branch number, SDW, and TTF. Growth index was suppressed as ethephon concentrations increased from 125 to 2,000 mg·L–1, resulting in plants that were 11% to 30% smaller than untreated plants. Compared to untreated plants, ethephon concentrations increasing from 125 to 1,000 mg·L–1 improve branching with 1 to 2 more branches developed per plant. Ethephon concentrations of 125 to 2,000 mg·L–1 limited SDW by 23% to 49% compared to untreated plants. Time to flower was delayed by 3 to 10 d as concentrations increased from 125 to 2,000 mg·L–1 ethephon. Begonia plants sprayed with ≥750 mg·L–1 ethephon developed phytotoxicity and had reduced ornamental quality. Our results indicate that growers can attain growth control and enhance branching with foliar spray applications of 30 to 90 mg·L–1 benzyladenine or 125 to 500 mg·L–1 ethephon, but these should be used as an initial range for trials during greenhouse production.

Ethephon substrate drenches have been shown to effectively control growth of annual bedding plants and herbaceous perennials. However, research has shown the efficacy of ethephon substrate drenches is impacted by the time of application. Therefore, the objective of our research was to evaluate how ethephon substrate drenches impact growth when applied at varying times post-transplant. Young plants of lobed tickseed (Coreopsis ×hybrida Big BangTM ‘Mercury Rising’) and coleus [Coleus scutellarioides (L.) Benth. ‘Main StreetTM Bourbon Street’] were transplanted into 12.7-cm containers filled with a soilless peat-based substrate. At 3, 7, 10, 14, 17, or 21 d after transplant, 8 single-plant replicates received a single substrate drench of 90 mL aliquots of a solution containing 0, 25, 50, 100, or 200 mg·L–1 ethephon. Plants were grown in a glass-glazed greenhouse for 5 to 7 weeks after initial drench application before growth and morphological data including plant height, plant diameter, shoot dry weight (SDW), and root dry weight (RDW) were determined. In general, increasing concentrations of ethephon influenced plant height, plant diameter, SDW, and RDW of coleus and lobed tickseed. In Expt. 1, plant size (height and diameter) and biomass accumulation (SDW and RDW) of coleus was significantly influenced by increasing concentrations of ethephon, with the effects diminishing as application time was delayed. For example, as concentrations increased from 0 to 200 mg·L–1 ethephon, coleus treated at 3 days after transplant (DAT) were 33% (5.3 cm) shorter, while those treated at 17 DAT were 21% (3.6 cm) shorter. Shoot dry weight of coleus drenched with 200 mg·L–1 ethephon at 3 or 21 DAT were 50% (2.0 g) and 23% (1.0 g) lower, respectively, compared to untreated plants. Compared to untreated plants, RDW of plants drenched with 200 mg·L–1 ethephon 3 or 14 DAT was 65% (2.8 g) and 50% (2.6 g) smaller, respectively. In Expt. 2, plant height was unaffected by increasing concentrations of ethephon, but plant diameter and biomass accumulation of lobed tickseed was significantly affected. For example, as concentrations of ethephon increased from 0 to 200 mg·L–1, lobed tickseed treated 3 and 21 DAT were 8% (2.4 cm) and 9% (2.8 cm) narrower, respectively, compared to untreated plants. Overall, the magnitude of control diminished as application time increased and negative phytotoxic effects were seen in early applications (≤7 d). Therefore, we suggest applying ethephon substrate drenches 7 to 14 d after transplanting.

Calcium phosphate [Ca₃(PO₄)₂] is an nonlabile form of phosphorus (P) commonly found in substrates with a basic pH and it is not available for plant uptake. Phosphate solubilizing bacteria (PSB) are plant-associated microorganisms that can solubilize calcium phosphate by secreting organic acids. PSB inoculation alleviates P deficiency symptoms including leaf purpling, and PSB inoculum can be amended with substances that may improve PSB performance (i.e. glucose). Our goal was to evaluate the efficacy of PSB isolated from the rhizosphere of greenhouse ornamentals (Pantoea trifolii C2B11, Pantoea formicae C8D10, Pantoea sp. C2G6 and Enterobacter soli C4A1) in substrate with pH 6.0 or 6.5, and with an inoculum amended with glucose (10 g·L-1), Luria Bertani (LB) broth (111 mL·L-1), or humic and fulvic acids (20 g·L-1). An experiment was conducted using French marigold 'Durango Yellow' (Tagetes patula) fertilized once per week with 200 mg·L-1 N from a 15N-0P-12.5K-2.9Ca-1.2Mg fertilizer. P was supplemented to the fertilizer solution as Ca3(PO4)2 at 10 mg·L-1 P. Bacillus velezensis was included as a positive control. Digital biomass, Normalized Pigment Chlorophyll Ratio Index (NPCI), Plant Senescence Reflectance Index (PSRI) and canopy hue (color) were measured with the TraitFinder, a digital phenotyping workstation. NPCI and PSRI values from healthy foliage are low but increase under stress. At pH 6.0, all marigolds receiving PSB had increased growth regardless of the inoculum amendments. PSB amended with glucose resulted in marigolds with a lower NPCI than non-inoculated plants. Additionally, PSB-treated marigolds had a higher proportion of green canopy, and a lower proportion of red canopy compared to non-inoculated marigolds when the inoculum was amended with glucose or not amended. At pH 6.5, all PSB resulted in increased marigold growth regardless of inoculum amendments. PSB treated marigolds were healthier than non-inoculated plants, as indicated by their lower NPCI and PSRI values, regardless of the inoculum amendments. Accordingly, PSB treated marigolds had a higher proportion of green canopy and a lower proportion of red canopy compared to non-inoculated marigolds. Bacterial effects were more consistent when inoculum was supplemented with LB. A greater benefit was observed in plants grown at pH 6.5. Microbiome analysis of the rhizosphere showed that inoculation with C2B11, C2G6, and C8D10 increased the relative abundance of the genus Pantoea, and C4A1 enriched the genus Enterobacter. Careful determination of optimal inoculum supplements is key to developing efficient inoculants that promote growth in greenhouse ornamentals.

Supplying adequate iron (Fe) to greenhouse crops is challenging, particularly for iron-sensitive plants grown in soilless substrates under alkaline conditions. High pH levels reduce Fe bioavailability by promoting the formation of insoluble iron hydroxide (Fe(OH)₃), which limits plant uptake. Plant growth-promoting bacteria (PGPB) enhance plant growth and stress tolerance through diverse mechanisms, including siderophore production. Siderophores are small molecules that have a high affinity for metal ions like ferric iron (Fe³⁺). Once the siderophore chelates iron, the complex is soluble, and plant roots can readily absorb it. This study identified siderophore producing bacteria (SPB) capable of enhancing plant growth under Fe-limiting conditions. A rhizosphere bacterial collection from greenhouse plants was screened for siderophore production using the chrome azurol S (CAS) assay. Genomic analysis of 12 isolates identified in the CAS assay revealed diverse siderophore-related genes and other plant growth-promoting traits. Five of the isolates (C2G2, C5A12, C6E3, C8G7, and C10A8) were identified as strong candidates based on their siderophore-related genes and Fe uptake pathways. A ferrozine-based assay confirmed Fe solubilization in a modified Hoagland’s solution containing goethite (Fe³⁺O(OH)) as an insoluble Fe source, with bacterial treatments yielding 0.57 mg Fe L⁻¹ versus 0 mg Fe L⁻¹ in controls (no bacteria). Subsequent in planta experiments evaluated the impact of SPB on French marigold ‘Durango Yellow’ (Tagetes patula) growth in hydroponic systems under Fe-limiting conditions. French marigold proved to be a good model plant for this screening system. Digital phenotyping showed that plants inoculated with isolates C5A12, C8G7, or C10A8 had 53.0%, 45.7%, or 50.3% more green leaf tissue, respectively, compared to untreated control plants. Additionally, treated plants had increased root biomass. These findings demonstrate the potential of SPB to enhance Fe availability and plant growth under iron-limiting conditions and offer a novel strategy for improving greenhouse crop production. The incorporation of SPB into greenhouse practices may benefit Fe-sensitive crops or systems where pH fluctuations reduce Fe availability, ultimately improving crop quality and sustainability.

Increased interest in peat-alternative substrates has contributed to the development of both regional and global wood substrates. Utilizing different manufacturing equipment to produce wood fiber components allows producers to modify wood fibers/inputs through chipping, milling, heat, pressure, or various combinations, to alter physical properties and yield suitable material for horticulture use. Commercial substrates available for plant production include peat-reduced formulas with various percentages (by volume) of wood fiber. Current lime amendment suggestions to bring substrates into the optimal pH range for plant growth are based on peat as the main component. Wood fiber has variable initial pH across manufactured type and reacts differently to lime amendments compared to peat. To aid in the understanding of lime amendments to wood fiber substrate blends, this study was designed to measure the pre-plant pH response over time of substrates influenced by wood component type, peat inclusion percentage, and dolomitic lime amendment rate. Three types of manufactured wood substrates (hammermilled, screw-extruded, and disc refined) were individually blended with Sphagnum peat at 20% increments (20, 40, 60, 80, and 100%). Each substrate was amended with 0, 4, 8, or 12 lbs/yd3 dolomitic lime and incubated in plastic bags to measure pH change at 0, 1, 3, 5, 7, 14, 21, and 28 days after blending. Resulting pH values indicate dolomitic lime amendment rates will need to be adjusted based on peat:wood volume ratios. Wood fiber exhibited a higher initial pH than Sphagnum peat and within blends, as wood fiber rate increased, pH increased across all lime rates. Dolomitic lime amendments should be closely monitored at 40% volume or more wood fiber. Moderate pH differences were measured between manufactured wood fiber type within the same peat:wood volume ratio and lime rate, emphasizing interchangeability of wood component type.

Frass is the left-over substrate produced from mass rearing insects as food and feed. Black soldier fly (Hermetia illucens) larvae frass has become a popular option for vegetable production as a potential fertilizer and peat replacement. Controlled environment propagation of ornamental crops requires large amounts of peat, therefore researching alternative substrates has a rising interest for growers. Pansies (Viola x wittrockiana), Marigold ‘Inca II’(Tagetes erecta), and Marigold ‘Safari’(Tagetes patula) were grown in growth chambers to evaluate the incorporation of frass into peat based substrates for ornamental production: 3 treatments from previous studies (BSF 10, 20, and 30%), 1 treatment included to assess the impact of leaching on frass (BSF 40-), and a 100% peat control (CP 100%). Pansies grown in the BSF treatments of were statistically comparable to the control in all parameters except, root weight. Pansy root weight was significantly higher in the treated BSF 40- treatment. BSF 40% produced the lowest values in all crops and parameters, except for Marigold ‘Inca’ root weight, where only BSF 40- was significantly higher. BSF 40- was significantly greater or equal to the control in all crops and parameters, except for Marigold ‘Safari’ plant size and root weight. Chlorophyll concentrations were statistically comparable across all treatment and control in all crops. Past research and this study generally indicate that at large concentrations, like 40%, frass can have negative outcomes for crop production in peat based substrates. However, due to the success of our leached treatment, BSF 40-, it seems frass can be utilized at larger concentrations, but additional alterations may be required before mixing into growing medias and substrates. Additionally, certain crops appear to have more neutral and positive reactions to frass incorporation. Engaging efforts to target ideal crops will improve the application and practicality of this research.

Phosphorus (P) is an essential macronutrient required for plant growth. In fertilizers used for soilless substrates, P is in the form of phosphate and is readily leached from containers leading to environmental contamination. The FeSO4 bridge method has been proposed to reduce P losses by forming insoluble iron-phosphate complexes that retain P within the substrate, but reduced bioavailability may limit plant growth. The aim of this research was to evaluate the FeSO4 bridge method in combination with inoculation of the substrate with phosphate-solubilizing bacteria (PSB) and siderophore-producing bacteria (SPB) to gradually release P for plant uptake. An experiment was conducted to evaluate the growth of marigolds ‘Durango Yellow’ (Tagetes patula) using a substrate composed of 80% peat and 20% perlite by volume, with substrate either amended or not amended with 3.0 kg·m-3 FeSO4·7H2O. After transplanting, plants received 100 mg·L-1 N from 15N-2.2P-12.5K-2.9Ca-1.2Mg Jack’s Professional water-soluble fertilizer as the P source for two weeks to promote the formation of iron-phosphate complexes. Additionally, two bacterial application strategies were evaluated: one starting from transplanting and another applied when P deficiency symptoms appear, with three weekly inoculations each. The bacterial treatments included: a control without bacterial inoculation; three PSB strains, Bacillus megaterium (C3F10), Pantoea rwandensis (C3A8), and Pseudomonas sp. (C6E7); one SPB strain Pseudomonas soli (C10A8); and a commercial inoculum of Bacillus velezensis (from the biostimulant LalRise Vita, Lallemand, Inc). Plants were grown under controlled greenhouse conditions, with weekly measurements of spectral variables and morphological parameters using the TraitFinder digital phenotyping system. Leachate was collected using the pour-through method and analyzed for P concentrations using ion chromatography. The results confirmed that the FeSO4 bridge method formed iron-phosphate complexes, reducing P leaching when amending the substrate with 3.0 kg·m-3 FeSO4·7H2O compared to non-amended substrate. Visual differences in plant growth were observed among treatments, with better outcomes when bacterial inoculation started at transplanting. In contrast, plants that received bacterial treatment after symptoms appeared could not recover, showing significantly reduced visual quality. Among the bacterial treatments, Pseudomonas soli (C10A8) promoted the highest biomass accumulation and spectral variables such as hue and green leaf index (GLI) indicated improved visual quality compared to the control (no bacteria) and other bacterial strains. These findings demonstrated that amending soilless substrates with FeSO4, combined with bacteria like Pseudomonas soli (C10A8), enhances P retention while promoting plant growth. This method offers growers a practical approach to reducing environmental impact while maintaining crop quality.