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Our objective was to quantify foliar ethephon application effects on flowering and growth of several streptocarpus (Streptocarpus ×hybridus) cultivars. ‘Ladyslippers Blue Halo’, ‘Ladyslippers Deep Blue Vein’, and ‘Ladyslippers Red Rose’ streptocarpus were planted in 6-inch containers filled with a soilless substrate. Foliar spray applications of solutions containing 0, 125, 250, 500, or 1000 mg·L⁻¹ ethephon were applied either 2 weeks after planting (one application) or 2 and 4 weeks after planting (two applications). After 13 weeks, the total number of inflorescences was recorded and the growth index (GI) and time to flower were calculated. The efficacy of ethephon sprays depended on the concentration, number of applications, and cultivar. A single application of 250 to 1000 mg·L⁻¹ ethephon delayed flowering of ‘Ladyslipper Deep Blue Vein’ by 9 to 27 days, whereas one application of 1000 mg·L⁻¹ applied to ‘Ladyslipper Red Rose’ delayed flowering by 9 days. Similarly, two applications of any ethephon concentration delayed flowering of ‘Ladyslipper Deep Blue Vein’ by up to 37 days, while flowering of ‘Ladyslipper Red Rose’ was delayed by 17 days when 1000 mg·L⁻¹ was applied. The GI of ‘Ladyslipper Deep Blue’ and ‘Ladyslipper Red Rose’ was unaffected by ethephon and, while the GI of ‘Ladyslipper Blue Halo’ was smaller than untreated plants when one or two applications of 500 or 1000 mg·L⁻¹ ethephon was applied; these smaller plants were still of marketable size and quality. We conclude that ethephon may be used to delay flowering and reduce the number of inflorescences formed before finishing with minimal impact on finished plant size.

Our objective was to quantify the efficacy of foliar plant growth retardant applications on plant height and time to flower of seed-propagated new guinea impatiens (Impatiens hawkeri) produced in packs and flats. ‘Divine Cherry Red’, ‘Divine Scarlet Bronze Leaf’, and ‘Divine White Blush’ seedlings were planted in 1801-cell packs. Seven days after planting, deionized water (control) or solutions containing ancymidol (15 to 60 mg·L⁻¹), chlormequat chloride (750 to 3000 mg·L⁻¹), daminozide (1250 to 5000 mg·L⁻¹), ethephon (250 to 1000 mg·L⁻¹), flurprimidol (10 to 40 mg·L⁻¹), paclobutrazol (10 to 40 mg·L⁻¹), or uniconazole (5 to 20 mg·L⁻¹) were applied to seedlings. A second experiment was performed with the same cultivars quantifying the growth and development in response to a broader range of flurprimidol or paclobutrazol (5 to 40 mg·L⁻¹) or uniconazole (2.5 to 20 mg·L⁻¹) sprays. Plant height was measured 7 weeks after planting. For Expt. 1, ancymidol, chlormequat chloride, and daminozide had little to no impact on stem elongation. However, flurprimidol, paclobutrazol, and uniconazole suppressed height at flowering of all three cultivars. In Expt. 2, plant height with concentrations flurprimidol, paclobutrazol, or uniconazole up to 27 to 30, 20 to 30, or 4 to 5 mg·L⁻¹, respectively, depending on the cultivar. Five to 20 mg·L⁻¹ flurprimidol or paclobutrazol, or < 2.5 mg·L⁻¹ uniconazole may be used to control stem elongation of seed-propagated new guinea impatiens for production in flats.

Our objectives were to quantify the growth and quality of herbaceous annuals grown in different types of bioplastic-based biocontainers in commercial greenhouses and quantify producer interest in using these types of biocontainers in their production systems. Seedlings of ‘Serena White’ angelonia (Angelonia angustifolia) and ‘Maverick Red’ zonal geranium (Pelargonium ×hortorum) that had been transplanted into nine different (4.5-inch diameter) container types [eight bioplastic-based biocontainers and a petroleum-based plastic (PP) (control)] were grown at six commercial greenhouses in the upper midwestern United States. Plants were grown alongside other bedding annuals in each commercial greenhouse, and producers employed their standard crop culture practices. Data were collected to characterize growth when most plants were flowering. Questionnaires to quantify producer perceptions and interest in using bioplastic-based biocontainers, interest in different container attributes, and satisfaction were administered at select times during the experiment. Container type interacted with greenhouse to affect angelonia growth index (GI) and shoot dry weight (SDW), as well as shoot, root, and container ratings. Container type or greenhouse affected geranium GI and shoot rating, and their interaction affected SDW, and root and container ratings. These results indicate that commercial producers can grow herbaceous annuals in a range of bioplastic-based biocontainers with few or no changes to their crop culture practices.

We evaluated the effects of seven types of 4.5-inch top-diameter biocontainers and five rates of paclobutrazol drench on the growth and development of angelonia (Angelonia angustifolia ‘Serena White’) and petunia (Petunia ×hybrida ‘Wave^® Purple Improved Prostrate’) during greenhouse production. The container types included were biopolyurethane-coated paper fiber; uncoated paper fiber; rice hull; coconut coir; peat; two types of bioplastic container, one made from 90% polylactic acid (PLA) and 10% lignin [PLA-lignin (90/10 by weight)] and another made from 60% PLA and 40% soy polymer with adipic anhydride {SP.A [PLA-SP.A]; (60/40 by weight)}; and a petroleum-based plastic control. All containers were filled with 590 mL of substrate composed of (by vol) 75% canadian sphagnum moss and 25% perlite. Ten days after transplanting seedlings, 2-fl oz aliquots of deionized water containing 0, 1, 2.5, 5, 10, or 20 mg·L⁻¹ paclobutrazol were applied to the substrate surface as drenches. The date of anthesis was recorded for each plant, and growth data were collected 6 weeks after transplant. Shoots were harvested and dried and shoot dry weight (SDW) was recorded. Height (angelonia only) and diameter of angelonia and petunia and time to flower were calculated. Container type and paclobutrazol concentration interacted to affect size and SDW of angelonia and petunia. Growth index of angelonia treated with 0 mg·L⁻¹ paclobutrazol and grown in coir and peat containers was 19% to 29% and 29% to 38% smaller than that of plants in other container types, respectively. Diameter of untreated petunia grown in peat containers was similar to that of those grown in coir and uncoated paper fiber containers, but was smaller (10.9 to 13.5 cm) than that of plants grown in other container types. As paclobutrazol concentrations increased from 0 to 20 mg·L⁻¹ treatments, SDWs of petunia grown in coir containers were suppressed by 23%, whereas plants grown in rice hull containers were up to 45% less. Our results indicate that growth suppression of angelonia and petunia grown in biocontainers using paclobutrazol drenches varies by the type of biocontainer. Producers should reduce paclobutrazol drench concentrations to produce plants of appropriate size if substituting coir or peat biocontainers for traditional petroleum plastics, whereas no adjustment in plant growth retardant (PGR) drench concentrations is required for plants produced in the other biocontainer types we evaluated.

We quantified the growth and quality of ‘Arizona Sun’ blanket flower (Gaillardia ×grandiflora) grown in different bioplastic containers and characterized the interest of commercial perennial producers in using bioplastic-based biocontainers in their herbaceous perennial production schemes. Plants were grown in three types of #1 trade gallon (0.75 gal) containers at five commercial perennial producers in the upper-midwestern United States. Containers included one made of polylactic acid (PLA) and a proprietary bio-based filler derived from a coproduct of corn ethanol production, a commercially available recycled paper fiber container twice dip-coated with castor oil–based biopolyurethane and a petroleum-based plastic (control) container. Plant growth data were collected when most plants had open flowers, and plant shoots, roots, and containers were rated by commercial grower participants. Questionnaires were administered at the beginning and at the end of the experiment to characterize the perceptions and interest of growers in using these containers, their interest in different bioplastic-based container attributes, and their satisfaction from using the containers. Container type and grower interacted to affect growth index (GI), shoot dry weight (SDW), and container rating. Root rating was affected by container type or grower and shoot rating was unaffected by either. Our results indicate that commercial producers can adapt these bioplastic-based biocontainers to blanket flower production with few or no changes to their crop cultural practices.

We evaluated emerging biopolymer horticultural products that provide fertilizer nutrients to plants (fertilizing biocontainers, pelletized biopolymer fertilizer, and biopolymer fertilizer spikes) for their effectiveness during greenhouse production and garden growth of floriculture crops, and during postproduction culture of container ornamentals. Greenhouse experiments (in 4.5-inch containers) and garden trials were performed with tomato (Solanum lycopersicum), pepper (Capsicum annuum), petunia (Petunia ×hybrida), and marigold (Tagetes patula). Postproduction experiments were performed with 12-inch hanging baskets containing lobelia (Lobelia erinus), trailing petunia (Calibrachoa ×hybrida), and petunia, and with 13-inch patio planters containing zonal geranium (Pelargonium ×hortorum), spikes (Cordyline indivisa), bidens (Bidens ferulifolia), and trailing petunia. Although slightly less effective than synthetic controlled-release fertilizer (CRF), all three nutrient-containing biopolymer horticultural products were sufficient and suitable for providing fertilizer nutrients to plants grown in containers and in garden soil. Results of the postproduction experiment provided proof-of-concept for the effectiveness and potential of biopolymer fertilizer spikes as a sustainable method for providing fertilizer nutrients to containerized plants. The current formulation of pelletized biopolymer fertilizer was somewhat more effective for vegetable crops (pepper and tomato) than for floriculture crops (marigold and petunia). For plants produced in 4.5-inch containers, the combination of the fertilizing biocontainer with no additional fertilizer in the greenhouse, then burying the fertilizing container beneath the plant to degrade and provide nutrients in the garden was very effective. Biopolymer horticultural products represent a promising alternative to petroleum-based plastic containers and synthetic fertilizers. Adoption of some or all of these technologies could improve the environmental sustainability of the horticulture industry without reducing productivity or efficiency, and without increasing labor intensity.

The objective of this research was to quantify the effects of phosphorous (P) concentrations on the growth, development, and tissue mineral nutrient concentrations of four popular culinary herbs commonly grown in containers. Seedlings of sweet basil (Ocimum basilicum ‘Italian Large Leaf’), dill (Anethum graveolens ‘Fernleaf’), parsley (Petroselinum crispum ‘Giant of Italy’), and sage (Salvia officinalis) were individually transplanted to 11.4-cm-diameter containers filled with soilless substrate comprising canadian sphagnum peatmoss and coarse perlite. Upon transplanting and throughout the experiment, seedlings were irrigated with solutions containing 0, 5, 10, 20, or 40 mg·L⁻¹ P; all other macro- and micronutrient concentrations were the same across P concentrations. Plants were grown for 4 weeks in a greenhouse; after that time, data were collected. Relationships between height and width and P concentrations were nonlinear for all four species; height and width increased as P increased to more than 0 mg·L⁻¹ until the species-specific maxima; after that time, no further increase occurred. The same trend was observed for the branch length of sweet basil and sage, and for internode length, leaf area, and shoot dry mass of all four species. Although visible P deficiency symptoms were observed for plants provided with 0 mg·L⁻¹ P, there were no signs of P deficiency for plants provided with ≥5 mg·L⁻¹ P, even though tissue P concentrations were below the recommended sufficiency ranges. As a result of this research, containerized sweet basil, dill, parsley, and sage can be provided with 5 to 10 mg·L⁻¹ P during production to limit growth and produce plants without visible nutrient deficiency symptoms that are proportional to their containers.

Various types of emerging bioplastic containers present a range of physical and chemical properties and can perform differently from one another in production environments. Container performance may be affected by substrate moisture content. We quantified the effects of bioplastic container type and substrate volumetric water content (VWC) on the aesthetic and mechanical strength properties of bioplastic containers and on plant growth. Seedlings of ‘Divine Cherry Red’ new guinea impatiens (Impatiens hawkeri W. Bull) and ‘Pinot Premium Deep Red’ zonal geranium (Pelargonium ×hortorum L.H. Bailey) were transplanted into five types of 11.4-cm–diameter containers, four types made from bioplastics and one type made from petroleum-based plastic and used as a control. Plants were watered to container capacity at transplant, allowed to dry down to VWC thresholds of 0.20 or 0.40 m³·m⁻³, and subsequently maintained at desired set points by using a precision irrigation system controlled by soil moisture sensors. Total volume of water applied per plant to new guinea impatiens was affected by VWC and not container type, whereas irrigation volume was affected by both for geranium. Growth index and shoot dry mass (SDM) of new guinea impatiens and geranium were affected by VWC. Container type affected growth index and SDM of geranium only. Water use efficiency (WUE) of both species was similar regardless of container type and VWC. Aesthetic quality varied based on VWC for only one container type, which was made from a blend that included soy-based bioplastic. Containers manufactured with polyhydroxyalkanoates (PHA) and dried distiller’s grains and solubles (DDGS) or polylactic acid (PLA), soy polymer with adipic anhydride (SP.A), and a proprietary bio-based filler (BR) derived from modified DDGS were stronger when maintained at a lower VWC, 0.20 m³·m⁻³. Our findings indicate that restricting irrigation to the minimum needed to achieve the desired crop growth is a viable strategy for sustaining aesthetic quality and strength of bioplastic containers manufactured with plant protein–based fillers such as SP.A and BR. Other bioplastic containers, such as those made of PLA–lignin biocomposite, show durability equal to that of petroleum-based plastic containers and maintain pristine appearance regardless of substrate VWC during production.