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John J. Sloan, Raul I. Cabrera, Peter A.Y. Ampim, Steve A. George and Wayne A. Mackay

Organic and inorganic amendments are often used to improve chemical and physical properties of soils. The objective of this study was to determine how the inclusion of light-weight expanded shale in various organic matter blends would affect plant performance. Four basic blends of organic growing media were prepared using traditional or alternative organic materials: 1) 75% pine bark (PB) + 25% sphagnum peatmoss (PM), 2) 50% PB + 50% wastewater biosolids (BS), 3) 100% municipal yard waste compost (compost), and 4) 65% PB + 35% cottonseed hulls (CH). Light-weight expanded shale was then blended with each of these mixtures at rates of 0%, 15%, 30%, and 60% (v/v). Vinca (Catharanthus roseus), verbena (Verbena hybrida), and shantung maple (Acer truncatum) were planted into the growing media after they were transferred into greenhouse pots. Vinca growth was monitored for 3 months before harvesting aboveground plant tissue to determine total biomass yield and elemental composition. Verbena growth was monitored for 6 months, during which time aboveground plant tissue was harvested twice to determine total biomass yield. Additionally, aboveground vinca plant tissue was analyzed for nutrients and heavy metal concentrations. In the absence of expanded shale, verbena and shantung maple trees produced more aboveground biomass in the 50-PB/50-BS blends, whereas vinca grew more biomass in the pure compost blends. Inclusion of expanded shale in the various organic matter blends generally had a negative effect on plant growth, with the exception of shantung maple growth in the 65-PB/35-CH blend. Reduced plant growth was probably due to a lower concentration of nutrients in the growing media. Macro- and micronutrient uptake was generally reduced by addition of expanded shale to the organic growing media. Results suggest that organic materials that have been stabilized through prior decomposition, such as compost or PM, are safe and reliable growing media, but expanded shale offers few benefits to a container growing medium except in cases where additional porosity is needed.

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Genhua Niu, Denise S. Rodriguez and Yin-Tung Wang

The effect of drought on the growth and gas exchange of six bedding plant species—agastache [Agastache urticifolia (Benth.) O. Kuntze `Honeybee Blue'], dusty miller (Cineraria maritima L. `Silverdusty'), petunia (Petunia ×hybrida `Wave Purple'), plumbago (Plumbago auriculata Lam. `Escapade'), ornamental pepper (Capsicum annuum L. `Black Pearl'), and vinca [Catharanthus roseus (L.) G. Don `Titan']—was quantified under greenhouse conditions. Seeds were sown in January and seedlings were grown in the greenhouse until 18 Apr., when two irrigation treatments—drought (D, ≈18% volumetric moisture content at reirrigation) and control (C, ≈25% volumetric moisture content at reirrigation)—were initiated. Leaf net photosynthetic rate (Pn), stomatal conductance (gs), and transpiration (E) were determined in response to a range of substrate moisture content (from ≈5% to 30% by volume) and temperature (from 20 °C to 40 °C). Dry weight of agastache, ornamental pepper, and vinca was unaffected by drought, whereas that of other species was reduced. Leaf area of plumbago and height of plumbago and vinca were reduced by drought. As substrate moisture content decreased from 25% to 10%, Pn, E, and gs decreased linearly in all species except petunia and plumbago. Leaf net photosynthetic rate of all species declined as leaf temperature increased from 20 °C to 40 °C. In contrast, E of all species, except petunia, increased as temperature increased. Transpiration rate of petunia increased as temperature increased from 20 °C to 30 °C, and then decreased between 30 °C and 40 °C. Although petunia had the highest Pn among the tested species, its Pn and gs declined more rapidly compared with the other species as temperature increased from 20 °C to 40 °C or as substrate moisture content decreased, indicating that petunia was most sensitive to high temperature and drought.

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D. Yvette Henson, Steven E. Newman and David E. Hartley

This study was conducted to evaluate the growth, visual quality, and stress response of 17 species of bedding plants and Kentucky bluegrass (Poa pratensis L.) grown outdoors for 10 weeks during the summer of 2003 at three locations in Colorado. Plants were irrigated at 100% of the reference evapotranspiration (ET0) (amount required to maintain Kentucky bluegrass in an optimum condition) for 2 weeks followed by 8 weeks at five irrigation levels: 0%, 25%, 50%, 75%, and 100% ET0. Begonia carrieri Hort. `Vodka', Lobelia erinus L. `Cobalt Blue', and Viola ×wittrockiana Gams. `Crown Gold' grew well with a minimum of 50% or more ET0 based on Kentucky bluegrass. Impatiens walleriana Hook. fil. `Tempo White' grew well only with 100% ET0. Antirrhinum majus L. `Sonnet Yellow', Dianthus L. `First Love', Lobularia maritima (L.) Desv. `Carpet White', and Pelargonium ×hortorum L.H. Bailey performed well with 25% to 50% ET0. The species Catharanthus roseus (L.) G. Don `Peppermint Cooler', Rudbeckia hirta L. `Indian Summer', Senecio cineraria D.C. `Silver Dust', Tagetes erecta L. `Inca Yellow' and T. patula L. `Bonanza Gold', Zinnia angustifolia Kunth., and Salvia farinacea Benth. `Rhea Blue', which are adapted to midsummer heat and low water, performed well with 0% to 25% ET0. Species considered to be heat or drought tolerant—Petunia ×hybrida hort. ex. E. Vilm. `Merlin White' and Glandularia J.F. Gmel. `Imagination'—required little or no irrigation. The bedding plant species evaluated in this study that required 25% or less ET0 are well adapted for low-water landscape installations.

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Yan Chen, Regina Bracy and Allen Owings

Annual vinca, Catharanthus roseus, is exceptionally adaptive to the summer heat and the sandy loam or clay soil in the southeastern region and provides season-long blooms once established in landscape plantings. A wide variety of colors, sizes, and applications are available for landscape use. However, diseases such as alternaria leaf spot and phytophthora leaf blight are prevalent in this region in vinca plantings. Effective disease control requires frequent fungicide application that is expensive and may pose negative effects on the environment. Proper planting techniques including date of planting, fertilization rate at planting, and variety selection may improve plant growth, reduce disease severity, and save landscape service business labor in disease management. Plants of three varieties: open-pollinated `Cooler Hot Rose', F1 hybrid `Titan Rose', and trailing variety `Mediterranean Lilac' were planted on 1 Apr. or 1 May in landscape plots. Plants were at the same growth stage at the time of planting and were fertilized with Osmocote 14–14–14 (3 months) at 0, 35, 70, or 140 g·m2. Plant growth index indicates that plant growth increased significantly at increasing fertilization rates; however, plant overall quality ratings were not significantly different among fertilized plants. Disease incidence in July suggests that late planting may reduce alternaria leaf spot in open-pollinated and hybrid upright type vinca. Disease severity in August was more pronounced on trailing vinca and more severe when plants were not fertilized or fertilized with the highest fertilization rate. Tissue analysis indicates that trailing vinca `Mediterranean Lilac' may require less fertilization than upright type.

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Carrie L. Whitcher, Matthew W. Kent and David Wm. Reed

The objective of this study was to quantify the optimum rates of water-soluble phosphorus (P) under constant nitrogen and potassium on the growth of new guinea impatiens (Impatiens hawkeri Bull.) `Paradise Violet' and vinca Catharanthus roseus `Pacifica Red' in soilless media in a recirculating subirrigation system. The experiment was designed so that only phosphate varied between treatments while all other nutrients remained constant. The ammoniacal N to nitrate N ratio was varied to counter balance increases in phosphate. Sodium was used as a counter ion to phosphate at higher concentrations of phosphate; sodium proved to be toxic at concentrations above 6 mm. In the new guinea impatiens experiment, there was a small increase in K due to the use of dibasic K phosphate to buffer pH. All growth parameters measured (height, leaf number, flower number, and shoot fresh and dry weight) showed significant differences with increasing P rate. Depending on the growth parameter measured, quadratic–linear models revealed an optimum P rate of 0.1 to 0.96 mm for new guinea impatiens `Paradise Violet' and 0.45 to 1.25 mm P for vinca `Pacifica Red'. For dry shoot weight, a common measure of optimum plant growth, the optimum P rate was 0.75 mm P for new guinea impatiens `Paradise Violet' and 0.67 mm P for vinca `Pacifica Red'. For flower number, a common measure of floral quality, the optimal P rate was 0.96 mm P for new guinea impatiens `Paradise Violet' and 1.25 mm P for vinca `Pacifica Red'. Electrical conductivity (EC) of the growing media increased significantly with increasing rate of P. At all rates, EC was significantly greater in the top layer than in the bottom and middle layers. The pH of the growing medium did not vary in relation to P concentration.

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Michael R. Evans, Bernard W. Krumpelman, Ramsey Sealy and Craig S. Rothrock

Vinca (Catharanthus roseus) is a common annual bedding plant species that is susceptible to root and stem rot caused by Phytophthora nicotianae. The experimental design was a 6×2×1 factorial with a total of 12 treatment combinations that had five replications and was repeated twice. Vinca seeds were planted in the middle nine plugs of a 5×5 five-milliliter round plug tray filled with sphagnum peat (control) or peat amended with 2.1 kg/m3 calcitic lime, 5.9 and 7.3 kg/m3 potassium silicate alone and combined with 3.0 kg/m3 calcium sulfate. A peat control drenched with metalaxyl after inoculation was also included. After germination, when the seedlings had one true leaf, half of the treatments were inoculated with 500 cfu of Phytophthora nicotianae per plug cell while the other half remained uninoculated. The percentage of germination for the potassium silicate combined with calcium sulfate (KSCS) (79% and 78%) was similar to the control (86%) and the metalaxyl treatment (83%), whereas the potassium silicate alone had poorer germination (69% and 71%) and plant growth. The percentage of mortality for the KSCS treatment (6% and 14%) was similar to the metalaxyl treatment (9%) but was significantly less than the control (100%). The average dry shoot and root weights for the KSCS treatments (4.4 and 4.9 mg; 2.7 and 2.2 mg) were similar to the metalaxyl treatment (5.0 and 3.6 mg) and the uninoculated control (5.0 and 3.2 mg), but were higher than the potassium silicate treatment alone (2.1 and 1.6 mg; 0.7 and 0.6 mg).

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James E. Altland, Charles H. Gilliam, James H. Edwards and Gary J. Keever

Selected fertilizer treatments were applied to vinca (Catharanthus roseus `Peppermint Cooler') in the landscape to determine their effect on growth and nutrient leaching. In plots 0.9 m × 2.3 m, inorganic fertilizers were applied as either a single application of 4.9 g N/m2 pre-plant, or a split application with 4.9 g N/m2 applied pre-plant followed by application of 2.45 g N/m2 at 8 and 12 weeks after planting (WAP). Inorganic fertilizers included 15N–0P–12.6K granular fertilizer, Osmocote 14N–6.0P–11.6K, and Osmocote 17N–3.0P–10.1K controlled-release fertilizers. Three different organically based fertilizers were applied pre-plant and were composed of recycled newspaper amended with animal manures (chicken, beef cattle, or dairy) and adjusted with (NH4)2SO4 to achieve C:N ratios of either 20:1 or 30:1. A standard industry treatment of 13N–5.6P–10.9K (4.9 g N/m2) incorporated pre-plant and 17N–3.0P–10.1K (4.9 g N/m2) topdressed post-plant was also included. Leachates, collected with lysimeters, from inorganic fertilizer plots had lower levels of total N (NO3 + NH4 +) compared to organically based fertilizer plots through 8 WAP. Of the inorganic fertilizer plots, those receiving 15N–0P–12.6K granular fertilizer had higher total N levels at 1, 2, and 4 WAP than other inorganic fertilizer plots. Total N in leachates declined over the study and by 12 WAP were similar among all treatments. Vinca treated with organically based fertilizers (C:N 20:1) had the highest foliar color ratings through 8 WAP; however, color ratings declined thereafter and by 16 WAP had the lowest ratings. Plants treated with organically based fertilizers had greater shoot dry weights 20 WAP and larger growth indices 8 and 20 WAP.

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Trisha Blessington Haley and David Wm. Reed

Two experiments were conducted to investigate the effect of K fertilizer rates on growth of New Guinea impatiens (Impatiens Hawkeri Bull.), vinca (Catharanthus roseus (L.) G. Don) and petunia (Petunia ×hybrida Hort. Vilm.-Andr.) in a recirculating subirrigation system. Based on a variety of growth parameters, a broad range of K concentrations allowed maximum growth, notably 1 to 6 mM for New Guinea impatiens `Ovation Salmon Pink Swirl', 2 mm for New Guinea impatiens `Cameo' and `Illusion', 2 to 8 mm for vinca `Pacifica Apricot', and 2 to 16 mm for petunia `Trailing Wave Misty Lilac'. Thus, the lowest concentration that allowed maximum growth was 1 to 2 mm K. A third experiment compared the optimum K concentration and K balance of vinca grown with recirculating subirrigation versus top-watering. Based on a variety of growth parameters of vinca `Pacifica Red', the lowest concentration that allowed maximum growth was 2 mm K with recirculating subirrigation and 4 mm K with top-watering. The K balance demonstrated that subirrigated plants were twice as efficient in K use compared to the top-watered plants. Leachate loss was the major contributor to inefficiency in top-watered plants. Electrical conductivity (EC) of the growing medium remained below the recommended level of 1.2 dS·m-1 in both irrigation methods at K concentrations of 16 mm and below in the bottom layer and 8 mm and below in the middle layer. In the top layer of the growing medium, EC was above the recommended level at all K concentrations tested in subirrigation at all concentrations, and in top-watering at 16 mm and above.

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Holly L. Scoggins, Douglas A. Bailey and Paul V. Nelson

There is a need for a substrate testing method suited for plug plant production. Methods currently used by most growers and analytical labs include the saturated media extract (SME) and the 2 water: 1 substrate (v/v) suspension. These methods are not particularly well-adapted to plug production. The press extraction (PE) method has been developed as a simple and quick alternative to these methods. However, interpretive standards for chemical analysis of plug substrates do not exist for PE. This study was designed to provide the necessary correlations between these methods to allow for development of pH, electrical conductivity (EC), and nutrient interpretive ranges for plugs. Plugs of begonia (Begonia ×semperflorens-hybrida Hort.), impatiens (Impatiens walleriana Hook. f.), marigold (Tagetes erecta L.), petunia (Petunia ×hybrida Hort. Vilm.-Andr.), salvia (Salvia splendens F. Sellow ex Roem. & Schult.), and vinca (Catharanthus roseus L.) were collected from commercial greenhouses and the substrate solution extracted with the PE, SME, and 1:2 methods. Plugs of begonia, celosia (Celosia argentea L. var. cristata (L.) Kuntze Plumosa Group), marigold, petunia, and vinca were grown with three fertilizer rates of 50, 150, and 250 mg·L-1 N. Shoots were harvested 30 days after planting and the solution was extracted from each flat using the three methods. For both experiments, PE EC was equal to or higher than the SME EC, and the pH was equal to or lower than the SME pH. The pH from the 1:2 was also similar to the PE. However, 1:2 EC results were consistently the lowest because of the dilution inherent in the 1:2 method. Interpretation ranges for pH and EC relationships were calculated to compare results from the PE with published sufficiency ranges for the SME and 1:2.

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James E. Faust, Veronda Holcombe, Nihal C. Rajapakse and Desmond R. Layne

Daily light integral (DLI) describes the rate at which photosynthetically active radiation is delivered over a 24-hour period and is a useful measurement for describing the greenhouse light environment. A study was conducted to quantify the growth and flowering responses of bedding plants to DLI. Eight bedding plant species [ageratum (Ageratum houstonianum L.), begonia (Begonia ×semperflorens-cultorum L.), impatiens (Impatiens wallerana L.), marigold (Tagetes erecta L.), petunia (Petunia ×hybrida Juss.), salvia (Salvia coccinea L.), vinca (Catharanthus roseus L.), and zinnia (Zinnia elegans L.)] were grown outdoors in direct solar radiation or under one of three shade cloths (50, 70 or 90% photosynthetic photon flux (PPF) reduction) that provided DLI treatments ranging from 5 to 43 mol·m–2·d–1. The total plant dry mass increased for all species, except begonia and impatiens, as DLI increased from 5 to 43 mol·m–2·d–1. Total plant dry mass of begonia and impatiens increased as DLI increased from 5 to 19 mol·m–2·d–1. Impatiens, begonia, salvia, ageratum, petunia, vinca, zinnia, and marigold achieved 50% of their maximum flower dry mass at 7, 8, 12, 14, 19, 20, 22, and 23 mol·m–2·d–1, respectively. The highest flower number for petunia, salvia, vinca, and zinnia occurred at 43 mol·m–2·d–1. Time to flower decreased for all species, except begonia and impatiens, as DLI increased to 19 or 43 mol·m–2·d–1. There was no consistent plant height response to DLI across species, although the shoot and flower dry mass per unit height increased for all species as DLI increased from 5 to 43 mol·m–2·d–1. Guidelines for managing DLI for bedding plant production in greenhouses are discussed.