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Paul A. Thomas and Joyce G. Latimer

Perennial growers experience marketing difficulty when the stem length, or height of their perennial stock is excessive. Both wholesale and retail outlets desire to keep height to a minimum, while still promoting the production of flowers. The objective of this study was to screen containerized, spring-planted perennials for response to the growth retardants Sumagic, Bonzi, and B-Nine. Each perennial variety used was treated with B-Nine (Daminozide at 5000 ppm Bonzi (paclobutrazol) at 240 ppm, and Sumagic (uniconizole-P) at the following rates: 0, 40, 80, 120, and 160 ppm.Pre-cooled plugs of cultivars were selected from the genera Achillea, Coreopsis, Echinaceae, Digitalis, Gaillardia, Phlox, Rudbeckia, Alcea, Veronica, and Monarda. A randomized complete block design was implemented. Eight of the nine cultivars were responsive to Sumagic, with a 12% to 79% range of reduction in height. Seven cultivars were responsive to Bonzi with a 20% to 61% range of reduction. Only one cultivar was responsive to B-Nine, requiring two applications of 5000 ppm, to yield a 22% reduction in height at 4WAT. Based upon growers' desire for up to 50% height reduction, a 30% height reduction assessment point was established as a minimum rate for production, and a 50% to 60% reduction was established as the maximum landscape rate (based upon in-landscape persistence).

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Paul A. Thomas and Joyce G. Latimer

Annual vinca [Catharanthus roseus (L.) G. Don] is intolerant of high fertility, cool temperatures, and wet soil conditions, making vinca difficult for growers to produce alongside other, more tolerant bedding plants. Our objective was to develop better recommendations for producers. Growth of `Grape Cooler' vinca was compared using different production inputs, including type of media (with or without bark), form of micronutrient source, and form of N. Optimal root and shoot dry weights occurred in peat-lite media with either sulfated or chelated micronutrients adjusted to pH 5.5. Root and shoot dry weights were greatest when high nitrate-N to ammonium-N ratio fertilizers were used. Root and shoot dry weights were negatively affected by high levels of ammonium-N in the fertilizer solution. Root development is the critical factor in the production of high-quality vinca. Our data suggest that root development may be optimized by using fertilizer products that have a high nitrate to ammoniacal nitrogen ratio. Micronutrients in the sulfate form also seem to enhance growth when medium pH is maintained near 5.5. Use of high-porosity, peat-based mixes appears to provide an optimal root growth environment.

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Joyce G. Latimer and Paul A. Thomas

Nine perennial bedding plants were screened for responsiveness to the plant growth retardant, Sumagic (uniconazole-P). Two weeks after planting, plugs were treated with one foliar spray of Sumagic at 0, 40, 80, 120, or 160 ppm at the label-recommended volume. Plant growth of Gaillardia grandiflora `Goblin' was not reduced by Sumagic. Height of Achillea × `Moonshine' was reduced 8% to 12% at 4 weeks after treatment (WAT), and the reduction persisted through 8 weeks after planting (WAP) to the landscape. Phlox paniculata `Joliet' responded linearly to increasing Sumagic rate with a maximum height reduction of 32% at 160 ppm. Coreopsis grandiflora `Sunray', Rudbeckia fulgida var. Sullivantii `Goldsturm' and Monarda didyma `Blue Stocking' responded significantly to Sumagic with 30% to 60% height reductions at 4 WAT, but no persistent effects at 8 WAP. Height of Veronica alpine `Goodness Grows' was reduced 32% to 68% at 4 WAT, but all Sumagic rates resulted in persistent reductions in plant height at 12 WAP. Plant height of Alcea rosea mix and Echinacea purpurea were excessively reduced (up to 79%) at 4 WAT, but there were no persistent effects on height of Alcea in the landscape. All rates of Sumagic resulted in persistent reductions in height of Echinacea at 8 WAP, but only plants treated with 120 and 160 ppm Sumagic were still significantly shorter than controls at 12 WAP

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Joyce G. Latimer and Paul A. Thomas

Brushing 2-week-old `Sunny' tomato (Lycopersicon esculentum Mill.) seedlings, grown in a commercial production greenhouse, for a period of 5 weeks reduced transplant growth and improved plant appearance. Brushing reduced stem length 37% and leaf area 31% relative to nontreated control plants. Plants were darker green in color, stockier, easier to handle, and tougher (exhibited less breakage) than nontreated plants.

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Teresa M. Hood, Harry A. Mills, and Paul A. Thomas

Nutrient uptake by `Apache', `Jersey City', `Peoria', and `Philadelphia' snapdragons (Antirrhinum majus L.) was compared at three developmental stages: Stage I, vegetative to bud initiation; Stage II, bud initiation to visible bud; and Stage III, visible bud to anthesis. Significant differences in uptake occurred between one or more developmental stages for all nutrients tested: \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\mathrm{-}\mathrm{N},\mathrm{NH}_{4}^{+}\mathrm{-}\mathrm{NB}\) \end{document}, B, Ca, Cu, Fe, K, Mg, Mn, Mo, P, and Zn. Uptake of most of the nutrients increased or remained high during Stage III. These results indicate that the current cultural practice of stopping fertilization at bud elongation should be reexamined. Differences in uptake between cultivars were found only for \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\mathrm{-}\mathrm{N}\) \end{document}, as uptake by `Apache' was significantly higher than uptake by `Philadelphia'.

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Joyce G. Latimer, Ronald D. Oetting, and Paul A. Thomas

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Peter Alem, Paul A. Thomas, and Marc W. van Iersel

Rising concerns over environmental impacts of excessive water and fertilizer use in the horticultural industry necessitate more efficient use of water and nutrients. Both substrate volumetric water content (θ) and fertilizer affect plant growth, but their interactive effect is poorly understood. The objective of this study was to determine the optimal fertilizer rates for petunia (Petunia ×hybrida) ‘Dreams White’ grown at different θ levels. Petunia seedlings were grown at four levels of θ (0.10, 0.20, 0.30, and 0.40 m3·m−3) with eight different rates of controlled-release fertilizer (CRF) (Osmocote 14-14-14; 14N–6.1P–11.6K; rates of 0 to 2.5 g/plant, equivalent to 0 to 6.25 kg·m−3 substrate). Shoot dry weight increased as the CRF rate increased from 0 to 1.67 g/plant but decreased again at even higher CRF rates. The effect of CRF rate on growth was more pronounced at higher θ. Leaf size doubled as the θ thresholds increased from 0.10 to 0.40 m3·m−3. Flowering was reduced by a combination of high CRF rates (greater than 0.63 g/plant) and high θ (0.30 and 0.40 m3·m−3), indicating that optimal conditions for vegetative growth are different from those for maximal flowering. These results suggest that without leaching, high-quality petunias can be grown with lower CRF rates than commercially recommended rates.

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Stephanie E. Burnett, Marc W. van Iersel, and Paul A. Thomas

French marigold (Tagetes patula L. `Boy Orange') was grown in a peat-based growing medium containing different rates (0, 15, 20, 30, 42, or 50 g·L–1) of polyethylene glycol 8000 (PEG-8000) to determine if PEG-8000 would reduce seedling height. Only 28% to 55% of seedlings treated with 62, 72, or 83 g·L–1 of PEG-8000 survived, and these treatments would be commercially unacceptable. Marigolds treated with the remaining concentrations of PEG-8000 had shorter hypocotyls, and were up to 38% shorter than nontreated controls at harvest. Marigold cotyledon water (ψw), osmotic (ψs), and turgor (ψp) potentials were significantly reduced by PEG-8000, and ψp was close to zero for all PEG-treated seedlings 18 days after seeding. Whole-plant net photosynthesis, whole-plant dark respiration, and net photosynthesis/leaf area ratios were reduced by PEG-8000, while specific respiration of seedlings treated with PEG-8000 increased. Marigolds treated with concentrations greater than 30 g·L–1 of PEG-8000 had net photosynthesis rates that were close to zero. Fourteen days after transplanting, PEG-treated marigolds were still shorter than nontreated seedlings and they flowered up to 5 days later. Concentrations of PEG from 15 to 30 g·L–1 reduced elongation of marigold seedlings without negatively affecting germination, survival, or plant quality. It appears that marigold seedlings were shorter because of reduced leaf ψp and reductions in net photosynthesis.