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Robert Berghage

Temperature management has emerged as an important tool for plant height control in greenhouse production systems. This is particularly important in vegetable transplant production where chemical controls for plant height are limited or not legal. Plant height is a function of the number of nodes and the length of each internode, and both are strongly influenced by greenhouse temperatures. Node number, or formation rate, is primarily a function of the average greenhouse temperature, increasing as the average temperature increases. Internode length is strongly influenced by the relationship between the day and night temperature, commonly referred to as DIF (day temperature - night temperature). As DIF increases, so does internode length in most plant species studied. Although the nature and magnitude of temperature effects vary with species, cultivar, and environmental conditions, these two basic responses can be used to modify transplant growth. Although data are limited, controlling transplant height with temperature does not appear to adversely influence plant establishment or subsequent yield.

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Robert T. Eddy and Phillip J. Belfiore

Many studies have described the ability of individuals with mental disabilities to learn vocational tasks commonly performed in greenhouses, and a survey of horticulture employers reports a favorable perception toward the work habits of these individuals. Productivity data are not available from these studies, however. We sought to quantify productivity of individuals with and without mental disabilities performing entry-level greenhouse tasks. Information on ten tasks was compiled from surveys of four vocational centers with greenhouse production and six commercial greenhouses. Individuals with mental disabilities produced at rates of 46% to 192% of corresponding commercial rates, with seven often skills performed. above 75% of the commercial rate. The results from this pilot study suggest that individuals with mental disabilities can achieve satisfactory productivity in real work settings. While significance was not achieved due to limitations of the study, the results provide a baseline for further study by other researchers. The practical significance of these findings can be judged by trainers and employers.

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Jessica Phillips, James M. Garner, and Allan M. Armitage

Five taxa of Helichrysum Mill. and Brachycome Cass. were recently evaluated for greenhouse production and amenity use. Preliminary studies on the influence of photoperiod, temperature, and growth regulators were conducted for H. bracteatum Vent., (syn Bracteantha bracteata) `Sunray' and `Matilda Yellow', H. apiculatum D.C, (syn Chrysocephalum apiculatum) `Golden Buttons' and Brachycome iberidifolia Benth. `Jumbo Mauve' and `Mauve Delight'. All taxa of Helichrysum were quantitative LD plants, flowering slightly more rapidly under night-break (2200-0200 HR) and extended day incandescent lighting, compared with 9-h short-day treatment. No influence of photoperiod occurred with cultivars of Brachycome. Constant temperature of 12, 20, or 28 °C were provided and all taxa demonstrated a linear decrease in flowering time as temperatures increased. The growth index (average of height and two measurements of width) was also influenced by temperature. Paclobutrazol and daminozide were applied at different concentrations and frequencies. Paclobutrazol was more effective than daminozide in both genera, and daminozide was ineffective in Brachycome.

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M.D. Orzolek

Hydrophylic polymers are synthetic, water-absorbing monomers of high molecular weight. They have been used as absorbents in the diaper industry for the past 30 years. Polymers differ from each other in the specific monomer building block, amount of water absorbed per gram of material, particle size and distribution, response to salinity, and cost. While there are only four different monomers used in the production of polymers, there are several dozen polymers available commercially under different trade names. Benefits derived from polymer application to soil or artificial medium include: increase in water-holding capacity, increase in pore size/number, increase in soil nutrient reserves, and reduction in soil compaction. Initial use of polymers was reported in greenhouse production in the late 1970s, but is now used in the production of fruits, vegetables, and turf. Development of application equipment has the potential to expand the use of polymers to large commercial growers.

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L-Y. Li and J.H. Lieth

Greenhouse crop production involves high rates of energy input to implement a greenhouse microclimate that results in high productivity levels, correct crop timing, and desired product specifications. Producing quality crops while maintaining low energy consumption is achievable through improved crop management and environment control strategies. In this study, greenhouse crops and their microclimate were treated as an integrated system that was driven by solar radiation and external energy input. A set of simulation models were developed to describe the greenhouse climate, the crop, and their dynamic interactions. The temperature and light regimes were simulated using the greenhouse energy budget under typical weather patterns. The crop model simulated growth and development of several ornamental greenhouse crops. Coupling the crop model with the greenhouse energy model resulted in a system that allows determination of optimal strategies for crop management and environmental control. This greenhouse/crop system can be used to assist growers with formulating strategies of greenhouse production management.

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Daniel F. Warnock

Greenhouse production of rosemary (Rosemarinus officinalis) as small potted Christmas-tree topiaries for holiday sales have become necessary for many companies marketing to large retail outlets. Topiaries must be sheared multiple times to obtain an acceptable Christmas-tree shape. Most production greenhouses use hand pruning shears or hand-held cordless grass shears to shape topiaries free hand or with the aid of a template. Crop size and uniformity can vary with these shearing methods. To create a more uniform rosemary Christmastree topiary for cultivar evaluations, a mechanical shearing device constructed from over-the-counter parts was developed at the University of Illinois. A detailed description of the design and construction of this mechanical shearing device is presented in this report.

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C. Elizabeth Succop and Steven E. Newman

During 1995, 33 poinsettia cultivars were evaluated for Colorado greenhouse production conditions. Plants were supplied by the Paul Ecke Poinsettia Ranch, Fischer Geraniums USA, Oglevee, and Mikkelsens. At the end of the production period, Colorado greenhouse growers were invited to an open house and asked to judge the cultivars for plant, bract, and cyathia quality. As rated by the 24 growers, the best red cultivars in overall performance were `Freedom Red', `Nutcracker Red', `Cortez', and `Bonita', respectively. The best pink cultivars in overall performance were `Nutcracker Pink', `Maren', and `Flirt', respectively. The best white cultivars in overall performance were `Nutcracker White' and `V-17 Angelika White', respectively. The best novelty cultivars in overall performance were `Puebla' and `Monet', respectively.

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Edward F. Durner, E. Barclay Poling, and John L. Maas

Plugs are rapidly replacing fresh-dug bare-root and cold-stored frigo plants as transplants for strawberry (Fragaria × ananassa) production worldwide. Plugs have many advantages over these other types of propagules. They are grown in controlled environments (greenhouses, tunnels) in less time than field produced bare-root transplants, and are not exposed to soilborne pathogens. Plugs afford greater grower control of transplanting dates, provide mechanical transplanting opportunities and allow improved water management for transplant establishment relative to fresh bare-root plants. New uses for plugs have been identified in recent years; for example, photoperiod and temperature conditioned plugs flower and fruit earlier than traditional transplants and plugs have been used for programmed greenhouse production. Tray plants have superior cold storage characteristics relative to bare-root, waiting-bed transplants. Both fresh and frozen plugs are used in a number of indoor and outdoor growing conditions and cultural systems.

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Shannon E. Beach*, Terri W. Starman, and H. Brent Pemberton

Bracteantha bracteata (Vent.) Anderb. & Haegi (bracteantha) is a vegetative annual produced as a 12.7-cm potted plant in 6 weeks of greenhouse production. A dense leaf canopy produced with a conventional constant-feed fertilization regime (300 mg·L-1 20N-4.4P-16.6K) caused increased disease pressure and lower leaf chlorosis during greenhouse production. During shelf life, lower leaves of plants con-tinued to become chlorotic. The objective was to decrease leaf area and prevent lower leaf chlorosis without affecting harvest time, plant quality or shelf life of two cultivars of three series of bracteantha. The first experiment was to reduce the rate of fertilizer two weeks prior to harvest. Treatments were no fertility reduction (300 mg/liter), 50% reduction (150 mg/liter), and 100% reduction (0 mg·L-1). At harvest, plants were evaluated for shelf life in a growth room at 21.1 ± 1.3 °C and 6 μmol·m-2·s-1 PPF. Five cultivars in the 100% fertility reduction treatment had decreased height and/or width index at harvest and three cultivars maintained higher postharvest quality ratings compared to the other treatments. Separately, the effect of the duration of fertilization was evaluated by terminating fertilization at weekly intervals (0-6 weeks) throughout production. Ceasing fertilization two to three weeks prior to harvest produced plants with lower leaf area without affecting flower number. In another experiment, thidiazuron (TDZ) as a foliar spray at 0, 0.1, 0.5, and 1.0 mg·L-1 was applied to decrease lower leaf yellowing. SPAD-502 chlorophyll meter readings of lower leaves were increased with 0.1 mg·L-1 TDZ treatment compared to the control. Phytotoxic symptoms occurred on plants receiving higher TDZ rates.

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Nihal C. Rajapakse and John W. Kelly

Transpiration rates of chrysanthemum [Dendranthema ×grandiflorum (Ramat.) Kitamura] plants grown under spectral filters were evaluated as part of an investigation on using light quality to regulate plant growth. The 6% CuSO4·5H2O spectral filter reduced photosynthetic photon flux density in red (R) and far red (FR) wavelengths and increased the R: FR and blue (B): R ratios (B = 400 to 500 nm; R = 600 to 700 nm; FR = 700 to 800 nm) of transmitted light relative to the water (control) filter. After 28 days, cumulative water use of plants grown under CuSO4 filters was ≈37% less than that of control plants. Transpiration rates were similar among plants grown under CuSO4 and control filters when expressed as leaf area, a result suggesting that the reduced cumulative water loss was a result of smaller plant size. Plants grown under CuSO4 filters had slightly lower (10%) stomatal density than control plants. Light transmitted through CuSO4 filters did not alter the size of individual stomata; however, total number of stomata and total stomatal pore area per plant was ≈50% less in plants grown under CuSO4 filters than in those grown under control filters due to less leaf area. The results suggest that altering light quality may help reduce water use and fertilizer demands while controlling growth during greenhouse production.