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Steven E. Newman and Jeffrey S. Tant

An experiment was conducted to determine the influence of eight commercial root-zone media (four peat based and four pine bark based) on the effects of paclobutrazol applied to Euphorbia pulcherrima Willd. `Eckespoint Celebrate 2' as an impregnated spike or a drench. Paclobutrazol treatments had the least influence on stem elongation of poinsettias grown in the peat-based medium containing Bacctite, a compressed peat product designed to increase aeration and cation exchange capacity, or composted pine bark ground to a particle size that could pass through an opening 1 cm or smaller. Spikes were more effective at reducing shoot elongation than drenches. Spike treatments also resulted in lower bract dry-matter accumulation than drenches. Paclobutrazol applied as a spike to poinsettias at pinch could combine pinching and chemical growth regulator application into one simultaneous operation. Chemical name used: (±)-(R*,R*)-beta-[(4-chlorophenyl)methyl]-alpha-(1, 1,-dimethyl)-1H-1,2,4,-triazole-1-ethanol (paclobutrazol).

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Christopher J. Currey, Kellie J. Walters, and Kenneth G. McCabe

Our objective was to quantify the efficacy of different plant growth regulator (PGR) substrate drenches on growth of lantana (Lantana camara) cultivars varying in growth habit. Rooted ‘Little Lucky Peach Glow’, ‘Lucky Peach’, and ‘Landmark Peach Sunrise’ lantana cuttings were individually planted into 4-inch-diameter containers filled with a commercial, soilless growing substrate. Fourteen days after planting, solutions containing 0 (control), 0.5, 1, 2, or 4 mg·L−1 ancymidol, flurprimidol, paclobutrazol, or uniconazole were applied to the surface of the growing substrate. Six weeks after applying PGR drenches, data were collected. The growth index (GI), an integrated measurement of plant size incorporating the height and widths of plants, was calculated. There was variation in the GI among the control plants, reflecting variation among cultivars within the species. In addition, we measured variation in activity among the different PGRs applied. Across the concentrations applied, ancymidol generally had the lowest activity across the four PGRs. For example, drenches containing 4 mg·L−1 ancymidol resulted in plants that were similar to plants treated with 0.5 to 1 mg·L−1 flurprimidol or uniconazole or 2 mg·L−1 paclobutrazol for ‘Lucky Peach’ lantana. Across all cultivars, flurprimidol and uniconazole had the greatest activity in suppressing plant height, width, and GI. Substrate drenches containing flurprimidol, paclobutrazol, or uniconazole are useful to control size of lantana produced in containers, though the recommended concentration depends on the active ingredient and the growth habit of cultivars being treated.

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W. Garrett Owen

The objective of this study was to determine optimum fertilizer concentrations, identify leaf tissue nutrient sufficiency ranges by chronological age, and establish leaf tissue nutrient standards of containerized Russian sage (Perovskia sp.). Common Russian sage (P. atriplicifolia Benth.) and ‘Crazy Blue’ Russian sage were greenhouse-grown in a soilless substrate under one of six constant liquid fertilizer concentrations [50, 75, 100, 200, 300, or 400 mg·L−1 nitrogen (N)] with a constant level of a water-soluble micronutrient blend. Fertilizer concentrations sufficient for optimal plant growth and development were determined by analyzing plant height, diameter, growth index, primary shoot caliper, axillary shoot number, and total dry mass; they were found to be 100 to 200 mg·L−1 N after a 6-week crop cycle. Recently, mature leaf tissue samples were collected from plants fertilized with 100 to 200 mg·L−1 N and analyzed for elemental contents of 11 nutrients at 2, 4, and 6 weeks after transplant (WAT). An overall trend of increasing foliar nutrient concentrations over time was observed for all elemental nutrients. For instance, at 2 WAT, the total N concentrations of common Russian sage and ‘Crazy Blue’ Russian sage ranged between 3.68% and 5.10% and between 3.92% and 5.12%, respectively, and increased to ranges of 5.94% to 5.98% and 5.20% to 5.86% at 6 WAT, respectively. Before this study, no leaf tissue concentration standards have been reported; therefore, this study established leaf tissue concentration sufficiency ranges for the trialed Perovskia selections.

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Brigitte D. Crawford, John M. Dole, and Ben A. Bergmann

Influence of season of the year, cutting week within a propagation cycle (number of weeks from which a stock plant has been harvested), stock plant age, and rooting compound on postpropagation cutting quality, and adventitious rooting was examined for ‘Stained Glass’ coleus (Solenostemon scutellarioides). Cuttings were of higher quality and produced more robust root systems when a propagation cycle started in summer vs. fall or spring even when cuttings were harvested from stock plants of the same age. Cutting week within a propagation cycle significantly influenced postpropagation cutting quality and rooting when cuttings were harvested over many weeks from the same stock plants and when cuttings were harvested for three propagation events using stock plants of different ages. When cuttings were harvested on the same days from stock plants of three distinct ages, cuttings harvested in the first week were larger with greater root weights but had more yellowed leaves and lower quality ratings compared with the two subsequent cutting weeks, but stock plant age had no effect on any observed parameter. Treatment with rooting compound did not overcome the significant influences of season and cutting week within a propagation cycle whether rooting was carried out in a greenhouse or growth chamber. Shoot and root fresh and dry weights were positively correlated with both daylength and midday instantaneous light of the stock plant environment.

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W. Garrett Owen

Calceolaria (Calceolaria ×herbeohybrida) is a flowering potted greenhouse crop that often develops upper-leaf chlorosis, interveinal chlorosis, and marginal and leaf-tip necrosis (death) caused by cultural practices. The objectives of this research were to 1) determine the optimal incorporation rate of dolomitic and/or hydrated lime to increase substrate pH; 2) determine the influence of the liming material on substrate pH, plant growth, and leaf tissue nutrient concentrations; and 3) determine the optimal substrate pH to grow and maintain during calceolaria production. Sphagnum peatmoss was amended with 20% (by volume) perlite and incorporated with pulverized dolomitic carbonate limestone (DL) and/or hydrated limestone (HL) at the following concentrations: 48.1 kg·m−3 or 144.2 kg·m−3 DL, 17.6 kg·m−3 DL + 5.3 kg·m−3 HL, or 17.6 kg·m−3 DL + 10.6 kg·m−3 HL to achieve a target substrate pH of 4.5, 5.5, 6.5, and 7.5, respectively. Calceolaria ‘Orange’, ‘Orange Red Eye’, ‘Yellow’, and ‘Yellow Red Eye’ were grown in each of the prepared substrates. For all cultivars, substrate solution pH increased as limestone incorporation concentration and weeks after transplant (WAT) increased, although to different magnitudes. For example, as limestone incorporation increased from 48.1 kg·m−3 DL to 17.6 kg·m−3 DL + 10.6 kg·m−3 HL, substrate solution pH for ‘Orange’ calceolaria increased from 4.1 to 6.9 to 4.8 to 7.2 at 2 and 6 WAT, respectively. Substrate solution electrical conductivity (EC) and growth indices were not influenced by limestone incorporation, but total plant dry mass increased. Few macronutrients and most micronutrients were influenced by limestone incorporation. Leaf tissue iron concentrations for ‘Orange’, ‘Orange Red Eye’, ‘Yellow’, and ‘Yellow Red Eye’ calceolaria decreased by 146%, 91%, 71%, and 84%, respectively, when plants were grown in substrates incorporated with increasing limestone concentrations from 144.2 kg·m−3 DL to 17.6 kg·m−3 DL + 10.6 kg·m−3 HL (pH 6.5–6.9). Therefore, incorporating 144.2 kg·m−3 DL into peat-based substrates and maintaining a pH <6.5 will avoid high pH–induced Fe deficiency and prevent upper-leaf and interveinal chlorosis.

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Raymond A. Cloyd and Clifford S. Sadof

A 2-year greenhouse study was conducted to evaluate the seasonal population dynamics and use of an action threshold for western fl ower thrips (Frankliniella occidentalis) in cut carnation (Dianthus caryophyllus). An action threshold of 20 thrips/card/week was adopted to time insecticide applications. The highest numbers of thrips were caught on blue-colored sticky cards from May through September whereas the lowest thrips numbers were present from November through March 1994 and 1995. Thrips numbers based on sticky card counts, from December through March for both years were below the action threshold and as a result, no insecticides were applied. Thrips abundance on blue sticky cards was significantly correlated with both numbers of thrips in fl owers and a subjective ranking of fl ower quality. Seasonal patterns of both insecticide use and numbers of damaged fl ow- ers closely followed patterns of thrips abundance found on blue sticky cards. Our findings are the first to demonstrate, based on a case study over a 2-year period, that routinely scouting for thrips throughout the year can lead to fewer insecticide applications and thus possible cost savings in labor and insecticide purchases. This study suggests that sticky cards can be an effective tool for reducing insecticide applications in regions of the U.S. where there are seasonal fl uctuations of thrips abundance.

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Hye-Ji Kim and Xinxin Li

This study was undertaken to critically analyze the effects of reduced phosphorus (P) on shoot and root growth, partitioning, and phosphorus utilization efficiency (PUtE) in lantana (Lantana camara ‘New Gold’). Plants were grown in a 1:1 mixture of perlite and vermiculite with complete nutrient solutions containing a range of P concentrations considered to be deficient (1 mg·L−1), low (3 and 5 mg·L−1), adequate (10 mg·L−1), and high (20 and 30 mg·L−1). Higher P supply had most dramatic effect on increasing the number of leaves and leaf surface area, subsequently leading to a disproportionate increase in shoot biomass than root biomass. Increasing P from 1 to 30 mg·L−1 linearly (P < 0.0001) increased shoot dry weight (DW) during vegetative growth, and logarithmically (P < 0.0001) during reproductive growth. Regardless of plant growth stage, biomass of roots and flowers (inflorescences) logarithmically increased (P < 0.0001) with increasing P concentrations. Plants grown with lower P allocated more biomass to roots than shoots, resulting in a higher root-to-shoot ratio. Increasing P concentration to 20 mg·L−1 increased the accumulation of P in all plant parts, but predominantly in shoots, whereas further increasing the concentration increased the accumulation primarily in roots and flowers. Higher P accumulation in plant tissues did not strongly contribute to the biomass production. Phosphorus utilization efficiency was higher with lower P supply in all plant tissues. P-deficient roots had the highest PUtE and specific root length (SRL), and retained higher proportion of P compared with nondeficient roots. Our results indicate that P concentration at 20 mg·L−1 is sufficient to maintain optimal vegetative growth while reproductive growth does not require P concentrations over 10 mg·L−1 as it stimulates greater level of P accumulation in plant parts with little or no effect on growth and flowering, and biomass accumulation in lantana.

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Julián Miralles-Crespo and Marc W. van Iersel

Irrigation control systems that irrigate container-grown plants based on crop water needs can reduce water and fertilizer use and increase the sustainability of ornamental crop production. The use of soil moisture sensors to determine when to irrigate is a viable option. We tested a commercially available irrigation controller (CS3500; Acclima, Meridian, ID), which uses time domain transmissometry (TDT) sensors to measure soil volumetric water content (θ). The objectives of this study were: 1) to test the accuracy of TDT sensors in soilless substrate; 2) to quantify the ability of the Acclima CS3500 irrigation controller to maintain stable θ readings during the production of container-grown begonia (Begonia semperflorens L.) by turning a drip irrigation system on and off as needed; and 3) to study the growth and photosynthetic physiology of begonia at six θ levels. Calibration of the TDT sensors in pots filled with substrate (but without plants) showed that the θ determined by the TDT sensors had a very close relationship (R 2 = 0.99) with the gravimetrically determined θ, but the TDT sensors underestimated θ by ≈0.08 m3·m−3. Therefore, a custom calibration of the TDT sensors for the soilless substrate was necessary to get accurate θ data. The irrigation controller was programmed to maintain six θ thresholds, ranging from 0.136 to 0.472 m3·m−3 (based on our own sensor calibration), and was able to maintain θ readings within 0.008 m3·m−3 of the threshold. Theta and Sigma probes were used to collect comparative θ and bulk electrical conductivity (EC) data, respectively. The results showed a strong correlation with TDT sensor measurements of θ (R 2 = 0.92) but a moderate relationship for bulk EC (R 2 = 0.53). The begonias had similar dry weight at θ levels of 0.348 m3·m−3 and higher, whereas total evapotranspiration increased linearly with the θ threshold. The lowest θ threshold reduced leaf size, net photosynthesis (Pn), and stomatal conductance (g S). Overall, the TDT sensors can provide accurate measurements of θ in soilless substrate but need substrate-specific calibration. The Acclima CS3500 controller, using TDT sensors, was able to maintain stable θ readings throughout a production cycle. These results suggest that this irrigation controller may be suitable for production of greenhouse crops as well as in drought stress research.

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Alison Bingham Jacobson, Terri W. Starman, and Leonardo Lombardini

before they are watered. Either watering regimen is detrimental to plant health and hastens their decline in postharvest quality and shelf life at the retail level. Hardening off, or toning, at the end of the greenhouse production cycle by reducing

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D. Scott NeSmith and John R. Duval

Transplants for both vegetable and floral crops are produced in a number of various sized containers or cells. Varying container size alters the rooting volume of the plants, which can greatly affect plant growth. Container size is important to transplant producers as they seek to optimize production space. Transplant consumers are interested in container size as it relates to optimum post-transplant performance. The following is a comprehensive review of literature on container size, root restriction, and plant growth, along with suggestions for future research and concern.