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  • Author or Editor: Youbin Zheng x
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To evaluate the performance of four newly developed high-intensity-discharge lamp types on plant growth and production, tomato (Lycopersicon esculentum cv. Tradiro F1) plants were grown indoors under 100% artificial lighting for 17 weeks. The four lamp types were: high-pressure sodium high output [HPS(HO)], high-pressure sodium standard [HPS(STD)], metal halide warm deluxe [MH(WDX)] and metal halide cool deluxe [MH(CDX)]. All the lamps tested were 1000 W. HPS(HO) had the highest electrical energy use efficiency (EUE) (0.98 μmol·m–2·s–1·W–1 at 40 cm directly under the lamp); HPS(STD), MH(WDX) and MH(CDX) had 93%, 72% and 61% of the EUE of the HPS(HO), respectively. The photosynthetically active radiation (PAR) outputs of different lamp types had the following order: HPS(HO) > HPS(STD) > MH(WDX) > MH(CDX). The percentage red of PAR of the four tested lamp types had the same order as above, but the percentage blue of PAR of these lamp types had exactly the opposite order. As a result, plants growing under the two HPS lamp types were taller and flowered and fruited earlier than plants under the two MH lamp types. Chlorophyll content index was generally greater in leaves under MH lamps than in leaves under HPS lamps. We recommend that the HPS lamp be used for flowering and fruiting crops and the MH lamp would be better used for foliar and compact crops.

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To select plant species and species combinations for northern climates, mats with different plant species and species combinations were constructed on a green roof plant production farm and later transported and installed on an urban rooftop. There were three treatments: two different planting combinations, which together consisted of 10 diverse plant species [both stonecrop (Sedum) species and nonstonecrop species], and a control, which consisted of 26 stonecrop species used for standard mat production. Growth measurements and observations were made at both sites and special attention was paid to the performance of species during the harvest, transportation, and installation stages, as well as during recovery postinstallation. All species but false rock cress (Aubrieta cultorum) were found to be suitable for extensive green roof applications in northern climates, although there were variations of suitability among the species. Good, mediocre, and poor interactions formed between numerous species, displaying different levels of compatibility. Finally, all species were considered appropriate for a mat production system; species that failed to germinate, species planted postinstallation, the frequently displaced rolling hens and chicks (Jovibarba sobolifera), and false rock cress were exceptions. Overall, many species in this study displayed successful, well-rounded growth. Based on results, species and species combinations were recommended for extensive green roofs in northern climates.

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Hanging basket (HB) production alters the light environment in the lower canopy of ornamental greenhouses by intercepting and altering the spectral quality of incoming light. If shading is sufficiently high, the quality of the lower crops can be reduced. This work investigated changes in light quantity and quality at the lower crop level caused by HB production in Ontario, Canada. Light sampling occurred at three commercial greenhouse facilities throughout the Spring 2012 HB season. The greenhouses represented a range of HB densities (1.8, 2.4, and 3.0 baskets/m2) and different HB canopy architectures (one, two, and three tiers of HBs). Light samples were taken at three fixed locations within each greenhouse facility: outside, HB level, and lower crop level. Photosynthetically active radiation (PAR) was logged continuously at each location within each greenhouse environment. Spectral scans were made at each sampling location, within each greenhouse facility, at various times throughout the season to assess how HB production altered the red to far red ratio (R:FR) at lower crop level. As the season progressed, outdoor daily light integrals (DLIs) more than doubled from <20 to >40 mol·m−2·d−1. Light reduction caused by polyethylene films and structural components varied among locations, but remained steady throughout the season, averaging 48.3% for the three locations. As the HB crops matured, the rate of decrease in PAR at lower crop level varied according to facility and HB density with mean reductions of 42.5%, 32.6%, and 37.7% for the one-, two-, and three-tiered facilities, respectively. Mean lower crop level DLIs were all very similar, between 9.4 and 9.9 mol·m−2·d−1. Accordingly, there may be insufficient light below HB canopies to produce high-quality crops of many varieties of bedding plants that are commonly grown in Ontario. The one- and two-tiered systems reduced the R:FR at lower crop level by 14% and 10%, respectively, whereas the three-tiered system caused no reduction. More work is required to determine if the observed far red shift is sufficient to alter crop quality. These case studies provide a backdrop against which to help determine and interpret horticultural management strategies for a variety of greenhouse crops.

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The objective of this study was to determine the optimal controlled-release fertilizer (CRF) application rates or ranges for the production of five 2-gal nursery crops. Plants were evaluated following fertilization with 19N–2.6P–10.8K plus minors, 8–9 month CRF incorporated at 0.15, 0.45, 0.75, 1.05, 1.35, and 1.65 kg·m−3 nitrogen (N). The five crops tested were bigleaf hydrangea (Hydrangea macrophylla), ‘Green Velvet’ boxwood (Buxus ×), ‘Magic Carpet’ spirea (Spiraea japonica), ‘Palace Purple’ coral bells (Heuchera micrantha), and rose of sharon (Hibiscus syriacus). Most plant growth characteristics (i.e., growth index, plant height, leaf area, and shoot dry weight) were greater in high vs. low CRF treatments at the final harvest. Low CRF rates negatively impacted overall appearance and marketability. The species-specific CRF range recommendations were 1.05 to 1.35 kg·m−3 N for rose of sharon, 0.75 to 1.05 kg·m−3 N for ‘Magic Carpet’ spirea, and 0.75 to 1.35 kg·m−3 N for bigleaf hydrangea and ‘Green Velvet’ boxwood, whereas the recommended CRF rate for ‘Palace Purple’ coral bells was 0.75 kg·m−3 N. Overall, species-specific CRF application rates can be used to manage growth and quality of containerized nursery crops during production in a temperate climate.

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Commercially available Canadian retail potting mixes were evaluated for physical and chemical properties, as well as for plant performance of petunia (Petunia ×hybrida ‘Storm Pink’), tomato (Solanum lycopersicum ‘Better Bush’), and zonal geranium (Pelargonium ×hortorum ‘Savannah Red’) plants grown outdoors at the Vineland Research and Innovation Center in the Niagara Peninsula in Ontario, Canada. Chemical properties, but no physical properties, resulted in significant correlation with plant growth index, overall appearance, and yield (i.e., flower, fruit, or inflorescence number for petunia, tomato, and zonal geranium, respectively). The performance of all species was best when initial potting mix pH and electrical conductivity (EC) values were in the ranges of 5.20 to 6.17 and 2.76 to 4.33 mS·cm−1, respectively. The physical properties of the container capacity, total porosity, air space, and bulk density were acceptable for all plants in this study and ranged from 71% to 80%, 78% to 96%, 8% to 20%, and 0.08 to 0.22 g·cm−3, respectively. The minimum concentrations of the initial nitrate (NO3 ), ammonium (NH4 +), phosphorus (P), and potassium that were acceptable were 104.4, 61.3, 47.9, and 150.5 ppm for petunia and 96.8, 61.3, 51.7, and 143.3 ppm for tomato, respectively. The minimum concentration of NO3 that was acceptable was 66.1 ppm for zonal geranium. Overall appearance at 4, 8, and 10 weeks after transplanting was correlated with initial potting mix EC, NO3 , and calcium for all species, with pH, NH4 +, and P for petunia, with P for tomato at all time points, and with P for zonal geranium after 10 weeks. Although it is difficult to discern how each nutrient impacts plant performance, this study indicated that it is essential to have a balanced and adequate supply of nutrients in consumer potting mixes. The ability of a potting mix to maintain an appropriate pH for the duration of the growing season may prevent nutrient deficiency symptoms, especially for pH-sensitive species like petunia. This study is the first to provide a benchmark of currently available retail potting mixes for Canadian consumers.

Open Access

Hydrogen peroxide (H2O2) is an oxidizing agent used to disinfect recirculated irrigation water during the production of organic crops under controlled environmental systems (e.g., greenhouses). To characterize the phytotoxic effects and define a concentration threshold for H2O2, three microgreen species [arugula (Brassica eruca ssp. sativa), radish (Raphanus sativus), and sunflower (Helianthus annuus ‘Black Oil’)], and three lettuce (Lactuca sativa) cultivars, Othilie, Xandra, and Rouxai, were foliar sprayed once daily with water containing 0, 25, 50, 75, 100, 125, 150, or 200 mg·L−1 of H2O2 from seed to harvest under greenhouse conditions. Leaf damage was assessed at harvest using two distinct methods: 1) the percentage of damaged leaves per tray and 2) a damage index (DI). Applied H2O2 concentrations, starting from 25 mg·L−1, increased the percentage of damaged leaves in every species except ‘Black Oil’ sunflower, which remained unaffected by any applied concentration. Symptoms of leaf damage manifested in similar patterns on the surface of microgreen cotyledons and lettuce leaves, while mean DI values and extent of damage were unique to each crop. Fresh weight, dry weight, and leaf area of all crops were not significantly affected by daily H2O2 spray. Identifying how foliar H2O2 damage manifests throughout the crop, as well at individual cotyledon or leaf surfaces, is necessary to establish an upper concentration threshold for H2O2 use. On the basis of the aforementioned metrics, maximum recommended concentrations were 150 mg·L−1 (radish), 100 mg·L−1 (arugula) for microgreens and 125 mg·L−1 (‘Othilie’), 75 mg·L−1 (‘Rouxai’), and 125 mg·L−1 (‘Xandra’) lettuce.

Open Access

One principle for reducing undesirable stem extension in greenhouse production is to counteract the decrease in red-to-far red ratio that occurs naturally during twilight periods. This study evaluated three lighting treatments on the morphology of easter lily (Lilium longiflorum): 1) a 1-hour end-of-day treatment providing 20 μmol·m−2·s−1 of monochromatic red light (EOD R), 2) blackout curtains closed 45 to 75 minutes before sunset and kept closed until 0 to 60 minutes after sunrise (BO), and 3) a control with natural twilight (CTRL). Plants under the BO treatment were 11% shorter than CTRL, while plants exposed to EOD R did not differ in height compared with BO or CTRL. There were no treatment effects on any other measured parameters, including aspects of flowering.

Open Access