Efficient use of space is critical to the success of commercial greenhouses. Many growers produce hanging basket crops in addition to the crops grown on the bench or floor. In 2012, the wholesale value of flowering hanging baskets in the United States was $211 million, while foliage hanging baskets were valued at $78 million (U.S. Department of Agriculture, 2013). The most popular species grown in hanging baskets were geranium (Pelargonium ×hortorum), impatiens (Impatiens wallerana), new guinea impatiens (Impatiens hawkeri), petunia (Petunia ×hybrida), poinsettia (Euphorbia pulcherrima), and begonia (Begonia ×semperflorens-cultorum).
Concerns exist about the effect of overhead baskets on the light environment delivered to crops grown on benches or floors below hanging baskets; however, quantified data are limited to a recent survey (Llewellyn et al., 2013). The percentage of light reflected or intercepted by the greenhouse glazing and infrastructure alone can range from 30% to 60% even without hanging baskets (Critten, 1986, 1989, 1993). Hanging baskets potentially impact both the light quantity and spectral light quality delivered to the underlying bench crop as leaves differentially absorb, transmit, or reflect photons (Deregibus, 1985; Holmes and Smith, 1977). PPF interception by hanging baskets will therefore reduce the daily light integral (DLI), delivered to the crop underneath. DLI has a great impact on plant quality because lateral branching and flower number for many species have been found to increase as the DLI increases (Chong et al., 2014; Faust et al., 2005; Holcombe et al., 2001). The presence of hanging baskets can also potentially affect the light quality delivered to the underlying crop by preferentially absorbing R (600–700 nm) compared with FR (700–800 nm). Red inhibits stem elongation, reduces internode length, and promotes lateral branching (Holmes and Smith, 1977), while FR promotes stem elongation, increases internode length, and reduces lateral branching (Runkle and Heins, 2001; Smith, 1982). Hypothetically, plants grown in hanging baskets will reduce the DLI and the R:FR environment for the crop underneath, thus increasing stem elongation and decreasing crop quality (Pasian, 1994).
A greater understanding of how hanging baskets affect the greenhouse light environment will allow for the optimization of crop production; i.e., maximizing hanging basket production while minimizing the reduction in bench or floor crop quality. Therefore, our objective was to quantify the effect of hanging baskets on the PPF and R:FR transmitted to the greenhouse floor, specifically examining the effects of hanging basket density, the presence of plants in the hanging baskets, and the container color.
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