Pansy is one of the most popular annual bedding plants in the U.S. due to its frost tolerance and ability to provide color in winter in warm climates or late fall and early spring in colder climates. Pansy plants are often grown under black shade net ranging from 50% to 80% shading. The use of plant growth regulators (PGRs) in pansy production is also common to reduce stretching under the lower light levels.
The objective of recent studies by Bruce Dunn is a Professor of Horticulture & Landscape Architecture at Oklahoma State University, was to evaluate the effects of different colors of shade nets on controlling growth and flowering of pansy. In Experiment 1, ‘Clear Yellow’, ‘Buttered Popcorn’, and ‘Deep Orange’ pansy plugs were placed under 30% blue or black shade net or, as a control group, where grown with no shade net. In Experiment 2, the same three cultivars of pansy were grown under 50% black, red, pearl, or aluminized shade net.
Shade nets reduce air and canopy temperatures by physically blocking solar radiation including photosynthetic active radiation (PAR) around the crops and thus lowering thermal energy exchange. Shade nets can be used outside over the top of greenhouses to reduce whole-house radiation load, as well as inside greenhouses to create targeted shade leading to a suitable environment for crop growth in hot and sunny regions.
Colored nets are designed to manipulate plant development and growth physiology by affecting light quality via light spectrum modification upon filtering through the net. Colored shade nets have been reported to have the ability to modify ultraviolet light, visible light, or red-to-far red (R:FR) light ratios based on the colors of the netting and that light fraction hitting the colored threads becomes spectrally modified and scattered, while the light passing through the holes of the net remains unmodified in spectrum.
The studies showed that blue and pearl shade nets both led to a decrease in plant height, but blue shade nets also reduced plant survival and flowering. Pearl shade net showed the most overall potential for an alternative to chemical height control in pansy. Greater altered light spectral quality with greater amounts of blue light likely reduced plant growth. Pearl shade net had greater light intensity than red, aluminized, and black that could have resulted in reduced plant stretching. Light quality and quantity are known to affect plant growth. In both experiments, black shade net resulted in cooler temperatures, but aluminized was not different from black at 50%, making them better for cooler season crops.
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Future research will evaluate different cultivars of pansy, shade net percentages, and direct comparisons of pearl shade net with chemical plant growth regulators as a potential sustainable alternative.
Find the complete study information on the American Society for Horticultural Science’s HortTechnology website here.