Height Control of Greenhouse-grown Pansy Using Colored Shade Nets

Pansy (Viola ×wittrockiana) is a greenhouse crop commonly grown under black shade net; it often requires the use of chemical plant growth regulators to maintain a compact growth habit. Nonchemical efforts to alter plant morphology, such as height, would provide a more sustainable solution than chemical application. The objective of these studies was to evaluate the effects of different colors of shade nets on controlling growth and flowering of pansy. In Expt. 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 Expt. 2, the same three cultivars of pansy were grown under 50% black, red, pearl, or aluminized shade net. Data were collected on plant height, plant width, flower number, plant survival, soil plant analysis development chlorophyll meter (SPAD) readings, and light quality. In Expt. 1, the blue shade net reduced height to flower and height to leaves, but also decreased flower number and plant survival as compared with black shade net. All plants under no shade died. In Expt. 2, SPAD, an indicator of plant quality by estimating leaf greenness, was found to be lower under black shade net, whereas pearl shade net led to a decrease in plant height and no effect on the number of flowers. Light quality, including red-to-far-red ratio, varied among shade treatments, whereas light intensity was reduced under aluminized, black (50%), and red shade nets compared with other shade treatments. Blue and pearl shade nets both reduced plant height, but blue shade net also reduced plant survival and flowering.