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Managing light to enhance greenhouse growth
Since plant growth is influenced by the quality and quantity of light, Clemson scientists are studying ways to manage the light in greenhouses.

One study is investigating the use of retractable shade curtains to develop recommended management strategies. Curtains have been installed at the S.C. Botanical Garden greenhouses, along with gas exchange chambers to measure the effects of shading on photosynthesis and plant growth. Data has been collected and is now being analyzed for 12 different species grown under four different light levels. Another phase of this study will examine the effects of fluctuating shade versus constant shade on plant growth and development.

Another study measured the effects of hanging baskets on light transmitted to the greenhouse bench. This study showed that light transmission was reduced twice as much by closer spacing of the baskets (12” versus 24”) and by using green instead of white baskets. In addition, containers with plants reduced light three times more than empty containers; however, the red to far-red ratio was not affected by the presence of plants in the containers. 

These findings have been shared with commercial growers at conferences in Canada and the United States. The next phase of this study will be conducted at commercial greenhouses to validate the findings. In addition, contour maps showing the monthly solar radiation across the U.S. have been developed.
(For more information, contact Jim Faust jfaust@clemson.edu, Clemson Horticulture Department.)

In another study, scientists are studying plants' response to various greenhouse films that filter out specific wavelengths from the sunlight. This is part of the wide-ranging Clemson Photomorphogenesis Research that began in 1986. In early research, filtering out far-red light from the greenhouse by liquid CuSO₄ filters was shown to be effective in reducing stem elongation of plants. 

This  reduced the need for chemical growth retardants to control plant height. In the late 1990s, Clemson researchers established a collaboration with Mitsui Chemicals in Japan to develop and test photoselective greenhouse plastic films and facilitate commercial applications of this technology.

In the latest research, experimental far-red light absorbing photoselective greenhouse films have been shown to be effective in reducing stem elongation in a wide range of plants. Greenhouse covers with UV blocking ability have been shown to reduce disease occurrence and insect populations on greenhouse crops. Heat and UV light blocking films are currently available on the commercial market.  

If plant growth regulation, insect/disease control, and greenhouse heat reduction can be achieved from greenhouse films, this will be a tremendous advantage for greenhouse growers. With such films, the nursery and greenhouse industry could reduce costs for growth regulating and disease/pest control chemicals, reduce health risks to their workers and consumers, and reduce potential environmental pollution.
(For more information, contact Nihal Rajapakse nrjpks@clemson.edu, Clemson Horticulture Department.)

Technical articles:  
Growth regulating photoselective greenhouse covers
(pdf 325 KB)

Role of gibberellins in Chrysanthemum growth under far-red light deficient greenhouse environments
(pdf 325 KB)