To help commercial nurseries keep plants uniform in size, University of Florida researchers are testing colored plastic films that filter out growth-promoting light waves.
Sandy Wilson, an assistant professor of environmental horticulture with UF's Institute of Food and Agricultural Sciences, said the photo-selective plastic film in her current experiment filters out far-red light, which is responsible for stem elongation in plants.
“When grown in a greenhouse covered with photo-selective film, plants respond to subtle changes in the amount of far-red light they receive. The goal is to inhibit stem elongation without sacrificing plant quality.”
The horticulture industry prefers uniform plant size because it speeds plant establishment in the field and makes it easier to pack and ship mature plants. Traditionally, chemicals have been used to control plant height, but because of increasing environmental concerns, researchers are pushing the envelope to find other methods to control plant height.
Wilson has been testing the new film on sub-tropical annuals and perennials at UF's Indian River Research and Education Center in Fort Pierce, Fla., where she has obtained favorable results.
“Most plants grown under the far-red light absorbing film are about 25 percent shorter than plants grown under clear film, which is used as a control standard to compare effects of the colored film,” Wilson said. “The results are comparable to plants treated with chemical growth regulators.”
Nihal Rajapakse, a professor of horticulture with Clemson University and Wilson's colleague, was involved in the early stages of the colored film experiments. He said the idea for the green polyethylene film — which also comes in other dye colors to affect various plant characteristics — has roots in the early 1980s, when greenhouse panels filled with liquid dye were widely investigated for filtering out infrared radiation to control temperature.
Later, researchers used other liquid dyes that contained pigments to absorb far-red and other light wavelengths. The dye-infused panels were successful, so the next natural step was finding a less-expensive material that was easier to use.
In 1997, Clemson teamed up with Japan-based Mitsui Chemicals to develop the polyethylene films now being tested.
Mitsui, which manufacturers the polyethylene films, contracted with UF and several other institutions to test the green film in various regions of the United States. Ohio State University and Clemson are testing plants from their regions, and UF is testing southern plants.
“Because of Florida's warm climate, we can grow sub-tropical plants,” Wilson said. “This was a good trial because many of the species we worked with in Fort Pierce were traditionally ‘leggy’ meaning they grow fast and are extremely elongated. The good results with these plants bode well for other species.
Wilson said UF is also testing the polyethylene film to determine if it degrades faster in hot regions.
“One of the problems we have encountered has been a short film life,” Wilson said. “The dyes start to degrade after one year, so research is being conducted to increase the stability of the dyes.”
Wilson said the only other problems involve delayed flowering time for certain species.
“Because photo-selective film has different effects on certain species, growers may need to group plants accordingly in the greenhouse setting,” Wilson said.
In addition to ornamental plants, the colored films have been used on food plants such as bell peppers, tomatoes and watermelons.
“The potential applications are extensive and exciting,” Wilson said. “Once the kinks are worked out, plant growth regulation without chemicals will be the future of the industry.”