Mulch? Tomatoes prefer red.

Mulch? Tomatoes prefer red

Gardeners are encouraged to mulch their plants to reduceweed growth and moisture loss in the surrounding soil. Some experts recommend mulching with whatever is least expensive in your area, such as wood chips, straw or shredded newspapers. Others recommend opaque plastic for its ability to collect and retain heat, often a benefit to tender seedlings set out in the cool spring. But gardeners may find it most profitable to focus on the color of their mulch, rather than what it's made from, according to scientists at Clemson (S.C.) University and the U.S. Department of Agriculture's Coastal Plains Soil and Water Conservation Research Center in Florence, S.C. Their preliminary work indicates that the color of the light a mulch reflects back onto a growing plant can significantly affect its growth.

Early work by USDA's Patrick G. Hunt and Michael J.Kasperbauer showed that by affecting phytochrome, a color-sensitive substance, even five minutes of colored light at the end of the day could alter the shape and size of a plant. For example, Hunt says such brief exposures to red light (600- to 700-nanometer wavelength) left soybeans, wheat and peas more spindly and smaller-rooted than plants exposed to farred light (700 to 770 nm) at day's end.

The next logical step was to see how the color of the soil--orthe mulch covering it--might affect seasonal growth. "To our surprise,' Hunt says, in experiments with tomatoes last year, "the red mulch gave us larger fruit and even increased the total number of fruit.' Relative to black mulch, it improved yields 20 percent. This year's surprise, he says, he how well white mulch appears to be improving bell pepper and potato production over yields in sandy (light-colored) soil and plots mulched with straw painted yellow, red or blue. It suggests, he says, that each plant may have its own preferred color.

Moreover, he adds, since the photochrome chemistry thesemulches appear to be affecting can be temperature sensitive, similar plants grown under different seasonal conditions-- hotter summers or longer days--may require some spectral fine-tuning to yield comparable results. Finally, he notes that his preliminary studies have focused only on changes in yields and morphological factors like stem length. Still to be studied is whether changes in reflected spectra will alter characteristics like taste, shelf life or susceptibility to blights.