Extension Service Garden Hints

What is soil solarization?

CORVALLIS - Over the past few years, agricultural scientists at Oregon State University and the U.S. Department of Agriculture (USDA) in Corvallis have been experimenting with a simple, non-chemical means of combating plant diseases and weeds called "soil solarization."

Researchers are finding that soil solarization reduces populations of soil pathogens such as Verticillium wilt, crown gall, root-lesion nematode and Phytophora root rots to a depth of almost a foot under the soil surface, explained Jack Pinkerton, plant pathologist with the USDA in Corvallis. They also are seeing that solarization decreases weeds and other pests, some species more than others.

Soil solarization is a fancy term for the simple process of putting transparent plastic sheeting over tilled soil during the warmest and sunniest two months of the year. Soil solarization is easy to do in your home garden.

The plastic traps the heat of the sun. Under plastic sheeting, the top few inches of soil can be as much as 20 degrees warmer than uncovered soil. In this extra-warm environment, disease-causing organisms tend to flounder while more heat tolerant "beneficial" microbe species increase in numbers. Also, the heat eliminates some kinds of pests, weed seeds and seedlings.

Scientists term this change in the soil microbial community after solarization as a "microbial shift," said Pinkerton, also a courtesy faculty in OSU's Department of Botany and Plant Pathology.

Microbe-caused changes may also make more nutrients available to plants in solarized soil. Agricultural scientists all over the world are testing solarization and are finding that this simple technique may be a more environmentally friendly alternative to soil fumigants or other fungicides in some cases.

By: Carol Savonen
Source: Jack Pinkerton

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