Soil Solarization to Manage Weeds and Diseases
Soil solarization is a technique we often read about to control severe weed and soil-borne
disease problems. The procedure is to cover problem soil with clear plastic and trap the
sun's heat to raise temperatures high enough to kill weed seeds and plant disease
This technique can be used somewhat effectively only in the hottest parts of our
northern states. It is also important to realize that an area that is receiving this treatment
will be out of production for nearly the entire growing season, and that weed seeds that
are buried deeper than 2, perhaps 3 inches in the soil will not be affected by the
procedure. Even so, for sites that are otherwise unusable, solarization can be an option
If you have found that weed or plant disease problems rendered your plot unusable and
would like to try solarization, till under existing weeds to prevent seed production and
make preparations to solarize in spring. It is suggested you try the method only if you live
in one of the warmest parts of the state. Cover the site with a weed- and disease-free
mulch until next spring.
To solarize soil, all you need is a roll of clear polyethylene plastic. The best types come
in 10-foot wide rolls and contain ultraviolet inhibitors. 2 to 4 mil thickness is most
durable. The longer the plastic stays in place, the better. For maximum effectiveness,
cover your soil for 14 weeks between June and September.
The first step is to till the soil well, then rake it free of large clods, weeds and plant
material. Be absolutely sure that the site is level, well-tilled, and smooth, providing
maximum contact between the soil surface and the plastic.
The second step is to use a sprinkler or drip-line irrigation lines to saturate the soil to a
depth of 3 feet or more. This can take hours, but it is essential for successful solarization.
Next, dig a 6-8 inch trench around the plot, then wet the soil again. To lay the plastic,
place one edge in a trench, then cover it tightly with soil. Stretch the plastic tautly over
the site, then bury the remaining edges. Leave the plastic in place all summer, making
sure the wind does not blow or lift the plastic, allowing heat and moisture to escape. In
late summer or early fall, remove the plastic. Do not cultivate the soil because that will
bring viable weed seed back into the upper 2-3 inches of soil. Cover the site with a weed
and disease free mulch, then plant the following spring. Remember, this method is most
effective in warmer regions of the country.
Controlling Pests and Diseases; Rodale's Successful Organic Gardening. 1994. Rodale
Press, Emmaus, Pennsylvania 18098. 160 pp.
Flint, M.L. 1990. Pests of the Garden and Small Farm. University of California.
Oakland, CA 94608-1239. Pub. #3332. 276 pp.
The IPM Practitioner. Bio-Integral Resource Center. Berkeley, CA 94707.
Written by Sherry Lajeunesse, Extension Urban Pest Management Specialist. Sept., 1997
Categories: Weed, Disease