Soil solarization: Solarization is a method of using the sun's heat to pasteurize the soil. Clear plastic is spread over the area to be treated during the hottest part of summer and left in place for 4 to 6 weeks. During this time, the soil temperature can reach 140°F near the surface and over 100°F 18 inches deep, which is hot enough to kill most insects, weed seeds, and disease organisms, including fusarium, verticillium, and rhizoctonia fungi. Nematodes are somewhat resistant, but some measure of control is achieved. Many beneficial microorganisms survive solarization or are able to recolonize rapidly after the soil cools. Exceptions are the nitrogen-fixing bacteria associated with pea and bean roots, which are completely killed. Use a pea or bean inoculant the first time you plant legumes after solarizing.

Follow these steps to solarize a garden plot:

1. Select the hottest time of year to solarize, usually June or July.

2. Cultivate the soil thoroughly and smooth the surface so the plastic cover will make uniform contact with the soil.

3. Water well. The moisture activates dormant organisms to make them more susceptible to the heat, and also helps conduct the heat deeper into the soil.

4. Spread clear polyethylene film over the area. Cover the edges and any seams with soil to prevent air from circulating under the plastic. One mil film is most effective at creating heat, but is fragile. If the area is windy or small animals are likely to run across the film, use up to 4 mil plastic.

5. Leave the plastic in place for 4 to 6 weeks. The longer time is more effective.

6. Remove the plastic after 6 weeks. If you leave it in place longer, it may become brittle from exposure to ultraviolet radiation and be difficult to remove. You can plant the next day.