Most Effective Ways to Utilize Sun’s Heat for Soil Preparation

In the article “Solarization Isn’t Something New Under Sun” by Kevin Connelly (Aug. 4, K7), which dealt with soil preparation using the sun’s heat trapped under plastic tarps to kill weed seeds and diseases, the following information on how to proceed was omitted:

The method is most effective where average high temperatures range above 90 degrees for six to eight weeks. West- and south-facing slopes respond better to solarization than cool north and east exposures.

Plan to spread the work over two days. For best results, the soil should be thoroughly cultivated, although this may not be practical on slopes. On more level ground, organic amendments, fertilizers or soil polymers can be dug or roto-tilled into the soil. Next level and rake the soil to remove stones, twigs and other litter that might tear the plastic tarp. Finally, irrigate the plot to wet it to the depth of one inch. This increases the soil’s capacity to hold heat.

The following morning lay the tarp while the air is still calm. Cover the plot with clear (not black) polyethylene sheeting. We found this in several widths in the paint department of a warehouse-style outlet.

At the Theodore Payne Foundation (which operates a native plant nursery where the procedure may be seen at 10459 Tuxford St., Sun Valley, (818) 768-8102) the sheeting used is 6 mils thick, sturdy enough to withstand some rough treatment up on the hill.