Teague: How to solarize your garden plot

FresnoAugust 16, 2013 

Were your tomato plants puny and unproductive this summer? When you pulled them out, were the roots small, brown and knobby? These can be symptoms of a nematode infestation. Nematodes are microscopic worms that live in the soil and invade the root systems of susceptible plants, interfering with the plant's ability to draw up nutrients and water.

Did the edges of the leaves on your bean plants shrivel up and did the plants look as though they were drought-stricken even though you gave them plenty of water? If so, your beans may have been affected by verticillium wilt, a soil-born fungus that impedes plants from drawing up water.

Nematodes and verticillium wilt are two of the many destructive soil-born pests and pathogens that can be controlled with soil solarization. Soil solarization uses the sun's hot rays to heat the soil to temperatures high enough to kill or reduce populations of harmful fungus, bacteria, weed seeds, Bermuda grass rhizomes, and pest insects and their eggs. Soil solarization is cheap, easy, effective and fast in our climate. Within four weeks (from May through September), soil temperatures in the top six inches of soil will reach 140 degrees, hot enough to kill most disease pathogens and soil-dwelling pests that live in that top layer of soil. Temperatures in the next layer, from 6 to 12 inches deep, will be hot enough to kill a good percentage of pathogens and pests. Nematodes are mobile and some will escape into cooler, deeper layers during solarization and eventually move back to surface layers. Control for nematodes by solarization is not complete.

Soil solarization takes just four steps.

1. Clear the area to be solarized of all plants, weeds, surface rocks and debris.

2. Level and smooth the soil.

3. Irrigate the soil thoroughly; wet soil conducts heat better than dry soil.

4. Cover the area with a 1 to 4 mil thick layer of clear plastic and seal the edges of the plastic completely with soil.

After four weeks, remove the plastic. Replanting can begin immediately. You might think that all micro-organisms would be killed off by solarization, but one of the many benefits of solarization is a surprising increase in the numbers of beneficial fungi after the process is complete. Amendments really aren't necessary after solarization. Earthworms also move away from the hot soil and their populations will increase as they move back into healthy, solarized soil.


Elinor Teague is a Fresno County master gardener. Send her plant questions at etgrow@comcast.net or features@fresnobee.com ("plants" in the subject line).

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