Magazine article Sunset

Using the Sun to Clean Up You Soil

Magazine article Sunset

Using the Sun to Clean Up You Soil

Article excerpt

Using the sun to clean up your soil

At the height of summer, when the sky isclear and the weather is warm, take advantage of the sun's energy to clean up your soil.

The process we describe here is called soilsolarization: you spread a thin sheet of clear plastic over cultivated soil to rid it of weeds and harmful organisms--without using chemicals. Trapping the radiant heat energy from the sum causes soil temperatures to rise to levels that are lethal to many bacteria, fungus, nematodes, and weed seeds. In hottest climates, benefits can last up to three years.

Extensive testing by researchers at theUniversity of California shows that solarization can control many soil organisms familiar to home gardeners--crown gall, fusarium wilt, verticillium wilt, and dozens of weeds. Nematodes are tougher to kill with this method, but control is usually enough to improve growth of shallow-rooted annuals and vegetables.

A few heat-resistant weeds--Bermudagrass and red clover, for example--are also tough to get rid of with this method. But the list of resistant pests is short compared to the many common organisms sensitive to the high temperatures, which can easily reach 140| two inches below the soil.

Researchers have also found that solarizationenhances activity of some beneficial organisms and increases available nutrients, resulting in improved plant growth.

Who can use solarization?

Soil solarization can work in almost anyclimate, since all it takes is four to eight weeks of clear skies during the hottest time of the year to accomplish the task. The warmer the climate and the longer you leave the plastic on, the deeper the effect. You'll also get better control of the harder-to-kill weeds like crab grass and nut sedge.

In coastal climates, this method isn't aseffective; fog, cloud cover, and wind interfere with heat transmission, and heat may not extend as deeply into the soil as in hotter climates.

If you attempt soil solarization when temperaturesare below 70|, increased weed growth often results. The method, however, does work to eliminate seeds if you cultivate the weeds before they go to seed.

Last year, we conducted our own test atSunset. During most of the test, temperatures ranged in the low to mid-70s, and mornings were often foggy.

In the solarized plot, we kept the plasticon the soil for eight weeks (if you're short of time and your climinate is warm--over 90|--you can remove plastic in as little as four weeks). …

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