Solarizing Your Garden to Rid it of Pests
Rather than relying on pesticides, fungicides and the like garden-upsetting chemicals to rid your plants of their pest woes, use the simple, free power of the sun to sanitize your soil. Simple plastic tarps can be used to raise the temperature of infected soil to mold, fungus, mildew, nematode, larva, and insect-killing levels, much as boiling water can sanitize medical instruments. A thin, clear plastic tarp is all that is needed, placed over the cleared, leveled patch of garden soil and anchored down with rocks or buried at its edges. You should water the affected area before laying the tarp down, and then eliminate air pockets as much as possible between the soil and the plastic sheet. Tomato plants can tolerate solarizing even while they are growing, but most plants will not enjoy the experience, so you might want to solarize your garden in shifts while other sections are producing your flowers, vegetables, and herbs.
Ideally, the soil should reach 130 F over a couple of weeks. A thermometer can verify the temperature elevation you're getting at different depths. You will also be better off using a thinner plastic sheet, and starting at the beginning of your summer, although this combination may mean that your plastic sheet is largely decomposed by the end of the 4-6 weeks.
Just remember, solarizing will kill more or less everything in the treated soil. Earthworms and the like may have migrated downwards to safety, but in order to kick start your garden's rebirth, using earthworm inhabited compost to repopulate the treated soil is an excellent first step - so long as you know that the compost isn't infected with the same pestilent agent you were trying to eradicate. On the other hand, don't turn the soil over, as this might bring up untreated soil from deeper down.
10/27/2009: Earth Clinic Planet writes: "Instead of using solarizing as an alternative to pesticides, some gardeners (particularly in cooler climates) use the solarizing technique to jump-start or extend their growing seasons. A number of plants, and in particular your popular tomatoes, peppers, and squash, require a soil temperature of 70F before they will grow happily and well. Many of us know just how late in the spring those sorts of welcome temperatures can arrive. Solarizing helps to warm the soil for planting a bit ahead of schedule.
About four weeks ahead of your intended planting date, clear the area of weeds and roots, turning the soil over just a bit in the process. Water dry soil, then place your clear plastic tarp down over the area to be solarized, sealing the edges with soil to keep colder air out. When you are ready to plant, you can remove the plastic sheet or simply cut holes in the plastic and insert your seedlings."
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10/24/2009: Earth Clinic Planet writes: "If you would like to use solarizing as a method to get rid of weeds, use a black plastic tarp or even one sheet of a black plastic garbage bag. The plastic will heat the soil to weed-defying levels, and the lack of light will seal the deal. Many folks use this tactic against poison ivy, although you should be careful about the oils left over on the plastic sheet after the treatment is completed. While we don't love plastic, this method is far superior to herbicide treatments."
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