Building Fertile Soil

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"The best mulch will be had," Weil says, "if the cover crop is allowed to grow until it 'heads out' or flowers, and if high-residue cover-crop species (such as rye) are included in the mix." However, if the cover crop residue is too thin to completely cover the soil, Weil recommends spreading a couple of inches of mulch to cover the soil well. To set out transplants, he simply makes a hole in the mulch and digs out enough soil to accommodate the root ball. The soil is replaced, and mulch is pushed around the transplant. Seeds can be planted by making a narrow part in the mulch with a rake, then drawing a small furrow with a pointed stick in which to sow the seeds. If the soil is too firm, Weil pulls an old meat hook or curved crowbar through it like a single tine on a harrow; the zone of disturbed soil need be only a couple of inches wide.

Once a permanent bed is established, feed the soil food web regularly. Elaine Ingham, president of Soil Foodweb Inc., a firm that specializes in growing plants without pesticides and inorganic fertilizer, says the best way to manage a healthy microbial ecosystem in a home garden is to routinely apply organic material such as compost.

Ingham suggests gauging the amount needed by what has disappeared from the soil during the previous season. Generally, adding one-half inch to 1 inch of compost every spring will be plenty. In hot climates, where decomposition is rapid, or in regions with heavy rainfall or sandy soil, make at least two 1-inch applications, one in early spring and the second in late summer or early fall.

MULCH IS A MUST

Beyond the obvious benefits of suppressing weeds and preventing soil crusting, mulch helps maintain the soil food web. Mulch dramatically increases the amount of rainwater that enters the soil and decreases the amount of water that runs off the surface. Runoff takes soil with it, damaging the food web. Even modest mulch or cover crop coverage (10 percent to 30 percent), Weil says, substantially improves rainfall saturation and erosion control. (In some areas, mulch may keep the soil too wet or cool, in which case you can rake some of it back to allow the soil to warm up and dry out.)

Organic mulch also feeds soil microbes. Earthworms move organic matter from the surface down to root zones where it can be used by bacteria. Many diseases are prevented or slowed by beneficial fungi living in mulch. A North Carolina State University study showed that only 3 percent of tomatoes mulched with composted cotton gin trash became infected with Southern blight, a fungal disease, compared to 66 percent of unmulched control plants. The composted mulch was an ideal breeding ground for beneficial fungi (Trichoderma), which killed or prevented the blight. Numerous disease-causing bacteria and fungi are found in the soil, but a healthy, diverse soil food web, nourished by mulch, allows beneficial microbes to naturally control or eliminate those that cause problems.

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