Got it covered?

04/09/2002
Got it covered?

If you don't use cover crops--aka green manures--in your garden, it's time to begin. A cover crop is simply a plant you sow, allow to grow for a while, and then turn under and allow to decompose--hence, "green manure." There is no more painless or effective way to enrich the soil while suppressing weeds than planting and then tilling in the appropriate cover crop.

French gardeners are firm believers in the power of cover crops. The lush patch of red clover above was photographed in the beautiful potager of St-Jean-de-Beauregard south of Paris. Even in public spaces such as Paris' Jardin des Bagatelles in the Bois de Boulogne, phacelia is regularly sown in the fall as a winter cover crop.

Cover crops can be planted throughout the year in Zones 7 and southward. In northern areas, they can be sown almost throughout the year--that is, from late winter or very early spring through mid to late fall. When you plant depends not only on your climate but on which cover crop plant you choose. Some are adapted to cool-season growth. Others are best spring planted, allowed to grow lushly for at least part of the summer, and then turned under before winter.

The hard part for the gardener is that--unless you're planting a winter cover crop--you're likely to feel as if you're "giving up" part of your garden space for the time the cover crop is in place plus a few weeks thereafter while it decomposes. But instead of thinking of cover cropping as a loss, consider it an investment. Even if you only rotate a tenth of your vegetable garden through cover cropping, from a soil-enrichment point of view, it's money in the bank. It also gives the cover-cropped patch time to cleanse itself of pathogens, pests, and weeds.

While all cover crops add priceless organic matter to the soil, they differ in their other specific benefits. Flowering crops, such as vetch, clover, phacelia, mustard, and alfalfa, provide forage for honey bees and attract other pollinators. Even more important, they attract beneficial insects (good bugs that kill bad bugs) to your garden.

Other covers fix atmospheric nitrogen, trapping it in plant-usable form in your soil. This is, quite simply put, free fertilizer. All the bean-family covers, such as clover, alfalfa, lupines, cowpeas, and vetch, do this. Deep-rooted cover crops such as blue lupine, clovers, alfalfa, rape, mustard, and vetch, act as biological plows, breaking up hardpan soils and simultaneously extracting subsoil nutrients and bringing them to the surface soil layer. Sweet clover, mustard, lupine, and buckwheat even extract phosphorus from the soil and make it available to succeeding plantings. This is especially valuable in clay soils where phosphorus is tightly bound to soil particles.

Finally, many covercrops have an allelopathic effect--that is, they secrete compounds into the surrounding soil that inhibit the germination of weeds. You can think of these covers (buckwheat, rye, sorghum, sudangrass) as natural, pre-emergent herbicides.

To sow a cover crop, simply broadcast the seed and rake it in. Take care to cover large-seeded crops more deeply. Allow to grow until at least 6 inches tall; then cut with a mower and till or spade it all under. Wait around three weeks or more before planting.

A few cover crops are perennial. These need to be used with caution by organic gardeners not willing to spray them with herbicide before tilling them. Live plant fragments are likely to regrow. If you really want to use a perennial cover crop organically, you do have the choice of smothering it with black plastic for a few weeks to kill it instead.

You needn't limit your use of cover crops to the vegetable garden. There's no better way to prepare a perennial bed or shrub border, or even a new lawn. If cover crops are so great, why don't more people use them? In my opinion, it's because cover crops require a bit of patience and tolerance for a delayed reward. In our speedy society, that's not always easy. But try it anyway. Slow down enough to allow cover crops to work their magic in your garden.

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Products of Interest:
'Jardinier' garden spade
Provenandccedil;al garden fork
'Paris' garden fork
Provençal garden and transplant spade