Cover crops conserve nutrients, support a high biological activity and produce a superior soil structure. When you plow them into the soil, they're sometimes called "green manures."
Green manures offer succulent growth which decomposes easily in the soil, releasing nutrients. While they're smothering weeds, they keep nutrients from leaching, too, and protect the soil over the winter.
Cover Crops Improve Soil
Cover crops are any plant you sow into the garden that improves the soil. The actual benefits depend on the plant type and how much you grow.
Annual cover crops are usually grown as green manures. That is, they are turned into the soil while still green, normally just before they flower. Their greatest value is usually in the top growth. But the roots are often beneficial, too.
Varieties of green manures are chosen for their fast, vigorous growth and high production of green, succulent top growth.
The green matter decomposes quickly in the soil. When it does, the result is a flush of biological activity and a quick release of nutrients, some of which the roots may have accumulated from the subsoil. The succulent residues replace some of the humus, building a dynamic soil system.
The downside of growing a green manure is that it requires the land be left idle for a time. That's unpopular with many gardeners.
However, crops other than legumes may be grown as "smother crops" to control weeds. Commonly used as a winter cover and catch crop, they protect the soil from erosion and conserve nutrients otherwise lost.
Good Cover Choices
Traditional choices for green manures are buckwheat, small grains such as rye and oats and annual grasses such as rye grass and wheat.
Other crops are possible, however. Rapeseed, for instance, makes a good green manure. But don't follow it with another planting of the cabbage family.
Sometimes legumes are grown. Austrian winter peas are commonly planted in the fall for overwinter growth where winter temperatures aren't severe.
The green manure sod not only feeds soil organisms but protects the soil from direct sun and rain.
Over the years, the combination of the high biological activity and the extensive root system of grass leads to a superior soil structure and a slow, but steady, increase in soil humus.
When a green manure sod is plowed under, a rapid breakdown occurs with a sudden release of nutrients stored over a long time. That's why a cultivated crop following a green manure sod is usually very successful.
To learn more about green manures and other cover crops, contact the local county Extension Service office.
