Cover crops conserve nutrients, support high biological activity and produce superior soil structure. Plowed into the soil, it's 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 winter.
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. They are turned into to 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. If nematodes are a problem in the garden, you can reduce their numbers by planting a cover crop.
Varieties of green manures are chosen for their fast vigorous growth and high production of green, succulent 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 garden to be left idle, and that can be unpopular with many gardeners.
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 that would otherwise be lost.
Traditional choices for green manures are buckwheat, small grains such as rye and oats, and annual grasses such as ryegrass and wheat. Other crops are possible. Rapeseed, for instance, makes a good green manure. But don't follow it with another planting in the cabbage family.
Sometimes legumes are grown for a cover crop. Australian winter peas are a good choice to improve the soil.
The green manure sod also protects soil from direct sunlight 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 us usually very successful.
During this time of the year, white spot disease can be a problem on turnips, mustard and collards. It does not kill the plants, but it will cause spotting and necrotic areas on the leaves. The disease is favored by wet weather (which we certainly have not had), but overwatering can also cause the disease. Water your plants early in the morning when dew is already on them so the moisture will dry as the day progresses.
Excess nitrogen also favors infection, so avoid using too much. Mulches such as pine or wheat straw or bark are helpful in keeping the soil from splashing on the plants and will reduce infection. If only a few leaves have the infection, simply pick them off and destroy them. Available fungicides for control are any copper or sulfur based products.
Reach Sid Mullis, the director of the University of Georgia Extension Service office in Richmond County, at (706) 821-2349 or firstname.lastname@example.org.