On Gardening/Cover Crops Can Benefit The Garden

9-24-97
University Park, Pa. -- Cover crop use reduces soil erosion while maintaining and building nutrient supplies for your garden over the winter. Cover crops are often called "green manure" crops because they are grown for the purpose of being plowed or turned under before they mature. Such crops improve the physical condition of the soil by increasing its organic content which improves both structure and porosity to equal better drainage.

Winter cover crops can be planted from September 1 through mid-October. Where you still have fall garden crops growing, simply sow cover crop seeds between rows a month or less before you expect final harvest. This way the cover crop gets a good start but will not interfere with your vegetable plant growth.

Prepare the soil for the cover crop seed by tilling under plant waste from the summer. If the garden site is not too fertile, apply several pounds of a complete fertilizer such as 10-10-10 per each 100 square feet of area sown to the cover crop. Little will be gained from growing a cover crop on land too poor to support good plant growth. Broadcast the seed, preferably before a rain, and rake it evenly into the soil.

Spring planting may be delayed somewhat by the practice of cover cropping, since time must be allowed next spring for the green manure crop to break down after it is incorporated into the garden. If you have crops that need to be planted very early, you may prefer to cover a section of the garden with a mulch to protect the soil over winter.

The most valuable cover crops, from the standpoint of increasing the fertility of the soil, are the legumes. Hairy vetch is a winter annual and valuable as a soil builder. Inoculated seed is best sown in early September at a rate of about one quart of seed per 1000 square feet of area. Best growth is obtained in a well-drained soil with a pH of 6.5. This cover crop should be turned under about the middle of May when the top and roots contain between 3 and 4 percent nitrogen.

Rye is considered to be the most valuable of all nonlegume cover crops. Although it does not contribute nitrogen to the soil, it adds a considerable amount of organic matter. Sow in early September at a rate of about three quarters of a quart of seed per each 1000 square feet of area. Rye succeeds quite well on a soil with average fertility and is indifferent to soil pH, doing very well on acidic soil.

Rye should be plowed or turned under in the spring when it is about 10 inches tall. At this time the plant contains a greater percentage of nitrogen than at any stage of development. If the top growth is not incorporated, it can be harvested and used as a mulch during the season. The roots and stubble will enhance soil organic matter.

Next spring you might want to consider the sowing of other legume cover crops such as soybeans, alfalfa, clovers or the vetches. Most of these do better as a spring crop that is sown quite early. These legume crops will also have to be incorporated before they mature and the stems become too woody. These plants should not be allowed to set seed in the garden, because they could become a weed in the future.

It is also important to remember that crops planted immediately after the incorporation of a cover crop (especially nonleguminous crop) will do better if a fairly liberal application of complete fertilizer is made at the time the cover crop is turned under. The added fertilizer provides nitrogen that aids the soil bacteria and fungi as they decompose the added organic matter.

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**Dr. Robert Nuss is a horticulturist at Penn State. He coordinates all extension horticulture programs. He has bachelor's, master's, and doctoral degrees in ornamental horticulture and has been on the Penn State faculty since 1966.