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Using Cover Crops to Improve Soil


Green manuring, also known as cover cropping, is the practice of growing a crop and then tilling it under to enrich the soil. Although the two terms are often used interchangeably, green manuring is primarily done to add organic matter to the soil while cover cropping often is also used to prevent erosion. The crop that is turned under adds organic matter and nutrients to the soil. Cover cropping also greatly improves the structure of the soil and its tilth. Soils with loose, granular crumb structure are said to have good tilth, making them easily dug and tilled.

Properties with new construction are among the most likely prospects for cover cropping. Usually, the soil has been stripped away leaving a mixture of rubble and clay, not a likely soil for garden or lawn. If you take the time--a year or even two--to plant and till in a series of cover crops, the result will be a far more hospitable soil for sodding or sowing lawn grasses or installing trees, shrubs and gardens.

You can plant grasses or legumes as cover crops. Grasses are better at adding organic matter and stimulating soil life while legumes add more nitrogen when plowed under. If you plant a legume, you should first spread a commercially available inoculant on the soil or treat the seed with it before you plant. Make sure that you get the right kind of inoculant for the seed you are planting. Your seed supplier can help you with this.

Grasses, field rye, winter oats and wheat are good winter crops for green manuring. Sow them in late summer to early fall, then plow them the following spring. Spring cover crops include fast-growing garden peas, sweet clover and grasses. Sow them in very early spring, then turn them under before planting summer flowers and vegetables. Summer cover crops that will thrive in hot weather include buckwheat, millet, Sudan grass and sunflowers.

Mow the dense foliage of cover crops before plowing them under--this will break the foliage into smaller pieces and thus hasten decomposition. Plan to mow and plow under the cover crops well before they are mature, while the stems are still soft and easily cut. You can have two, three or even more cover crops in a single year with some careful planning. In the long run, green manuring or cover crops are a less expensive and more successful way to improve your soil than most alternative methods.

Use winter cover crops on annual and vegetable beds to replenish the soil and prevent erosion. Annual rye and ryegrass, two commonly used cover crops, should be planted by mid-September, then tilled into the soil in the spring. This practice adds organic matter, benefits the soil, and is a good way to keep gardens productive and vigorous.

Missouri Botanical Garden, 2001-2011