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Revitalizing your garden soil can be as simple as planting the right cover crops.
One of the best things gardeners can do for their soil is add organic matter. Compost, manure and rotted leaves are all great soil amendments —but have you considered growing organic matter in place? This ancient technique of improving soil is called cover cropping.
Growing cover crops, sometimes called green manures, is fairly simple. Plant a crop you do not intend to harvest, and when it reaches a certain level of maturity, mow it down and till it into the soil. The crop decomposes in the soil, feeding soil microbes, improving soil structure and releasing nutrients that future garden plants can use.
Cover crops also prevent soil erosion, suppress weeds, reduce pest and disease problems, and capture and recycle nutrients left over from previous crops.
Typically, cover crops are combination plantings of grains and legumes (bean relatives). The grain provides bulk roughage, sometimes referred to as biomass, while the legume captures nitrogen from the air and “fixes” it into the soil, making it available for later plantings. Cover crops are annual plants, living for only one season, and are broken out into summer and winter crops. Seeds for these crops are usually available at your local feed-and-seed store but can also be purchased online.
Obviously this technique is best suited to vegetable gardens, where crops are changed out each season, but it can be used to build soil for flower and perennial beds. Crop rotation is an important component of managing plant diseases in a vegetable garden. I use cover crops as a part of my overall rotation plan. To manage crop rotation, group your vegetables into related families. Tomatoes, peppers, eggplant and Irish potatoes, for example, are all members of the nightshade family and share similar pests and diseases. To minimize these problems, family members should not be planted in a particular spot in the garden more than once every three years. Cover cropping provides a season or even a whole year of non-production while improving the soil.
Here’s how I do it. In the spring, I plant all my nightshade crops together. Once they finish producing, I pull them out and prepare the soil for a winter cover crop. My go-to for this season is a mix of oats and crimson clover, broadcast over the rows in September. They slow their growth in winter and start producing flower buds in early spring; this is the time to mow them down and till them into the soil. Plants have the highest amount of nutrients just before they flower, so tilling them in at this time provides the greatest soil benefit. Plow your cover crop under at least a month before your desired planting date so it will decompose before planting.
I like to follow a winter cover crop with a summer cover. This gives a full year for diseases to dissipate and soil to rebuild. My preferred summer cover crop is a mixture of buckwheat and cowpeas; in a typical summer, this combo can be planted and plowed under twice. In subsequent seasons, I rotate through other non-nightshade vegetable families, so I’m not replanting tomato relatives in that area until the three-year rotation is complete.
Even in my small vegetable garden, this strategy keeps my soil and plants healthy and productive.
S. Cory Tanner is an area horticulture agent and Master Gardener coordinator for Clemson Extension based in Greenville County. Contact him at shannt@clemson.edu.