A: Cover crops are grown to protect the soil from erosion and to be cut back and tilled into the soil in spring to increase its organic matter and nutrient content. They also help stimulate soil microbial activity, shade out germinating weed seeds and help loosen compacted soil as their roots grow.

Winter rye is the most commonly grown winter cover crop in our area because it is cold-tolerant and can be sown as late as mid-October, which gives gardeners time to harvest annual vegetables and remove spent annual flowers prior to planting. It is a winter annual grass that will continue to grow until temperatures drop to about 40 degrees and resume growth when temperatures warm in spring. Winter rye germinates quickly and tolerates wet or dry conditions, low fertility and acid soils.

It produces a substance that inhibits the growth of many weeds and other plants, so it is important to mow it down and till it in about four weeks prior to planting vegetables or flowers in the spring. All raw organic matter can tie up available soil nitrogen as it decomposes and cause a temporary nitrogen deficiency in crops, so working it into the soil early enough avoids that problem as well.

Winter rye produces a dense root system and lush foliage, so it can be difficult to till under. It helps to mow it short first. It may be easier to compost the clippings for later application to garden beds and till in the crowns and roots alone.

Certain legumes are often used as cover crops but really provide the most benefit if you plant them in spring and allow them to grow all summer, which can take too much valuable space in a home garden. Legumes are plants that have the unique ability to fix nitrogen from the air in association with soil bacteria, and they return that nitrogen when they are cut back and tilled into the soil. They also have extensive root systems and are a good choice to break up hard, compacted clay soils.

Their best use in home gardens may be to start new beds in places where the soil is less than ideal. Strip off the sod, plant a cover crop of legumes and allow them to grow for a season before working them into the soil. Plant the desired crops the following year. Legumes used for cover crops include clovers, hairy vetch and alfalfa. Be sure to cut them back before they go to seed, or they can make a nuisance of themselves.

To plant a winter rye cover crop, remove spent annual vegetables and flowers from the garden. Till up the soil to prepare a good seedbed, then broadcast the seed at 2 to 2 1/2 pounds per thousand square feet. Rake it in lightly and water to start the germination process.