A cover crop is a fast maturing and growing crop that is grown to be tilled back into the ground without harvesting. Cover crops help to retain the soil, lessen erosion, and decrease the impact of precipitation on the garden by slowing the runoff of water. They also reduce mineral leaching and compaction, and suppress perennial and winter annual weed growth. The purpose is to add organic matter and nutrients to the soil.

You'd dedicate an area of your garden for cover cropping and plant seed (such as buckwheat) either in spring or summer for a summer cover crop or many gardeners plant a fall or winter cover crop in fall after their main crops are finished producing. These could be annual ryegrass or winter wheat for example. The key is to let them grow and before they flower and go to seed, till the crop in to add the organic matter.

Cover crops are used most often in vegetable gardens but are also appropriate for annual flower beds. They can even be used before planting a lawn or other landscaping to improve the entire area.

There are several different cover crops to choose from. They have many different advantages and disadvantages. Some of the most common are alfalfa, barley, buckwheat, crimson clover, oats, winter rye, hairy vetch, and winter wheat. 

* Alfalfa has long roots that can reach deep into the soil, bringing to the surface nutrients that would not otherwise be available to shallow-rooted vegetables. Because perennial alfalfa can grow some roots so monstrous that they become hard to manage, and even return to haunt the garden, the annual alfalfa `Nitro' is a better choice for home gardeners. It is much more docile, dying over the winter and leaving a mat of stems and foliage to be tilled in at your convenience in the spring. Alfalfa is also a magnificent bloomer -- a trait it shares with other legumes.

* Annual ryegrass is also used as a cover crop. It comes up within days of planting, tolerates alkaline soil, helps break up clay and is good at suppressing weeds. It can be planted any time. It has a vigorous root system that makes it hard to till under once it is established. It regrows readily after mowing. Annual ryegrass also can persist like a perennial, making it a potential weed when used as a winter cover crop. Some gardeners use annual ryegrass as a companion crop for crimson clover.

* Buckwheat is a good cover crop to use in late spring or early summer. It provides lots of green material to turn into the soil, is high in phosphorous and especially good for weed suppression. In my garden it kept bindweed from growing for an entire season. Buckwheat can be tilled into the soil as early as five to six weeks after planting.

* Crimson clover is also usually grown in the fall but can be grown as a summer annual. It has good cold tolerance, good nitrogen fixation capability, moderate drought tolerance and moderate to high shade tolerance. It is very quick to establish and will overwinter if it has not reached the bud/early bloom stage before the start of cold weather. The ideal time to turn it under is by early bloom before the flower color starts to fade. Mowing will also kill the crop, but this must be done no later than full bloom to prevent reseeding.

* Spring barley is an early cover crop that is similar to oats in growth characteristics. It is also susceptible to disease and occasional winterkill. Barley produces a large amount of leaves, but most of its growth comes late in the spring. Winter barley is also available, but is only slightly more winter hardy than spring barley.

* Subterranean clover is moderately tolerant of acid soils, has low shade tolerance and reseeds well. It is a low-growing, dense legume which produces seed below the soil surface. Because of its reseeding ability, it has been used as a living mulch. In New Jersey, subterranean clover seed matures and the plant dies back in mid-June. The succeeding crop is established by early September.

*Winter rye planted in the fall will germinate quickly and grow until the ground freezes, then provide erosion control through the winter. Winter rye should be sown in the fall and turned under in the spring. In mid March, till the winter rye under and let it die. If you wait until April or May to turn winter rye under, it will have grown so much you'll have to chop it down first. The stalks should be saved and can be used as an organic mulch later in the season. 

* Winter wheat is most suitable for mid to late season plantings. Plantings before late September are susceptible to disease and premature death. Winter wheat covers the ground quickly in the fall, but does not grow as vigorously as rye does in the early spring, making it a good choice for late planted gardens. Wheat is more leafy than rye, so it may decompose faster when it is turned into the soil.

Whatever plant you choose as a cover crop be careful not to let it go to seed before cutting or tilling it. The whole idea of a cover crop is to reduce the weeds in your beds, not to add more seeds. And while alfalfa and other perennials are often praised as cover crops, it takes considerably more work to till their larger root systems and mix them into the soil.

Buy seed of cover crops at your garden center or feed store. If specific seeding information isn’t available for each variety, use about 1 to 1½ cups of seed per 100 square feet. Spread it by hand, rake it into the soil and water regularly until it comes up. After the plants have grown at least 3 or 4 inches tall, but before they go to seed, turn them into the soil. If they are very large, cut or mow them first.

You can plant your regular garden immediately after turning under your cover crop, but it is best to wait two to three weeks before planting. 

Even small gardens will benefit from the use of cover crops, or "green manures". Tilling, weeding, harvesting and foot traffic of most home gardens tends to destroy soil structure. Planting cover crops is an easy way to revitalize the soil.

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