Garden cover crops

This being early November, I suspect most of you removed every trace of your summer vegetable garden, leaving the ground virtually bare. Bare soil is undesirable to the home gardener because of the possibility of erosion caused by wind and rain and the leaching of precious nutrients from the soil. The gardener’s remedy is a cover crop. Cover crops are crops which are allowed to grow in the “off season,” covering the bare ground with thick mass of leaves and stems. These crops capture and hold valuable nutrients, preventing them from leaching into the subsoil and being forever lost. Then, in the early spring, this cover crop is tilled under or, in some cases, left intact, both to the benefit of the spring vegetable garden. It is time to be thinking about what type of fall cover crop you would like to use in your garden.

Cover crops are excellent soil builders. They give gardeners several benefits. Most importantly, as mentioned above, they make soil nutrients available either by “catching” soluble nutrients in the soil before they leach away or by, in the case of legumes, producing nitrogen in their roots.

Studies have measured the biomass, the dry weight of above ground plant material, of certain cover crops. The greater the biomass, the greater the level of nutrient availability to ensuing crops. In one study rye, for example, yielded a biomass of 5,600 pounds per acre, crimson clover 4,200 pounds, Austrian winter peas 4,100 pounds, and hairy vetch 3,200 pounds.

The extensive root systems of some cover crops are effective in loosening and aerating the soil, penetrating compacted soils. In a study conducted to determine rooting depths of several cover crops, it was discovered that red clover, lupine, radish, and turnips put down roots 5 to 7 feet deep, common vetch and mustard 3 to 5 feet, and white clover and hairy vetch 1 to 3 feet!

Second, cover crops squeeze out weeds and shade the ground, preventing the germination of many other pesky weeds.

Third, cover crops improve soil structure (tilth). You may recall that in previous articles I have stated that any soil could be improved by the addition of organic matter. Cover crops, when tilled into the soil, add large amounts of organic matter. Some of them even create deep channels in the soil from which the roots of the crops which follow can greatly benefit.

Finally, cover crops act as a protective blanket for the soil, preventing erosion by wind and rain. This is most important to our farmers but is beneficial to gardeners as well.

The following are descriptions of some of the most common cover crops.

A favorite of many is rye grain, or winter rye (Secale cereale). Rye is a very popular cover crop for gardeners because of its cold hardiness and heavy dry matter production. Rye will germinate at 33 degrees F, grows rapidly at temperatures between 40 and 65 degrees, and can even tolerate temps as low as -40 degrees F! Sow rye at the rate of 2 ½ to 4 pounds per 1,000 square feet. Planting at least four weeks before the first fall killing frost allows it to get a fast start so that it can cover the soil well. Allow at least two weeks between plowing under time and spring planting to allow time for complete decomposition.

Annual ryegrass (Lolium multiflorum) is another good fall cover crop. It germinates readily at 45 degrees F and grows best at temps between 45 and 75 degrees F. Ryegrass is a totally different plant from rye grain, and since its roots are slower to rot, it should be tilled in earlier than rye. Be careful not to let annual ryegrass go to seed, or it may become a weed. Sow at the same rate as rye grain.

Wheat (Triticum aestivum) performs much like rye, except that it prefers 40 degree temperatures for germination and 45 to 85 degrees for optimum growth. Treat wheat much like rye grain, sowing it at rates of between 2 ½ to 4 pounds per 1,000 square feet and tilling it under at least two weeks before planting in the spring.

Crimson clover is a nitrogen-fixing legume and thus helps to build rich soils. It also attracts beneficials, is quite attractive, and helps build good soil structure. Clover can be mixed with wheat or oats and broadcast across the entire garden. The small grains will germinate quickly and act as a nurse crop for the slower germinating clover. Broadcast clover at 20-30 lbs. per acre.

Cover crops are very useful tools for the home gardener who wishes to improve his soil’s structure and fertility. These benefits translate into bigger, healthier, and better-tasting vegetables. Try some cover crops this fall. You’ll be glad you did!

Tim Lewis is a Georgia Green Industry Association Certified Plant Professional, gardening writer, and former Perry High School horticulture instructor. He and his wife, Susan, own and operate Lewis Farms Nursery located on Georgia Hwy 26 two miles east of Elko, where he was born and raised. He can be reached at (478)954-1507, timlewis1@windstream.net, and at LewisFarmsNursery.com.