University of Illinois Extension

Cover Crops for Vegetable Gardens

Fall is the time to start thinking about cover crops for the vegetable garden, said Maurice Ogutu, a U of I Extension horticulture educator.

“Every year home vegetable gardeners add compost, manures, or other organic materials to their gardens as a source of organic matter,” said Ogutu. “The organic matter is utilized by earthworms, bacteria, fungi, nematodes, and other forms of life in the soil to make healthy fertile soil. Cover is another source of organic matter for home vegetable gardens.

“Cover crop is a crop planted to benefit the soil and any part of it is not harvestable. The cover crop can improve the fertility of the soil by fixing some of the nutrients important in plant growth such as nitrogen and some cover crop can scavenge nutrients left in the soil after harvesting the crop.”

Ogutu said these cover crops are referred to as green manure crops.

“When the cover crop is plowed under then the nutrients are recycled back into the soil,” he explained. “The organic matter added by plowing under cover crop can also improve soil moisture holding capacity in sandy soils and improve drainage in heavy clay soils.”

Some cover crops can be used to attract beneficial insects that control insect pests and these are referred to as trap crops. Many beneficial insect adults tend to feed on pollen hence the cover crops tend to be more attractive at flowering stage. Cover crops can also be planted to reduce soil erosion by runoff and wind and also to protect plants grown in sandy soils from sand blasting.

“Cover crops for home vegetable gardens need to grow quickly and compete with weeds, and they also need to be managed easily in spring and can be easily plowed under,” he noted. “You can select cover crops based on needs in your garden by planting a legume cover crop such as Austrian peas or hairy vetch to fix nitrogen or planting grass cover crops such as winter wheat or grain rye or oats to scavenge left over nutrients from vegetable garden then recycled by plowing under in spring.

“You can also plant a mixture of grass and legume cover crop to get both benefits.”

Cover crops can be planted immediately after harvesting vegetables. They require at least four weeks growing before cold weather that stops growth sets in. Immediately after harvesting vegetables, remove plant debris, and till the garden. Add compost or well-rotted manure at the rate of 20 pounds per 100 square feet or complete fertilizers such as 15-15-15 at the rate of one pound per 100 square feet and incorporated into the soil.

“Prepare a fine seedbed by tilling the soil up to a depth of six inches,” he said. “Plant in moist soil or irrigate the soil to keep it moist enough to germinate seeds.

“Plant large-seeded cover crops such as peas, hairy vetch, wheat, oats, and grain rye in rows that are closely together at the rates one-quarter pounds per 100 square feet. Plant small seeded cover crops such as buckwheat, mustard, and ryegrass by broadcasting and covering with a thin layer of soil at the rates of about 1/6 pounds per 100 square feet. Some cover crops are killed during winter by freezing temperatures, and the hardy types will be dormant during winter.”

The winter-hardy cover crops will resume growth in spring. Mow the cover crop before it goes into seed and till it under as soon as the ground dries up and can be plowed. The cover crop needs to be tilled under 3 to 6 weeks before planting vegetables in spring. Do not plant vegetable seeds or transplants in grounds where the cover crop has freshly been incorporated.

Cover crop seeds can be purchased at local garden centers or can be ordered from out of state seed companies.