Winter cover crops build garden soils

Last Updated: 
July 24, 2009

CORVALLIS, Ore. – During the summer, as gardens overflow with abundance, it's a good time to remember that they need organic matter replenished every year. Growing winter cover crops is an inexpensive way to let nature do the work.

Often called green manure, cover crops are an effective way to build garden soil during the fall and winter. Certain grains, grasses and legumes grow during the colder months and provide nutrients when spaded or tilled under in the spring. While they grow, cover crops also help reduce soil compaction and prevent erosion. Their roots penetrate and loosen heavy-textured soils, allowing air and water to penetrate.

"Cover crops also are called catch crops," according to Amy Dreves, research associate in the Oregon State University crop and soil science department. "In the rainy parts of Oregon, this is one of the more cost-effective reasons to plant a cover crop. A grass or legume crop catches and uses the nitrogen and other mineral nutrients that winter rains normally leach away."

Nearly all garden soils need organic matter to maintain bacteria, fungi, earthworms and other forms of life needed to make healthy, fertile soil. When you turn under the cover crop in the spring, these nutrients return to the soil, ready for another crop of vegetables.

Over-wintered crops also provide habitat for beneficial insects and help control weeds. Many legume cover crops can add nitrogen to the soil as well.

Plant cover crops from late August until early October where vegetables have been harvested or between rows where vegetables still grow. Annual grasses or grains make a quick, dense cover that will protect soil. Legumes, such as clover or vetch, are not as quick or dense, but are a rich source of nitrogen when chopped into the soil in the spring. A mixture of legumes and grasses is especially effective.

OSU Extension recommends the following. Legumes: Austrian field peas, common vetch, crimson clover and fava beans. Grains: annual ryegrass, barley and winter wheat.

In the spring, cut down or mow cover crops, compost the tops and till the rest into the soil before they flower or set seed. Allow a few weeks for the cover crop residue to break down.

The complete list and when to sow and turn under the crops are available in the publication "Cover Crops for Home Gardens," FS304-E, available online.

Author: Judy Scott
Source: Amy Dreves