CORVALLIS, Ore. – Annual cover crops – planted in the late summer and early fall – grow, capture and recycle nutrients that would otherwise be lost by leaching during the winter and early spring. They also protect the surface of the soil from the ravages of winter, including water erosion from downpours and snowmelt as well as wind erosion.
These cover crops help the soil absorb water more readily and they suppress weeds. They also may supply nitrogen and increase organic matter in your garden soil.
If your garden still contains crops (such as broccoli and other cool season vegetables) into November and December, it might be too late to plant cover crops after you harvest them. Instead, plant cover crops around the edges of fall and winter vegetables. Or use mulch to protect the soil.
The Oregon State University Master Gardener handbook, "Sustainable Gardening" recommends planting the following cover crops in the late summer and fall after harvesting your summer vegetables. Mixtures of legumes and non-legumes are especially effective.
- Austrian winter pea – plant in early fall;
- Cereal rye – plant in September or October;
- Winter wheat – plant in September or October;
- Common vetch – plant in early fall;
- Crimson clover – plant in early fall;
- Fava bean – can be planted as late as early November west of the Cascades;
- Annual ryegrass – not good in Willamette Valley and areas with warmer winters, as it tends to self-seed and become a persistent weed.
A free cover crop is the weed chickweed. It forms a dense winter cover, is habitat for early spring beneficial insects and is edible as a salad green.
All these crops are best tilled under in the spring before they flower or set seed, as they become woody and hard to break down upon maturity. Or you can cut them down and compost the tops and till in the bottom of the plants and still get the major benefit of having them.
If you are interested in learning more about cover crops and how they perform in Oregon conditions, you might want to view a copy of OSU Extension's fact sheet "Cover Crops for Home Gardens" (FS 304-e).