Garden Cover Crops
Seeds are sown into vegetable garden soil—typically in the fall—to preserve and enhance the soil over the winter. They provide a host of benefits:
Prevent soil erosion and compete with weeds in winter when the soil is not being cultivated.
Improve soil porosity and tilth (the physical condition of the soil)
Add large amounts of organic matter to the soil when the lush growth of green, immature crop is tilled under in early spring. Nutrients (nitrogen, phosphorous, potassium, calcium, etc.) are returned to the soil. Cover crops planted primarily for nutrients are known as “green manures.”
Legumes are host to nitrogen-fixation bacteria which extract nitrogen from the air and store it. When turned under, the nitrogen is returned to the soil.
After produce is harvested, till the plant residue into the soil where it will decompose to produce more humus. This prepares the soil for the seed. Use a drop spreader, a broadcast spreader or broadcast seed by hand. For better coverage, make two seeding passes over the garden at right angles to each other. Lightly rake the seed into the top 1/4 inch of soil. The seed must be covered and be in firm contact with the soil for best germination.
Nitrogen fixers. Legumes benefit from use of a seed inoculant when planting.
Large-seeded legume, very good for building tilth and adding organic matter to the soil. Perfect if you’re getting a late start planting your cover crop and/or planning to wait until late spring to plant your garden. Peas like well drained and fertile loam soils.
Planting time: late Sept. to mid Nov. Recommended Seeding Rate: 1 lb. per 200 sq. ft.
Crimson Clover (An Annual Clover)
Colorful and versatile, crimson clover grows readily on both sandy and clay type soils (best with good drainage) and can be used as either a summer or winter cover crop. The dense mass of hairy stems and leaves is very effective against weeds, and will return a large amount of organic matter and nutrients to the soil.
Planting time: late Sept. to mid Oct. Recommended Seeding Rate: 1 lb. per 1000 sq. ft.
Faba Beans (aka Fava Beans)
Earliest of the green manures to mature, allowing you to till them under in mid to late April and get a head start for spring. Its deep taproots help break up clay or compacted soil as well as add nitrogen and humus. Some may experience an allergic reaction to pollen from faba bean blooms.
Planting time: late Sept. to mid Nov. Recommended Seeding Rate: 1 lb. per 100 sq. ft.
Less winter-hardy than hairy vetch, common vetch is best adapted to well-drained, fertile soils. It is not tolerant of wet soils. It is often seeded with a small grain, such as rye. Vetches are annual, vine-type legumes with leaves ending in tendrils.
Recommended Seeding Rate: 1 pound per 400 square feet
Add minimal nitrogen, but are the best tilth builders and quick erosion control.
The perfect tilth builder. And perhaps the most popular cover crop for erosion control because it germinates quickly and grows rapidly in cool weather. Also very hardy.
Planting time: August to early Nov. Recommended Seeding Rate: 1 lb. per 250 sq. ft.
Another great tilth builder and the best summer cover crop.
Planting time: March to July. Recommended Seeding Rate: 1 lb. per 1000 sq. ft.
Gardenway Cover Crop Blend
The most complete Northwest cover crop blend! This mix combines the great growing characteristics of all the major green manure crops suitable for our climate and soils west of the Cascades. Ingredients: 30% Cereal Rye, 27% Austrian Peas, 29% Triticale, 5% Common Vetch, 5% Annual Rye Grass, 2% Crimson Clover.
Planting time: mid Sept. to late Oct. Recommended seeding rate: 1 lb. per 500 sq. ft.