WSU Master Gardener: Stewardship Gardening - Planting and Growing Green Manures

Green Manures / Cover Crops

Planting and growing green manures

Green manures: Cover crops that help you improve your soil

Planting and growing green manures

How Do I Work With Green Manures?

Choose the best plants for the time of year and the situation. Growing a mixture of green manures, for example a grass and a legume, is a good idea. Sow or transplant green manures into a prepared garden soil. Green manures may be planted prior to harvest of many late season crops by undersowing. Lightly cultivate the soil under or between maturing crops and sow the green manure seeds. By the time the crop is out of the way a few weeks later, the green manure will be germinated and growing. Green manures may also be planted between rows of raspberry plants in the fall, providing irrigation is available.

Buckwheat is an outstanding summer green manure crop.

The best time to cultivate the green manures is after most of the plants have started to bloom or are close to heading, but before they go to seed. Waiting too long allows the plants to become woody and will be slower to decompose. Harvesting earlier is fine but the plants will not have reached their maximum amount of stored nutrients and potential organic matter. Use a spade, mower, or string trimmer to chop up the green manures, then either mix them in with the top few inches of soil or rake them up and compost them. If they are removed to be composted, remember that you are removing soil nutrients temporarily and compost will need to be added before planting. If the green manure is turned into the soil, wait until they have decomposed before planting the next crop. This is usually one to three weeks depending on the crop, the soil and the weather.

Suggested Green Manure Crops

Crop	Planting Date	Spacing	Seeds/100 Sqaure Feet	Comments
Crimson Clover	Sept - mid October	Broadcast	1-4 oz.	Legume. Does poorly in poorly drained, acidic, infertile soil. Good for undersowing. Avoid other perennial clovers, such as red clover. Inoculate seed.
Vetch	Late Aug - mid Oct.	Broadcast	5-10 oz	Legume. Soak seeds overnight before sowing. Inoculate seed.
Field Peas	Late Aug -October	Broadcast	10-12 oz	Legume. Does reasonably well in poorly drained or infertile soil. Very hardy. Matures late than crimson clover. Inoculate seed.
Fava Beans	Late Oct- early Nov.	6-8"	12-14 oz	Legume. Soak seeds overnight for quicker germination. Large plants, lots of organic matter, nitrogen for soil. Not very hardy. Inoculate seed.
Cereal Rye	Late Sept- early Oct.	Broadcast or 5" spacing	5-10 oz	Produces lost of biomass. Harder than legumes to chop up. Breaks down more slowly. Roots improve soil structure. Chop before stalks turn brown.
Winter Wheat	Late Sept- Early Oct.	Broadcast or 5" spacing	5-10 oz	Same as rye.
Buckwheat	June - August	Broadcast	5-10 oz	Good summer green manure. Does not need lots of water. Attracts beneficial insects. Not winter hardy.
Tyfon	May- Sept	Broadcast or transplant	0.5 to 1 oz	Cabbage family. Do not follow with other members of cabbage family. Edible greens and roots.
Corn Salad	September	Broadcast	1 oz	Good salad greens in winter. Allow to grow in early spring before chopping.

Other crops may also be used as green manure crops, either alone or in combination with other crops. These include winter and spring oats, winter and spring barley, and triticale.

Back to Green manures: Cover crops that help you improve your soil

More information about this topic is available through your local Cooperative Extension Office.

Adapted by James A. Kropf, Extension Faculty, Horticulture, Small Farms and Farm Marketing. (1998).