Now that we’ve got a little background on why green manures work, what do we do with them?
The Stewardship Gardening team at WSU Extension gives us the how-to.
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.
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 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 and their planting dates:
- • Crimson Clover – Sept-Mid Oct
- • Vetch – Late Aug-Mid Oct
- • Field Peas – Late Aug-October
- • Fava Beans – Late Oct-Early Nov
- • Cereal Rye – Late Sept-Early Oct
- • Winter Wheat – Late Sept-Early Oct
- • Tyfon (“Holland Greens”) – May-Sept
- • Corn Salad – September
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. For a simple, downloadable chart of this planting schedule, including recommendations for spacing and notes on soil preferences, etc., click the link below:
See Part 1 of Green Manures in Your Garden here.