Many of us have planted winter cover crops in our gardens to enrich the soil. Fava beans, winter peas, vetch, and other legumes can do a great job of adding nitrogen to our soils. With a symbiotic relationship with special microorganisms, legumes can take nitrogen in our air and put it into nodules on their roots in a form that's useful to plants.
To get the maximum amount of nitrogen from a legume crop, cut or mow it after it starts flowering in the spring and before seed production begins. The best timing is to do this when 50% to 60% of the plants have developed flower heads. For most of us, this is in late February or March. Cut the plants as close to the soil as you can, leaving the roots (and the attached nitrogen nodules) to decompose.
The top growth can be cut into small pieces, either by hand or with a chipper machine. This material can be added to your compost pile or placed in a layer on the soil. You can also add a layer of compost on top and then cover the compost with burlap bags to keep it moist (by rain or irrigation if there's no rain). This will speed the breakdown of the cover crop debris.
After about 4 weeks, remove the burlap and you're ready to plant new seedlings for your summer crop. If any of the cover crop material is still there, simply move it aside when you plant your seedlings. The cover crop debris can serve as a mulch as it continues to decompose.
For more information on growing cover crops, see this previous blog post: https://ccmg.ucanr.edu/our-blog/?blogpost=55214&blogasset=12496
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