Buckwheat is a quick-growing edibile summer annual. Though not a legume, is an excellent cover crop. The seeds germinate quickly, within 3 to 4 days of sowing and when harvested are edbile as a grain. When densely planted it efectively supresses weeds and supports a variety of beneficial insects, including honeybees.
Direct sow after frost.  Scatter the seeds at a rate of one pound per 500 square feet of garden space, then rake them in and water again, or plant roughly half an inch deep and three to four inches apart.