In the past, I mentioned that we plant buckwheat when we finish harvesting part of our garden. I've had several questions since then so I thought I'd give some more details. Maybe you are finishing your peas and have some empty places in your garden.
We purchased a large bag of buckwheat seed from a farm seed dealer. If you don't live in an agriculture area like us, you can purchase buckwheat seed from numerous seed companies.
When an area of our garden is finished harvesting and we don't wish to plant a successive crop, we till the ground and broadcast the buckwheat seed. The seed does not need covered. It sprouts quickly before the weed seeds have a chance to come up.
In about a month, the buckwheat is full size and blossoming. At this point, we rototill the buckwheat into the ground, before it has a chance to go to seed. We usually immediately plant more buckwheat seed. Don't wait for it to go to seed and drop seeds all over the place, unless you wish to have buckwheat growing on that plot of land for some time! Buckwheat stems are hollow and easy to till in. If you don't think your tiller can make it through, you could always mow it off first, then rototill, but we've never had a problem.
The idea is to add the green matter into the soil where it will decompose and add nutriments to the ground. It is sort of a lazy man's way of making compost. Dick Raymond in "The Joy of Gardening" calls it "green manure". In his test gardens, he added no fertilizers, compost, manure or additives of any kind for years but with regular use of green manure crops, his gardens were rich and increased production.
Last year, in the spot we wanted to plant blueberries, we made numerous plantings of buckwheat, tilling and replanting several times to build up the soil. I saw a big improvement in that areas soil this spring.
Besides buckwheat, peas and beans are two other good choices. Legumes such as peas and beans are especially good at adding nitrogen to the soil. I try to plant corn (a heavy nitrogen feeder) where beans or peas were planted the year before. If you have some old seed that you want to get rid of, broadcast it over the area, and rake lightly or rototill just the top inches. They won't be in neat rows but you could probably pick enough beans and peas to enjoy fresh then rototill the plants for the benefit of the soil.
To me, planting a green manure crop is well worth while just for the sake of keeping those end of summer weeds at bay! Though there are numerous options in cover crops. Buckwheat is a fabulous option because it grows quickly in the hot summer weather and very efficiently smothers weeds, while adding to your soil! The cost of a few seeds is certainly cheaper then most other fertilizer or mulch options - unless you have animals!!! I still have much to learn about gardening but this is something simple that has worked very well for the past several years.