What is it: Hairy vetch is a legume that's hardy enough to survive the winters in most US climates, even New England. If allowed to grow long enough, it can add quite a lot of nitrogen to the soil.
Seeding rate and planting tips: Recommended seeding rates for hairy vetch vary widely and can be as low as 15-20 pounds per acre. Hairy vetch can be mixed with winter rye or oat for better erosion control and additional organic matter. Seed hairy vetch at a rate of 30-35 pounds per acre with 40 pounds per acre of oat, if seeded in late July/early August, or with 40 pounds per acre of either winter rye or oat in late August or early September for over-wintering.
Hairy vetch requires rhizobia bacteria to grow and thrive. Rhizobia establish themselves in the roots of legumes as they grow, taking nitrogen from the atmosphere and converting it to a form the plant can use. When planting hairy vetch, it is important to use the correct rhizobia species as an inoculant (the one for all vetches and peas).
Why use it: Hairy vetch is excellent for building soil fertility, as it takes in nitrogen from the air as it grows. When allowed to grow over the winter and into mid-May or later, hairy vetch will add significant amounts of nitrogen to the soil - over 100 pounds per acre!
When to kill it: Mow hairy vetch before it seeds, then till into the ground.