Hairy vetch (Vicia villosa), also known as winter vetch is a nitrogen-fixing plant that is used mostly for cover-cropping in monoculture fields. Native to Europe and Asia, it is a winter plant sown in the Fall and, in places where it snows, is killed off with the cold or tilled into fields. When a nitrogen-fixing plant dies or is cut back, roots die and release the nitrogen nodules into the soil. Here is sunny San Diego the vetch thrived since I sowed it in Spring of last year. It is a pretty, vining plant, with lovely dark purple blooms that bees and other pollinators love. It produces pea pods like its edible relative the fava bean, but I wouldn’t eat them. The seeds may be bad browse for livestock as well. The roots help hold soil during winter rains, too.
Vetch can be hard to get rid of because it reseeds easily. It will also climb up bushes, competing with the bush for sunlight. If I didn’t know about the nitrogen-fixing properties and if the bees didn’t like it so much, I’d suspect it of being an invasive.
To control it I take my trusty hand scythe and cut the vetch out of bushes and close to the ground. I leave the vines to decompose and protect seedlings that I plant to take advantage of the newly-enriched soil.
If you don’t want a cover crop that is so aggressive I suggest sowing a mixture of lupine, sweet peas, edible peas and fava beans in the Fall here in Southern California, and again in early Spring. In cold areas check with your farm advisor on when to plant.