• Crownvetch (Coronilla varia) and hairy vetch (Vicia villosa) are both members of the legume family, a family of plants that forms an association with a type of bacteria in their roots that allows them to convert nitrogen from the atmosphere into a form usable by plant roots. Although crownvetch and hairy vetch share this ability, their classification, use and appearance all differ.
  
  

Classification

• Although commonly called crownvetch, crownvetch does not belong to the genus of true vetches, according to the University of Missouri Extension. Hairy vetch, on the other hand, does belong to the vetch genus, Vicia.
  
  

Uses

• Both crownvetch and hairy vetch work well for erosion control on sites such as roadsides and steep banks; in fact, the University of Missouri Extension indicates that erosion control is the most important use of crownvetch. The Penn State College of Agricultural Sciences also suggests that crownvetch -- a perennial legume -- serves well as a living mulch interplanted with crops like corn. Living mulches remain in the field with the crop, controlling weeds, nutrient runoff and soil erosion. Except during drought years, their shallow roots do not compete with the crop. While crownvetch requires mechanical or herbicidal suppression in order to coexist with crops like corn, as the Penn State College of Agricultural Sciences points out, suppression usually requires far less effort than managing a constantly changing palette of weed species invading a field.
  
  Hairy vetch, on the other hand, grows as a winter annual and finds its primary use as a cover crop. Gardeners plant cover crops in the autumn and till them into the soil when ready to plant in the spring. Because legumes like hairy vetch can fix atmospheric nitrogen, tilling them under boosts soil nitrogen levels without having to rely on synthetic nitrogen fertilizers.
  
  

Identification

• Both crownvetch and hairy vetch have pinkish-purple flowers but are otherwise easily distinguished. Crownvetch flowers form in ball-shaped clusters, whereas hairy vetch flowers grow on long stalks. Both vetches have compound leaves, meaning that each leaf actually consists of multiple leaflets. Each crownvetch leaf contains up to 25 small, oval-shaped leaflets. Hairy vetch leaves contain up to 20 narrow leaflets, each up to 1 inch long. Crownvetch can attain a height of 2 feet, whereas hairy vetch grows as a vine that can reach 3 feet in length.
  
  

Planting

• You will typically plant crownvetch in the spring, using 5 to 15 lbs. of seed per acre. Crownvetch spreads via rhizomes, so even a few seedlings can quickly spread to establish a good planting. Hairy vetch can survive cold winters better than any other vetch, according to the Alternative Field Crops Manual published by the Wisconsin and Minnesota Cooperative Extensions, so you should sow 25 to 35 pounds of seed per acre in the fall.