   Legumes to Plant in Your Garden - December 8, 2004 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Cover crops are an inexpensive and environmentally friendly way to increase soil nitrogen and organic matter while protecting soil from erosion and occupying space that might otherwise support weeds. Selecting the proper cover crop species requires an assessment of your needs and some trial and error. In this discussion, I’ll assume that your goal is to increase soil nitrogen. However, cover crops can be used for many other purposes (improved soil structure, attracting beneficial organisms, creating mulch, improving water infiltration, etc.). Timing and placement are also critical considerations. What season are parts of your garden fallow and what areas have the greatest needs? Are you planning to grow a crop that requires higher levels of nitrogen such as corn? Consider these factors (and others), then experiment. Keep accurate records of what you’ve done and document the results. Alfalfa has deep taproots that can break up hard soil and bring soil micronutrients to the soil surface. It needs warm soil to germinate and can be planted from spring to late summer (½ oz. seed/100 sq ft). Alfalfa fixes large amounts of nitrogen and does well in alkaline soils. Austrian winter peas can be planted in early spring (3 oz. seed/100 sq ft) and will develop into long vines by early summer. They are moderately cold and drought tolerant and will grow to a height of about 2 feet. Austrian field peas can produce rank growth that can be mowed and composted or turned into the soil as green manure. They are also used for forage, birdseed, and sprouts. Fava beans make an excellent cover crop and are moderately drought tolerant. Some types will fix large amounts of nitrogen in as little as 6 weeks. Use small seeded varieties rather than larger table varieties. Sow 8 inches apart in early spring to late summer. Early spring plantings can be turned under prior to planting warm season vegetables. Fava beans also work well in mountain areas. Hairy Vetch is cold hardy and fixes substantial amounts of nitrogen. After planting in fall (2 ½ oz. seed/100 sq ft), the top grows slowly and root growth continues through the winter. Growth quickens in spring and each plant develops into a vine up to 12 feet long. The stand may reach 3 feet tall and will smother any annual weeds. It should be tilled prior to seeding as it can become a weed. Hairy vetch can satisfy all or most of the nitrogen needs for warm season crops. Woolypod and purple vetch are two subspecies of hairy vetch with similar characteristics. Sweetclovers (annual and biennial), like alfalfa, have a deep taproot that can break up hard soil and bring soil micronutrients to the soil surface. They are moderately cold tolerant when seeded in the fall (1 oz. seed/100 sq ft). They will reach a height of 8 feet if allowed to grow the second year. When starting with cover crops, you may want to select one legume species and plant it in combination with an annual grass. Grasses will produce lots of easily decomposed fibrous roots and take up any excess nitrogen and store it in the leaves until they are incorporated as green manure or composted. Some cool season annual grasses that are suitable as cover crops are cereal rye, annual rye, and winter wheat. Spring grasses include grain crops such as wheat, barley, and oats. If you truly want nitrogen fixation to occur, don’t forget to inoculate the seeds with the appropriate strain of Rhizobium bacteria (see December 1, 2004 Backyard Gardener). If you have been successful with garden cover crops, please let me know. This would be excellent information to share with other gardeners. The University of Arizona Cooperative Extension has publications and information on gardening and pest management. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 ext. 14 or E-mail us at mgardener@verdeonline.com and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://cals.arizona.edu/yavapai/anr/hort/byg/. |