Fresh manure can damage young roots and loses nitrogen easily, as it is leached away in the rain. Composted manure provides slow-release nitrogen for several years. Jessica Paige, of the Washington State University Extension Services, explains that composted manure converts nitrogen to a stable form, releasing 50 percent of nitrogen to the soil the first year. Usable nitrogen is released in lesser amounts in subsequent years. Composted horse manure can be added to soil to improve texture and composition, but it can also be used alone for planting vegetables such as beans.
Place containers filled with composted horse manure, or layer it over the soil, in an area that receives six to eight hours of direct sunlight a day. Composted manure can also be heaped into mounds 4 to 6 inches deep and 12 to 24 inches in diameter.
Sow bean seeds in late spring after all danger of frost has passed in your area, and the soil has warmed. Beans germinate best in soil with temperatures above 60 degrees Fahrenheit, but will germinate at 50 degrees. Lower temperatures delay germination and may cause seeds to rot in the soil before sprouting.
Plant bush bean seeds to a depth of 1 inch, spaced 4 to 6 inches apart. Space pole beans 8 to 10 inches apart and provide a trellis for growing. Cover with soil and firm down with your hands.
Moisten the soil to a depth of 2 inches. Keep soil moist until seedlings emerge in eight to 10 days, depending on soil temperature and weather conditions. Avoid soggy soil as bean seeds rot easily in cool, wet soil.
Water beans deeply once a week, if waterfall is insufficient. Beans require an inch of rain per week. In dry periods, supplemental watering is required. Water to moisten the soil to the root level. Allow soil to dry slightly before watering again.
Harvest beans when pods are 3 to 4 inches long and the thickness of a pencil. Young beans are crisp and tender, but pods toughen as they mature.