Two main types of beans exist: dry beans and string beans. Dry beans are grown for the protein-rich seeds that store well all winter. Dry beans grow as bush-type plants, but a few semi-vining varieties can be trained to grow on poles in limited space. String beans grow in bush form, harvested about seven weeks after planting, and pole types, which mature at about 10 weeks.
All beans begin their life cycle as seeds, grow into small seedlings, and then into full-grown plants that flower and produce seed pods, containing beans or seeds that are harvested.
String bean seeds can be started indoors around the time of the last frost. To plant string beans directly outdoors, they should be germinated first, by soaking in a glass of warm water for three hours, then rinsing them several times a day until small shoots sprout. Sprinkle the shoots with bean/pea inoculant (Rhizobia nitrogen-fixing bacteria) before planting.
Plant dry bean seeds outdoors two weeks after the last frost, when the soil has warmed completely. Bean seeds require soil temperatures above 60 degrees Fahrenheit for germination. Cover rows with clear plastic to heat soil and aid germination. Remove plastic as soon as seedlings appear.
Seeds sown indoors should be planted in single pots, with a growing mixture of even portions: fine potting soil and sifted, sterile compost. Begin hardening seedlings off for transplanting when they are 3 to 4 inches tall. Plant in the garden after all danger of frost has past. The soil can be covered with black plastic a month prior to planting to help the warming process along.
Beans can be grown in all zones. They like full sun and well drained soil, enriched with compost. Do not fertilize heavily, until after the first harvest, as too much nitrogen will lead to lush foliage, but few seed pods. Beans are shallow rooted and should be kept evenly moist throughout the growing season, especially after flowers have set. String beans with water stress result in small or C-shaped pods. Keep beds weeded, and mulch lightly to conserve moisture. String beans require some support, especially pole varieties.
Pests and Diseases
Bean mosaic causes foliage on dry beans to have yellow patches. Controlling aphids, which spread the viral disease, with floating row covers can protect beans from aphids and other insects that eat their leaves. Other diseases can be prevented from spreading by avoiding working with plants when leaves are wet and mulching walkways to prevent rain from splashing soil with disease spores onto plants.
The major pests for string beans, from mid-season on, are Mexican bean beetles. Prevention entails covering bean plantings with spun-bonded row covers or interplanting with petunias, which deter these pests.
Harvesting Mature Plants
Harvest dry beans late in the season, after most of the leaves have fallen off. If pods did not dry thoroughly while on the plants, they can be bunched together and hung upside down in a warm, dry place to complete the drying process.
String beans can be harvested early, while they are still young or allowed to mature to full size for better flavor. Dry some of the seeds in a cool location and store in a tightly capped jar for planting next year to continue the bean plant life cycle.