Green beans (Phaseolus vulgaris) are also commonly called string beans or snap beans, and they're characterized by their edible seed pods. As their name implies, green bean pods are usually green, but some varieties of the species, commonly called wax beans, produce yellow pods. The pods of some cultivars are purple when raw but turn green when cooked.
Green bean plants are annuals, meaning they die after a single growing season. The plants don't tolerate cold weather and are vulnerable to damage from early spring frosts. They grow best in sunny locations with well-drained soil, and they mature quickly, often bearing tender young pods within 45 to 60 days after planting.
Pole beans come by that name naturally because they have a vining growth habit that requires support from a trellis or pole. Pole bean vines can grow 10 to 15 feet long, and are prolific, producing eight or nine pounds of beans per 10-foot row. Growing pole beans on upright supports makes them easy to harvest.
The 'Kentucky Blue' pole bean cultivar produces pods with a round cross section, the type most common in supermarkets. 'Romano' is a flat-podded variety whose pods have a distinctive nutty flavor.
Green beans are legumes that produce their own nitrogen, and if you give them supplemental nitrogen fertilizer, you'll encourage foliage growth at the expense of development of the beans themselves.
Bush bean varieties remain smaller than pole beans; the plants are self-supporting and don't require staking or trellising. Many gardeners choose bush varieties because of the convenience of their growth habit, but the plants tend to be less productive than pole beans, producing five to six pounds of beans in each 10-foot row. Because they grow closer to the ground, bush beans are also relatively more difficult to harvest than pole beans. Bush beans tend to mature earlier than pole varieties, but they typically produce for a shorter period of time.
Popular green varieties of bush bean include 'Blue Lake' and 'Provider.' 'Golden Wax' is a yellow-podded variety, and 'Royal Burgundy' produces purple pods.
Green beans are susceptible to damage from leaf-eating beetles and caterpillars. Covering bush beans with fabric row covers can keep insects away from the plants. If beetles are attacking the pole beans, you can usually control them effectively by manually picking the beetles from the plants and dropping them in a bucket of soapy water.
Half-runner beans have a vining growth habit similar to that of pole beans, but their vines are much shorter, typically about 3 feet long, and they may be grown without the support of a trellis or pole. The plants may be more productive, however, if they're grown on a support.
Half-runner varieties include 'White Half-Runner' and 'Mountaineer White,' both of which, despite their names, produce light green pods.