The common bean, Phaseolus vulgaris, is a widely cultivated plant. Whether this plant climbs depends entirely on the specific variety being grown. While all beans fix atmospheric nitrogen into the soil, their physical growth habits differ dramatically. Understanding this difference is important for any gardener planning a successful harvest.
The Critical Distinction: Bush and Pole Varieties
The two main growth habits of green beans are classified by their physical structure and resulting yield pattern. Bush beans exhibit a determinate growth habit, meaning their main stem and branches terminate in a flower cluster, halting further vertical growth. This results in a compact, self-supporting plant that typically reaches a maximum height of two to three feet. The entire crop from a bush bean plant matures relatively quickly, often within 50 to 60 days, providing a single, concentrated harvest.
In contrast, pole beans display an indeterminate growth habit, where the main stem continues to produce vegetative growth and flowers throughout the growing season. These plants develop into vigorous, vining structures that can easily reach heights of 10 to 15 feet under ideal conditions. Pole beans take slightly longer to begin producing, typically requiring 60 to 70 days until the first harvest. This prolonged production period offers a significant advantage, as pole varieties yield a greater quantity of beans per square foot over the entire season.
The difference in stature also influences plant health. Bush beans grow close together in dense rows, which can trap moisture and increase their susceptibility to various fungal diseases. Pole beans, by growing vertically, benefit from better air circulation, which allows their foliage to dry more quickly after rain or irrigation. The choice between the two types often comes down to the available space, as bush beans suit smaller areas, while pole beans maximize yield through vertical expansion.
How Pole Beans Achieve Vertical Growth
Pole beans climb due to a specialized biological mechanism known as twining, which involves a searching movement called circumnutation. The vining stem does not produce true tendrils; instead, the growing tip performs a helical, sweeping motion. This circular movement is the plant’s way of exploring the environment to locate a vertical support structure.
Once the searching stem tip makes physical contact with a suitable object, a touch-sensitive growth response called thigmotropism is initiated. This contact triggers cells opposite the contact point to elongate rapidly, causing the vine to wrap tightly around the support. The bean vine continues to spiral upward, relying on the support structure’s strength to prioritize vertical growth and maximize light exposure.
Essential Support Structures for Climbing Beans
Because pole beans possess a weak stem structure, providing a sturdy support system is necessary for maximizing production and managing the vine’s considerable weight. A variety of structures can be utilized, including single vertical poles, A-frames, and trellises. A simple teepee, constructed by tying together three to five poles at the top, is a popular and structurally sound option that provides multiple climbing surfaces. These supports must be robust enough to hold the weight of a mature, heavily-laden plant.
The ideal height for a pole bean support is between six and eight feet, although some vigorous varieties may exceed this range. When constructing any support, the climbing material, such as a pole or string, should not be too thick; the bean vine struggles to twine effectively around supports wider than about three centimeters. Crucially, the chosen structure must be installed into the ground before or immediately at the time of planting to prevent disruption to the delicate young seedlings.