Pole beans require something to climb on and grow upwards. While they do require some basic environmental stimuli such as water, light, and gravity, the key stimulus that encourages their upward growth is touch. When the vine of a pole bean plant comes into contact with a support structure, such as a trellis, stake, or a nearby plant, it wraps its tendrils around it and uses it as support to grow vertically. Without some form of physical contact or touch, pole beans may fail to grow upward and spread out horizontally instead.
