Companion gardening is a practice in which different plants are grown in close proximity to influence crop productivity. Companion planting influences available nutrients, pollination and pest control. According to the University of Arizona, a well-known example of this is the Native American "Three Sisters" planting of squash, corn and beans.
In "Three Sisters" plantings, the corn acts as a trellis for the beans, while the squash leaves cover the ground to prevent weeds. The beans provide nitrogen to the soil. Some plant scientists discount companion planting. However, studies show that the benefits of the intercropping some plants include chemical, physical and biological changes that enhance their survival.