Scientists have tested some of this folk wisdom and have found this type of interplanting to be beneficial in several ways. Some plants repel or at least confuse insects pests while others attract beneficial insects that aid pollination or attack the bad bugs. Some plants supply additional nutrients to the soil that affect the growth and flavor of their companion or simply provide them with shade.
Native Americans have long used the method of companion planting called the Three Sisters which groups pole beans, corn, and pumpkins or squash. The pole beans replace the nitrogen the corn consumes while using the cornstalks for support. The corn shades the squash or pumpkins whose prickly vines smother weeds and deter animal predators from feasting on the corn and beans. Here are some other companions at work:
Bear in mind that to have a real effect companion plants need to be grown in sufficient quantity. One summer savory plant at each end of a row of beans isn’t going to be as effective as interspersing them throughout the row and along each side.