Companion planting is the organic practice of mixing a variety of plants together to the benefit of the group. Certain plants improve soil composition, while others may deter pests, and still others attract beneficial insects. In companion planting, plants are mixed throughout the garden as opposed to planting just one single crop within one bed or area. The proximity of the different plants to one another is the tenet of companion planting.
In Native American culture, the practice of planting corn, beans and squash together is an example of companion planting. The beans fix nitrogen in the soil. The corn requires high concentrations of nitrogen. In turn, the corn provides a support for the beans as they grow; they twine around the corn stalks. The squash grows along the ground, providing shade for the soil to retain moisture and reduce weeds.
That the crops are mixed also works to prevent, or at least reduce, the incidence of diseases ruining entire crops. The Great Potato Famine experienced in Ireland in the 19th century is an example of the dangers of monoculture, or the planting of a single crop. Once the blight infected one field, it spread to others because there was nothing to stop it. As long as there were potatoes, the blight flourished.
Companion planting, or intercropping, offers pest control in agricultural applications and in backyard gardens. If you plant your tomato plants all together with no other plants in the bed, the plants are at risk for aphids, tomato hookworm, nematodes, whitefly and other crop-damaging pests. Plant marigolds, onion and garlic bulbs, and mints along with your tomatoes to deter these pests from your tomato plants.
Pest control is one benefit of companion planting. While companion planting provides a deterrent to pests, it also encourages beneficial insects to visit such as butterflies and wasps. Attract hoverflies to your garden with flowering nasturtium, calendula and poppies. Hoverflies eat aphids. Thyme attracts bees for pollination and rosemary attracts both bees and ladybugs. The ladybugs control the aphids.
An additional benefit of companion planting is flavor enhancement. Basil planted with tomato enhances the flavor of the tomato. Summer savory intensifies the flavor of beans, and oregano encourages the beans to grow.
The practice of companion planting also allows you to design your garden so that larger, stronger plants can protect smaller, more delicate plants. For example, okra plants can grow as tall as 6 feet and have thick, sturdy stems and branches. These can act as a windbreak for the more delicate sweet pepper plants in your garden.