Companion planting is a gardening concept that takes advantage of the fact that some plants are mutually beneficial to each other. Rather than planting garden and yard plants in neat homogenous rows, companion planting consists of different types of plants grown interspersed with each other.
Three sisters gardening is an example of companion planting used by Indians in North America. Corn, Beans, and Squash (the three sisters) are planted together, often in the same hole. As the plants grow the corn supports the beans, the squash leaves keep the soil moist, and the beans deter certain pests.
Another common combination is peas, carrots, lettuce, and radishes. The peas fix nitrogen into the soil, the radishes loosen the dirt so the carrots have room to grow after radish harvest, and the lettuce keeps the soil moist and the weeds down.
Some plants are used in companion planting for their pest deterring capabilities. Onions and garlic are well known for their bug repellant characateristics and should be planted amoung almost all garden plants. The one notable exception is peas, as onions seem to hinder pea plant growth. Marigolds also repel some garden pests and also make the garden attractive. Some herbs such as thyme and rosemary can be planted among other garden plants to help keep the bugs away.