Plants, just like people, have friends and enemies, and they need to be taken into account when planning a vegetable garden. Companion planting, an ancient method of combining and intercropping, provides comprehensive insect control, soil enrichment, and shade protection for a large variety of plants. Companion plants reap the benefits from this mutual friendship in a number of ways.
The "Three Sisters"
The best-known example of companion planting is the "Three Sisters." Native Americans intercropped corn, beans, and squash to take advantage of each plant's beneficial attributes while minimizing growing space. Using this method, plant corn in a mound and surround it with pole beans. Squash encircles the beans. As companions, the corn provides a climbing pole for the beans. In turn, the beans fix nitrogen in the soil for the corn nitrogen and attract beneficial insects. The squash's low-growing leaf canopy minimizes weed growth and in the heat of summer retains soil moisture. Additionally, the squashes' prickly vines repel raccoons that feed on corn and the intermingled crops tend to disorient squash vine borers.
Benefits of Universal Companions
Some companions share their valuable attributes with a large variety of plants. These include basil, borage, carrots, marigolds, nasturtium, and oregano. Benefits include repelling beetles, flies, moths and destructive nematodes; improving the flavor of vegetables; strengthening disease resistance in plants; attracting beneficial insects; and repelling animals such as deer and rabbits.
Soil preferences must be taken into account when arranging companion plants. Always begin with the crop plant and then choose plants that enjoy the same soil conditions. When intercropping, determine plant positioning by averaging the recommended spacing for the two plants. For example, if the main plant's spacing is 10 inches and that of its companion is 4 inches; add the numbers and divide by two for a spacing of 7 inches. Shading must ensure tall varieties do not fully block other plants from the sun. Examples of correct shading are tomatoes providing coverage for peppers and sunflowers protecting bush beans, cucumbers, potatoes, and celery, while also attracting pollinating bees.
Chosen not just for their offensive properties, companions also have the ability to attract beneficial insects and arthropods. Collards can attract diamond back moths away from cabbage and radishes can draw leafminers away from spinach. Ground beetles, lady bugs, praying mantis, spiders, and wasps will eat or infect harmful insects. Drawing bees into the garden increases pollination.
Vegetables and herbs enjoyed as a meal often do well as garden companions. Basil and tomatoes are the perfect example; on the plate and in the garden, basil improves the flavor of tomatoes. Another flavor enhancer for tomatoes is borage; it is also an excellent match for squash and often used to edge strawberry beds. Enhance the flavor of beans by planting them with summer savory. Chamomile improves cabbage and onion flavor while mint improves the flavor of peas, tomatoes, and varieties of the cabbage family.
Certain plants have the ability to improve the soil. Pigweed can help corn and onions by pulling nutrients up from the subsoil. Legumes fix nitrogen in the soil to the benefit of their neighboring plants.