Companion planting is an organic gardening concept that recognizes the beneficial effects certain plants can have on others when planted close together in a garden. These positive effects include healthier and more rapid growth, and enhanced flavor of the fruit. Plants can play a major role in keeping harmful pests from damaging other plants, either through attracting beneficial insects that consume these pests, or through having chemical properties that deter pests. Flowers, herbs and vegetables all have been discovered to exhibit these amazing properties.
Corn, Beans and Squash
Native Americans understood the compatible qualities of these vegetable staples. Corn is a tall plant that acts as a trellis for the climbing bean plant vines. Beans capture nitrogen from the air and return it to the soil when their growing season is over and they decompose. Corn is a heavy consumer of nitrogen. Squash plants grow densely, almost like ground cover, and crowd out weeds that could take away water and nutrients from the beans and corn. Pumpkin plants can perform this same function. Beans attract beneficial insects that attack leafhoppers and other pests harmful to corn. An added benefit of this grouping is that together they form a kind of balanced diet.
Radishes for Pest Control
Radishes are effective at pest control for a variety of other vegetables. Radishes lure leafminers away from tender spinach leaves by substituting their own leaves on the bugs' menu. The radishes grow underground, so they are not harmed. Radishes and squash are good companions; radishes deter squash borers. They may also keep cucumber beetles away.
Plants That Attract Beneficial Insects
Insects that prey on harmful garden pests include wasps, ground beetles, lady bugs, spiders and even some species of flies. Plants that have a strong fragrance such as parsley, coriander, dill, carrots and parsnips are able to attract these to the garden and protect other vegetables nearby from pests such as aphids and caterpillars.
Rosemary for Pest Control
Rosemary is an extremely fragrant herb that drives away cabbage moths, carrot flies and bean beetles. Cuttings of this herb placed near the crowns of carrot plants are very effective at this natural pest control.
Taller Plants for Shade
Leaf lettuce is an example of a vegetable that prefers partial shade, and does not grow as well when the days turn from cool to warm to very warm in the late spring. Okra is a good companion plant for shade and can provide wind protection for pepper plants as well. Spinach likes the shade provided by peas and beans.
Borage, Alfalfa and Beets for Soil Quality
Borage adds delicate blue flowers to the garden, but also deters hornworms from attacking tomatoes. Gardeners have found that borage boosts both the crop yield and flavor of strawberry plants. Borage adds important trace mineral elements to the soil after decomposing, including potassium and calcium. Alfalfa can help build iron, phosphorous, and magnesium levels in the soil. Like beans, alfalfa also takes nitrogen from the air and puts it into the soil. Beets contribute magnesium to a vegetable garden.