July 26, 2014
Certain combinations protect against pests or provide essential nutrients.
A good friend tells you the truth, makes you laugh and has your back. In the plant world, there are friendships, too, although, of course, they are different in nature. Groups of plants that grow well together are called "companions." Companion planting means putting plants together that can be helpful in some way, whether by discouraging insect pests, attracting beneficial insects, providing nutrients or simply offering support.
Many of these combinations come to us through folklore. Some aspects of companionship are true and some are not based on reproducible scientific research. One of the classic companion plantings is the "Three Sisters," in which corn, squash and beans are planted in the same hill. Native Americans developed this combination to get their basic nutrition from a limited amount of space. The cornstalks provide support for the bean plants to grow upward and the beans shade the young ears from burning and repel squash vine borers. The prickly stemmed squash at the base of the corn stalk shades out any potential weeds and discourages some critters. The shaded cornstalk roots are kept moister and cooler.
Another classic combination based mainly on folklore is marigolds with tomatoes. While it is true that the marigold roots emit a substance that is poisonous to many of the soil-dwelling roundworm pests called nematodes, marigolds actually attract whiteflies that could be damaging to tomato plants.
As cited in Cornell University's Department of Horticulture, destructive insects often locate their food by smell. Many plants, especially culinary herbs, produce strong scents that may confuse pests looking for a host to feed on. If you plant aromatic herbs like basil, mint, rosemary, summer savory or catnip among your flowers or vegetables, pests may be confused by the scent and unable to find their target. Other fragrant plants like garlic, onion and chives can be interplanted with vegetables to discourage pest damage to neighboring edibles.
There are some insects and arachnids you can welcome to visit your garden. Beneficial insects like ladybugs, most wasps and spiders, and some beetles will devour pests like aphids. You can use companion planting to attract these beneficials by having a variety of flowering plants that bloom in succession such as coriander, dill, parsley and buckwheat.
Another type of companion planting can occur when tall, fast-growing plants offer protection to low, shade-loving plants. This type of planting works well if you have a delicate shade-loving vegetable such as red leaf lettuce. This is not just for the vegetable garden, but can work well for ornamental plants as well. Sometimes you just want a beautiful hellebore but don't have the right spot of shade. If you plant it under another tall plant with arching foliage you can have your delicate flowers right in the middle of an otherwise sunny garden.
Not all friendships are good. There are a few that it is best to avoid. The same worm attacks tomatoes and corn, so planting them together actually creates a monoculture that can increase the chances of attack. The same holds true for tomatoes and potatoes. They are vulnerable to the same blight, so it is best to grow them away from each other.
As you can see, companion planting encourages an approach that can yield you a less-regimented, even topsy-turvy looking garden. Instead of neat rows of a single crop inhabiting a planting box, you will have community of plants, many of them with abundant flowers, interplanted in glorious harmony and friendship and buzzing with beneficial insects. It is worth a little effort to look a little messy.