Companion Planting – Does it Work?

Companion planting is a method of growing plants together, with the idea that they will benefit each other in some way.

But, just as we have good neighbors, there are bad neighbors as well. Some plants really dislike each other, and shouldn’t be planted in close quarters, as it may cause one to perform poorly or even die. Some of the desirable benefits are:

• Companions improve plant growth – Legumes, for example, benefit their neighbors by enriching the soil with nitrogen.
• Companions help each other grow – Tall plants can provide shade for sun-sensitive shorter plants.
• Companions use garden space efficiently – Vining plants cover the ground, upright plants grow up. Two plants in one patch.
• Companions prevent pest problems – Aromatic plants repel some pests. Other plants can lure pests away from more desirable plants.
• Companions attract beneficial insects – Every successful garden needs plants that attract pollinators.

A lot has been written about traditional plant pairs,  along with a lot of unsubstantiated claims and wishful thinking. There is a wealth of information on its historic use, but there is limited available scientific research on the effectiveness of companion planting. Most information comes from observation, traditional lore, and history.

For example, the Roman naturalist, Pliny, recommended planting chick peas with cabbage to repel the white cabbage butterfly. Roman farmers planted grain between fruit trees and grapevines. Chinese gardeners centuries ago planted beans with their grain crops.

There are some combinations that really work, and others that definitely dislike each other. The following list gives some of the more popular folklore companion pairings that work, or that should be avoided, in a vegetable garden:

• Beans like celery and cucumbers but dislike onions and fennel.
• Beets like bush beans, lettuce, onions, kohlrabi, and most members of the cabbage family, but not pole beans and mustard.
• Cabbage grows better next to celery, dill, onions and potatoes, but dislike being near strawberries, tomatoes, and pole beans.
• Carrots like leaf lettuce, radish, onions and tomatoes, but plant dill at the opposite end of the garden.
• Corn grows well with pumpkins, peas, beans, cucumbers and potatoes, but keep tomatoes away.
• Cucumbers like corn, peas, radishes, beans and sunflowers and dislike aromatic herbs and potatoes.
• Lettuce grows especially well with onions, strawberries carrots, radishes and cucumbers.
• Onions do well near lettuce, beets, strawberries and tomatoes but keep them away from peas and beans.
• Peas like carrots, cucumbers, corn, turnips and radishes, beans, potatoes and aromatic herbs. Keep the peas away from onions, garlic, leek, and shallots.
• Radishes grow well with beets, carrots, spinach and parsnips, cucumbers and beans. Avoid planting radishes near members of the cabbage family.
• Squash likes icicle radishes, cucumbers and corn.
• Tomatoes love carrots, onions and parsley, but keep cabbage and cauliflower away from them.

The opposite side of companion planting is growth suppression. One of the best-known plants that suppresses growth of other plants is the black walnut tree. It produces juglone, a strong toxin that not only retards growth, but also prevents seeds from germinating.

Other plants that have growth-suppressing qualities are eucalyptus, sunflowers, goldenrod, quack grass, and foxtail grass. These plants produce toxins in an attempt to extend their territory, eliminating competition for nutrients, water and sun.

The long tradition of intentionally interplanting indicates that there is truth in the benefits of companion planting. Much of the information you can find about companion planting is based on long-standing traditions, and not supported by actual scientific proof. Your home garden is the best place to conduct your own experiments, and see what actually works for you.

If you decide to try companion planting, set up your plots of planting carefully, and keep records of what you observe. Because weather, soil types, and insect populations are variables that can affect growth, your trials and experiments should be repeated over a period of years. Don’t expect miracles, but instead use companion planting as just one part of your garden management program.