Companion planting is the practice of growing crops that are natural allies side-by-side. It’s a tradition based on many years of observations by dedicated gardeners, though in a few cases science backs up the practice, too. The most famous example of companion planting is the “Three Sisters” that Native American farmers planted together—squash, corn, and beans. The three vegetables grow together perfectly: The corn acts as a trellis for the beans, the beans return nutrients to the soil, and the broad leaves of the squash literally “squash” down weeds while locking moisture into the soil, explains The University of California Master Gardeners. But what about plants that are natural enemies in the vegetable garden? Here are seven combinations companion planters say are no-gos.
Traditional wisdom says you should never __plant members of the onion family—including shallots and garlic—with peas. According to the Farmer’s Almanac, companion planters believe the onions can stunt peas’ (and beans’) growth.
According to Rodale’s Successful Organic Gardening: Companion Planting, peppers and beans are both susceptible to anthracnose, so if one gets it, they’ll both wind up infected when planted side-by-side. This disease ruins fruits by causing dark, soft spots to appear.
Dill and carrots are traditionally cast as enemies, according to Good Neighbors: Companion Planting For Gardeners, though no scientific research yet supports this observation by gardeners.
Black walnut trees are notorious for being bad neighbors. According to the National Gardening Association, the trees’ roots emit a chemical called juglone, which is toxic to many deep-rooted plants growing nearby, such as tomatoes. If your yard is loaded with the trees, you’re probably better off growing in container gardens or raised beds.
Research shows that lettuce is sensitive to chemicals found in residues left behind by broccoli plants. Sowing lettuce near broccoli—or in the spot where it used to grow—may hinder seed germination and growth, says Good Neighbors: Companion Planting For Gardeners.