14 Plants You Should Never Grow Side-By-Side

These pairs of plants make decidedly unfriendly garden neighbors.

June 23, 2016
transplanting small squash plant
Melpomene/shutterstock

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. 

scallions and peas
1/7 Rodale Images
Onions + Peas

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.

Related: Onions: A Growing Guide

potatoes and tomatoes
2/7 Rodale Images + Christa Neu
Potatoes + Tomatoes

According to The University of California Master Gardeners, growing tomatoes and potatoes together spells trouble. They’re attacked by the same blights, so when they’re right next to each other, the diseases spread more easily.

peppers and beans
3/7 Rob Cardillo + Rodale Images
Peppers + Beans

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. 

carrots and dill
4/7 Thomas MacDonald
Carrots + Dill

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. 

Related: Your Guide To Growing Carrots

cabbage and grapes
5/7 Rodale Images
Cabbage + Grapes
Folklore says that sowing cabbage seeds near grape vines spells trouble for your homemade wine. According to Rodale’s Successful Organic Gardening: Companion Planting, gardeners noticed this adverse effect some 2,000 years ago. 
walnuts and tomatoes
6/7 Miroslav Hlavko/shutterstock + Christa Neu
Black Walnuts + Tomatoes

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

lettuce and broccoli
7/7 Patrick Montero + Matthew Benson
Lettuce + Broccoli

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

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