Plants That Should Never Be Grown Together

By Growing Home Greens Team · July 31, 2026

Companion planting gets most of its attention for the pairings that help, but the pairings to actively avoid are usually better documented. They come from a specific, identifiable mechanism rather than folklore. A few are worth planning around deliberately.

Onions and beans

Alliums like onion and garlic release compounds that suppress the nitrogen-fixing bacteria living in the root nodules of beans and other legumes. Since that nitrogen-fixing process is the main reason beans get planted near nitrogen-hungry crops in the first place, growing them close together undercuts the exact benefit beans are usually there to provide. Keep them in separate beds or corners.

Tomatoes and corn

Tomatoes and corn share a major pest, the corn earworm (the same insect known as the tomato fruitworm on tomatoes), which means a single infestation can spread through both crops instead of staying contained to one. They’re not directly harmful to each other’s growth the way some pairings are, but planting them side by side raises the odds that one pest problem costs you both crops instead of one.

Tomatoes and brassicas

Tomatoes and brassicas (cabbage, broccoli, cauliflower, kale, and brussels sprouts among them) compete heavily for the same soil resources when planted close together and can stunt each other’s growth, one of the more consistently repeated conflicts across companion-planting references. It’s a resource-competition problem rather than a shared-pest one, so the practical fix is the same either way: separate beds, or several feet of distance within a large one.

Anything in the same family, in the same spot, repeatedly

Beyond specific plant-to-plant conflicts, tomatoes, potatoes, and peppers are all nightshades that share the same soil-borne diseases and pest pressure. Growing any of them in the same bed location year after year builds up those problems in the soil over time even without a second conflicting plant involved. Rotating which bed each family grows in from year to year matters as much as what’s planted beside it in a given season.

Where to check before you plant

Our Garden Designer checks every placement against this data automatically and flags a documented antagonist before you commit to a layout, and each plant’s companion page explains the specific mechanism behind a given conflict rather than just listing a name to avoid. See Companion Planting, Explained for how to weigh a documented conflict like these against the softer, folklore-adjacent pairings that don’t have the same evidence behind them.

As an Amazon Associate we earn from qualifying purchases. Some links on this page also go to other retailers we may earn a commission from as an affiliate, at no extra cost to you. We only recommend products with a genuine consensus of positive, independent reviews. See the sources cited on each item.

Pin this for later

Plants That Should Never Be Grown Together: A handful of vegetable pairings have documented conflicts behind them. Here's what they are and why they matter.

Save to Pinterest