Companion Planting Checker
Select two or more plants to find out if they're good neighbors, neutral, or best kept apart.
What Is Companion Planting?
Companion planting is the practice of growing certain plants near each other for mutual benefit. Some plants attract beneficial insects that protect their neighbors. Others repel pests, improve soil nutrients, or provide physical support (like corn stalks supporting bean vines).
On the flip side, some plants inhibit each other's growth through chemical compounds released from their roots or leaves (allelopathy), compete for the same nutrients, or attract pests that harm their neighbors.
How Our Checker Works
We maintain a database of companion and antagonist relationships for each plant, compiled from university extension research, established gardening references, and generations of gardening observation. When you select two plants, we check if either plant lists the other as a companion or antagonist.
If neither plant lists the other in either category, the relationship is neutral — meaning there's no strong evidence of benefit or harm from planting them together.
The Classic Companions
Some companion planting combinations are time-tested favorites. Tomatoes and basil are the most famous — basil may repel certain tomato pests and many gardeners swear the flavor of both improves when grown together. The "Three Sisters" combination of corn, beans, and squash has been used by Indigenous peoples for centuries: corn provides a trellis for beans, beans fix nitrogen in the soil for corn, and squash shades the ground to retain moisture.
Marigolds are the universal companion — their strong scent repels many common garden pests, and their roots release chemicals that suppress harmful nematodes in the soil. Plant them throughout your vegetable garden for broad pest protection.
Common Antagonists
Fennel is one of the most antisocial garden plants — it inhibits the growth of most vegetables and should be planted away from your main garden beds. Onions and garlic can stunt the growth of beans and peas. Tomatoes and brassicas (broccoli, cabbage, cauliflower) compete for the same nutrients and can attract each other's pests.
Frequently Asked Questions
Some companion planting relationships have strong scientific support — for example, marigolds' nematode-suppressing effect has been demonstrated in controlled studies, and nitrogen fixation by legumes is well-established science. Other relationships are based on centuries of gardening observation but haven't been rigorously tested in controlled experiments. We include relationships that are widely accepted in the gardening community and supported by extension service recommendations.
A neutral result means we don't have evidence of a strong positive or negative relationship between those two plants. They should be fine planted near each other, but you're unlikely to see specific companion benefits. Most plant combinations are neutral.
You can — companion planting guidelines are recommendations, not hard rules. Many gardeners successfully grow "antagonistic" plants near each other, especially in small gardens where space is limited. The antagonist relationship means those plants may not perform at their absolute best when planted together, but it's unlikely to cause complete crop failure.
Last reviewed: March 29, 2026