How Companion Planting Works
Companion planting is the old practice of deciding which crops to grow next to each other and which to keep apart. Some pairings are documented in extension publications and seed catalogs — basil set near tomatoes, whose strong aromatic oils are often credited with masking the crop from pests; carrots interplanted with onions, where each is said to confuse the other's specialist flies. Others are about competition or chemistry: black walnut trees release juglone, which suppresses many vegetables, and brassicas planted beside strawberries are a long-standing example of a pairing that tends to disappoint.
Not every traditional claim holds up to controlled study, and we don't pretend otherwise. What this tool does is surface the relationships that are widely cited in the sources our crop database is built on, so you can plan around them. It reports what the data says — "these two are listed as companions" — rather than inventing specific horticultural benefits the data can't back up.
What Counts as a Companion
In our crop database, a companion means two crops are documented to grow well together in university extension publications or Johnny's Selected Seeds charts. An antagonist means documented incompatibility — competition for resources, a shared disease or pest, or an allelopathic effect where one plant chemically suppresses the other. Everything else is neutral: most crop pairings have no documented relationship in either direction, and that is the default, expected state. The relationship matrix only colors in the companion and antagonist cells so the actionable information stands out.
How to Use the Tool
Select the four to eight crops you're planning to grow this season and check the relationships. Read the warnings list first — those antagonist pairings are the things you actually need to act on. Lean into the recommended companion pairings where you can, and if your selection contains antagonists, use the suggested bed layout to plan physical separation across two or three beds. For the full per-crop growing details, browse the vegetable growing database.
Frequently Asked Questions
What is companion planting?
Companion planting is the practice of growing certain crops near one another because the pairing is thought to benefit one or both plants — through pest confusion, improved pollination, better use of space, or simple compatibility. It also covers the reverse: keeping crops apart when one is known to compete with, shade out, or attract pests to the other.
Does companion planting actually work?
Some of it is well documented and some of it is traditional folklore. The relationships in this tool are drawn from university extension publications and seed-catalog charts, where they are widely cited — but not every traditional claim has been rigorously tested in controlled trials. Treat the documented pairings as a sensible starting point for planning, not as a guarantee. We deliberately don't fabricate specific benefits the data doesn't support.
Why are some plants listed as antagonists?
An antagonist pairing means two crops are documented to grow poorly together. The reasons vary: direct competition for nutrients, water, or light; allelopathy, where one plant releases compounds that suppress another; shared pests or diseases that spread more easily when the crops are adjacent; or one plant attracting pests that then move to its neighbor.
Can I just plant everything together?
For the most part, yes — the large majority of crop pairings are neutral, with no documented relationship in either direction. Only the specific combinations the tool flags as companions or antagonists are worth acting on. The matrix leaves neutral pairings blank on purpose, so your attention goes straight to the combinations that actually matter.