Companion planting: what actually holds up
Last reviewed September 2026 · written from public-domain USDA/NOAA data and Cooperative Extension references — see how we source data
Companion planting ranges from well-supported ecology to charts copied between websites for decades. It is worth knowing which is which before you plan a bed around it.
What the evidence supports
Flowers and flowering herbs (alyssum, dill, cilantro left to bloom, buckwheat) genuinely pull in hoverflies, parasitic wasps and other predators that reduce aphids and caterpillars.
Interplanting and diversity make it harder for specialist pests to find and stay on their host crop, compared with a large single-crop block.
Tall or open crops can shelter shade-tolerant ones — lettuce in the afternoon shade of pole beans or corn.
Legumes fix nitrogen, but most of it becomes available to later crops after the legume dies, not to a neighbor growing at the same time.
What is mostly folklore
Most specific "plant X with Y for better flavor / bigger yield" pairings have little or no controlled evidence. The famous "tomato and basil" pairing is fine to do — they like the same conditions — but basil does not measurably improve the tomatoes.
The classic antagonist claims (beans hate onions, carrots hate dill) are weak. The real reasons to keep some plants apart are competition for light and water, shared diseases within a family, and cross-pollination (dill and carrot, different squash).
A practical layout approach
Group by water and sun needs. Keep members of the same family out of the same square year to year (rotation). Give heavy feeders room for airflow. Edge beds with flowers and let a few herbs bolt for the pollinators. Check the companion planting chart for a specific pair. Do not lose sleep over the charts.