If you've ever read that you must plant basil with tomatoes, or that carrots and onions are best friends, you've encountered companion planting folklore. Most of those pairings come from gardening books and charts, not peer-reviewed research.
We built this hub because gardeners deserve to know what's actually been measured — and what hasn't. Below you'll find the position our planner takes, two university extension sources that say the same thing, the short list of strategies that genuinely improve yields, and an honest, evidence-tagged review of the most popular pairings for each crop we support.
Most companion planting claims are based on anecdotal evidence, not rigorous science. We focus on what reliably works: plant placement by height relative to sun, proper spacing, organic soil amendments, and garden diversity.
The number of rigorous scientific studies regarding companion planting is small compared to the number of books, lists, and charts about companion planting based on anecdotal evidence.
— UMass Amherst Center for Agriculture, Food, and the Environment. See also Montana State University Extension.
Stop guessing at plant pairings. Our garden planner optimizes your layout based on plant height, sun direction, spacing, and your local frost dates — the things that actually make a difference.
Some of it does. General garden diversity reduces pest pressure compared to single-species rows. Legumes (beans, peas) measurably benefit subsequent crops in the same bed by fixing nitrogen. Marigolds suppress soil nematodes, but only when their roots are tilled in as a cover crop — planting them next to tomatoes is not enough. Most popular pairings beyond these have weak or anecdotal evidence.
The lists in popular gardening books are largely inherited from older books, which inherited them from still-older books. Few of the specific pairings have been tested in controlled trials. UMass Amherst Center for Agriculture, Food, and the Environment notes that the number of rigorous studies is small compared to the number of charts and lists in print.
Four things, in roughly this order: plant placement by height and sun direction (tall crops on the north side so they don't shade shorter ones), proper spacing (most reported "bad neighbor" effects are actually competition for light, water, and nutrients), yearly compost top-dressing to restore soil nutrients, and overall garden diversity instead of long monoculture rows.
A few combinations have measurable negative effects, mostly through allelopathy (chemical inhibition) or shared pests and diseases. We flag these as Contradicted in each crop's evidence table. The bigger danger in home gardens is overcrowding — if two plants are too close together, it doesn't matter if folklore calls them friends.
Yes, but the mechanism is physical efficiency, not folklore. Corn provides a vertical pole for beans to climb. Beans fix nitrogen for next season. Squash leaves shade the soil and reduce weed pressure. It's a smart use of one bed's vertical and horizontal space, not a magic combination.
Our planner ignores folklore-only pairings and optimizes layouts based on what actually moves the needle: plant height relative to sun direction, proper spacing per crop, and your local frost dates. You enter your zip code and the crops you want to grow, and we generate a layout that reflects the real science.