Companion planting: what works
Pairings with real evidence, and popular myths to skip
What it is
Companion planting means growing two or more kinds of plants close together on purpose, to help growth or yield or to hold pests back.
Some ideas have good evidence behind them. The popular charts of plant friends and enemies mostly don't, so it pays to know the difference.
Flowers for helpful insects
This is the best-supported idea. Hoverflies, tiny parasitic wasps and other beneficial insects need pollen and nectar, and their young eat aphids and caterpillars.
- Sweet alyssum draws in hoverflies.
- Buckwheat feeds small parasitic wasps.
- Dill, cilantro and basil, left to flower, are favorites too.
- A mix of plants keeps beneficial insects around all season.
Trap crops
A trap crop is a plant a pest likes even more than your crop. In Utah trials, blue hubbard squash planted two weeks before pumpkins drew squash bugs away from the pumpkins. It only works if you deal with the pests on the trap crop.
The marigold myth
French marigolds can reduce root-knot nematodes in the soil, but only when grown as a dense crop. Plant them under 7 inches (18 cm) apart, at least two months before your vegetables. Dotting a few among your crops doesn't work.
Charts of friends and enemies
There's no scientific basis for the long lists of plants that love or hate each other. They're fun, but don't plan your garden by them. In one study, aromatic herbs like mint did little or nothing to keep insects off nearby crops.
The three sisters has real roots. Developed by Native American nations in the Northeast, it grows corn, beans and squash together, with the beans adding nitrogen to the soil.
Easy ways to start
A varied garden is a healthier garden.
- Tuck flowering herbs and flowers among your vegetables.
- Sow quick radishes along with slow carrots; the radishes are pulled before they crowd the carrots.
- Grow shade-tolerant salad greens on the north side of corn or tomatoes.
- Mix plant families instead of planting big blocks of one crop.
Related plant problems
Sources
- University of Maryland Extension: Vegetable Succession and Companion Planting
- Washington State University: The Myth of Companion Plantings
- UF/IFAS Extension: Marigolds (Tagetes spp.) for Nematode Management
- Utah State University Extension: Blue Hubbard Squash as a Trap Crop to Suppress Squash Bugs
General guidance, not a diagnosis. Written by PlantWiz in our own words from the sources above.