Companion planting chart, graded by evidence
Much companion-planting advice is tradition with little testing behind it. This chart lists pairings with a source we could read and labels each one: tested in studies, practical, traditional or not supported.
18 pairings
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Tested in studies
Tomatoes with Basil
Fewer thrips
A few field and greenhouse studies found fewer thrips on tomatoes grown with basil, and basil may even help tomato growth.
Source: UMN Extension
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Tested in studies
Tomatoes with French marigolds
Fewer thrips and whiteflies Includes a glasshouse study
Marigolds reduced thrips on tomatoes in some studies, and in a glasshouse trial French marigolds kept whiteflies off tomatoes through the limonene they release.
Source: UMN Extension; Conboy et al. 2019
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Tested in studies
Cabbage family with Arugula, mustard, rapeseed or napa cabbage
Trap crop for flea beetles
These spicier relatives draw flea beetles away from the main crop. Mixing three or more trap species worked better than any one alone.
Source: UMN Extension; Parker et al. 2016
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Tested in studies
Brussels sprouts with Sage or thyme
Fewer diamondback moths Greenhouse study
Sage and thyme reduced diamondback moth egg-laying on Brussels sprouts in a greenhouse.
Source: UMN Extension; Dover 1986
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Tested in studies
Broccoli with Thyme, onion or nasturtium
Less caterpillar damage One-season farm trial
In an Iowa trial, thyme, onion and nasturtium reduced damage from cabbage loopers and imported cabbageworms on broccoli.
Source: UMN Extension; Riesselman, Iowa State
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Tested in studies
Cabbage with Marigold, onion or nasturtium
Fewer cabbage worms One-season farm trial
The same Iowa trial found marigold, onion and nasturtium reduced both caterpillars on cabbage.
Source: UMN Extension; Riesselman, Iowa State
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Tested in studies
Squash and pumpkins with Nasturtium
Fewer squash bugs
An old practice that research supports: nasturtium can reduce squash bug numbers. In Iowa, nasturtium and marigolds both cut squash bug and cucumber beetle damage.
Source: UMN Extension; Riesselman, Iowa State
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Tested in studies
Squash, pumpkins and cucumbers with Blue Hubbard squash
Trap crop
Blue Hubbard squash attracts cucumber beetles, squash bugs and squash vine borers, pulling them away from your other squash-family crops.
Source: UMN Extension
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Tested in studies
Squash with African marigold and sweet alyssum
More aphid predators
In a Florida study these flowers increased the natural enemies of aphids and had a slightly positive effect on yield.
Source: UMN Extension
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Tested in studies
Sweet corn with Buckwheat, cowpea or sunn hemp
More corn earworm predators
Flowering plants grown with sweet corn increased the predators and parasitoids of corn earworm.
Source: UMN Extension; Manandhar & Wright 2016
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Tested in studies
Any crop with aphids with Plenty of flowers
Hoverflies against aphids
Hoverfly (syrphid) larvae eat large numbers of aphids. The adults visit a wide range of flowers and lay eggs nearby.
Source: UMN Extension
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Practical
Carrots with Radishes
Saving space
Sown side by side, fast radishes are pulled long before slow carrots need the room.
Source: UMN Extension
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Practical
Tomatoes or peppers with Early lettuce, spinach or basil
Two crops from one bed
Grow a quick crop early, then set tomatoes or peppers into the same bed as it finishes. The later crop's leaves fill in as the first is harvested, which also shades out weeds.
Source: UMN Extension
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Practical
Sweet corn with Cowpeas sown underneath
Soil health
Legumes fix nitrogen from the air, reducing fertiliser needs; a cowpea cover crop can grow under sweet corn.
Source: UMN Extension
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Practical
Squash and pumpkins with Flowers all season
Better pollination
Squash needs insects to pollinate it. Steady flowers and habitat support bumblebees and other pollinators.
Source: UMN Extension
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Traditional
Corn, beans and squash with Each other (the Three Sisters)
Mutual support
Corn gives beans a pole to climb, beans add nitrogen, and squash may deter raccoons from the corn. Used by Indigenous peoples for hundreds of years and still the base of milpa farming in Mesoamerica.
Source: UMN Extension
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Not supported
Potatoes with Marigolds
Repel Colorado potato beetles
Often recommended, but multiple studies found marigolds do not deter Colorado potato beetles.
Source: UMN Extension; Moreau et al. 2006
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Not supported
Cabbage family with Marigolds or green onions
Repel flea beetles
Listed on many gardening sites, but there is little research behind it and some studies contradict it. Use a trap crop instead.
Source: UMN Extension
How honest is companion planting?
Charts of plant "friends" and "enemies" are everywhere, but University of Minnesota Extension notes that such lists "are not always accurate or backed by research". The best-supported pairings work in a few clear ways: a trap crop that pests prefer, flowers that feed the insects that eat pests, strong smells that confuse pests, and plain good use of space and soil. Even tested pairings are not guarantees; many studies covered one site, one season or a greenhouse, and results vary with weather and pest pressure.
How to use the chart
Choose a crop to see its pairings, and untick evidence levels to narrow the list. Each card names the crop, its companion, the purpose and what was found, with the source. The full references are listed below.
Sources
- Hoidal N. Companion planting in home gardens. University of Minnesota Extension. extension.umn.edu
- Conboy NJA, McDaniel T, Ormerod A, et al. Companion planting with French marigolds protects tomato plants from glasshouse whiteflies through the emission of airborne limonene. PLOS ONE 2019;14(3):e0213071. doi:10.1371/journal.pone.0213071
- Parker JE, Crowder DW, Eigenbrode SD, Snyder WE. Trap crop diversity enhances crop yield. Agriculture, Ecosystems & Environment 2016;232:254–262. doi:10.1016/j.agee.2016.08.011
- Dover JW. The effect of labiate herbs and white clover on Plutella xylostella oviposition. Entomologia Experimentalis et Applicata 1986;42(3):243–247. doi:10.1111/j.1570-7458.1986.tb01029.x
- Riesselman LB. Companion Planting: A Method for Sustainable Pest Control. Iowa State University Research and Demonstration Farms Progress Report ISRF09-12, 2010. dr.lib.iastate.edu
- Manandhar R, Wright MG. Effects of interplanting flowering plants on the biological control of corn earworm and thrips in sweet corn. Journal of Economic Entomology 2016;109(1):113–119. doi:10.1093/jee/tov306
- Moreau TL, Warman PR, Hoyle J. An evaluation of companion planting and botanical extracts as alternative pest controls for the Colorado potato beetle. Biological Agriculture & Horticulture 2006;23(4):351–370. doi:10.1080/01448765.2006.9755336
Questions
Do marigolds keep pests away?
Sometimes. Studies found marigolds helped against thrips and whiteflies on tomatoes and squash bugs on squash, but they do not deter Colorado potato beetles.
Are there plants that should never grow together?
Many charts list "enemies", such as beans and onions. We could not trace those claims to studies, so they are not in this chart.
Why are so few pairings listed?
We left out anything we could not trace to a published study or an extension source. A short, honest list is more useful than a long one built on folklore.