Companion planting chart
Most companion planting charts repeat pairings that have never been tested. This one keeps them, marks them as tradition, and puts the relationships with real evidence first: pests and diseases two crops share, families that should not follow each other, and the few pairings research has looked at.
Tomatoes: companions and conflicts
Keep apart
- Corn (shared pest). Corn earworm and tomato fruitworm are the same insect, Helicoverpa zea, and corn and tomato are its most favored vegetable hosts. Source: University of Florida IFAS Extension
- Potatoes (shared disease). Late blight infects both. Its spores travel 30 to 40 miles on the wind, so distance between beds does little; Penn State's advice is to stop volunteer potatoes and tomatoes and get rid of infected tubers, which carry it over the winter. Source: Penn State Extension
- Peppers (shared disease). Bacterial spot affects both, though a different Xanthomonas species dominates on each. Avoid ground that grew either crop within the past year. Source: NC State Extension
- Black walnut (harmful to it). Tomatoes, peppers and potatoes are among the vegetables least tolerant of juglone from black walnut roots. Plant 50 to 60 feet from a mature tree. Source: Penn State Extension
Do not follow in rotation
- Peppers, Eggplant, Potatoes. Grow none of the four in the same spot more often than once every three years, and avoid ground that grew any of them the year before. Source: Clemson Cooperative Extension
Tested
- French marigold. Suppresses root-knot nematodes only as a cover crop grown for at least two months before planting; marigolds planted between crops were not effective. Source: University of Florida IFAS Extension
- Herbs. In an Iowa State trial, these crops grown with herbs had less pest trouble than without, and larger plantings of the herbs were needed for a lasting effect. Source: University of Illinois Extension
Traditional, not tested
- Basil. Said to repel thrips. Source: Utah State University Extension
Peppers: companions and conflicts
Keep apart
- Corn (shared pest). Corn is the main host of the European corn borer, whose larvae enter peppers near the stem and feed on the seed core. Corn earworm also attacks peppers. Source: University of Maryland Extension; University of Florida IFAS Extension; Clemson Cooperative Extension
- Tomatoes (shared disease). Bacterial spot affects both, though a different Xanthomonas species dominates on each. Avoid ground that grew either crop within the past year. Source: NC State Extension
- Black walnut (harmful to it). Tomatoes, peppers and potatoes are among the vegetables least tolerant of juglone from black walnut roots. Plant 50 to 60 feet from a mature tree. Source: Penn State Extension
Do not follow in rotation
- Tomatoes, Eggplant, Potatoes. Grow none of the four in the same spot more often than once every three years, and avoid ground that grew any of them the year before. Source: Clemson Cooperative Extension
Tested
- French marigold. Suppresses root-knot nematodes only as a cover crop grown for at least two months before planting; marigolds planted between crops were not effective. Source: University of Florida IFAS Extension
Traditional, not tested
- Marigold. Said to deter nematodes and other pests; research on nematodes found interplanted marigolds ineffective (see the tested entry). Source: Utah State University Extension; University of Florida IFAS Extension
Eggplant: companions and conflicts
Do not follow in rotation
- Tomatoes, Peppers, Potatoes. Grow none of the four in the same spot more often than once every three years, and avoid ground that grew any of them the year before. Source: Clemson Cooperative Extension
No tested or traditionally recommended companion in our sources.
Potatoes: companions and conflicts
Keep apart
- Tomatoes (shared disease). Late blight infects both. Its spores travel 30 to 40 miles on the wind, so distance between beds does little; Penn State's advice is to stop volunteer potatoes and tomatoes and get rid of infected tubers, which carry it over the winter. Source: Penn State Extension
- Black walnut (harmful to it). Tomatoes, peppers and potatoes are among the vegetables least tolerant of juglone from black walnut roots. Plant 50 to 60 feet from a mature tree. Source: Penn State Extension
Do not follow in rotation
- Tomatoes, Peppers, Eggplant. Grow none of the four in the same spot more often than once every three years, and avoid ground that grew any of them the year before. Source: Clemson Cooperative Extension
Traditional, not tested
- Mint or garlic. Said to deter deer with their strong scent. Source: Utah State University Extension
Cucumbers: companions and conflicts
Keep apart
- Melons and watermelon, Squash, zucchini and pumpkins (shared pest). The striped cucumber beetle spreads bacterial wilt among cucurbits. Cucumbers and cantaloupe are the most susceptible, squash and pumpkin moderately, and watermelon is almost immune. Source: University of Maryland Extension
Traditional, not tested
- Basil. Said to draw whiteflies away from young cucumbers. Source: Utah State University Extension
- Sunflowers. Used as a living support for climbing beans and cucumbers. Source: Utah State University Extension
Squash, zucchini and pumpkins: companions and conflicts
Keep apart
- Cucumbers, Melons and watermelon (shared pest). The striped cucumber beetle spreads bacterial wilt among cucurbits. Cucumbers and cantaloupe are the most susceptible, squash and pumpkin moderately, and watermelon is almost immune. Source: University of Maryland Extension
Tested
- Herbs. In an Iowa State trial, these crops grown with herbs had less pest trouble than without, and larger plantings of the herbs were needed for a lasting effect. Source: University of Illinois Extension
Traditional, not tested
- Corn, Beans. The Three Sisters: corn as a trellis for the beans, beans adding nitrogen, squash shading the soil. A traditional planting rather than a tested one. Source: Utah State University Extension; University of Illinois Extension
Melons and watermelon: companions and conflicts
Keep apart
- Cucumbers, Squash, zucchini and pumpkins (shared pest). The striped cucumber beetle spreads bacterial wilt among cucurbits. Cucumbers and cantaloupe are the most susceptible, squash and pumpkin moderately, and watermelon is almost immune. Source: University of Maryland Extension
No tested or traditionally recommended companion in our sources.
Corn: companions and conflicts
Keep apart
- Tomatoes (shared pest). Corn earworm and tomato fruitworm are the same insect, Helicoverpa zea, and corn and tomato are its most favored vegetable hosts. Source: University of Florida IFAS Extension
- Peppers (shared pest). Corn is the main host of the European corn borer, whose larvae enter peppers near the stem and feed on the seed core. Corn earworm also attacks peppers. Source: University of Maryland Extension; University of Florida IFAS Extension; Clemson Cooperative Extension
Traditional, not tested
- Beans, Squash, zucchini and pumpkins. The Three Sisters: corn as a trellis for the beans, beans adding nitrogen, squash shading the soil. A traditional planting rather than a tested one. Source: Utah State University Extension; University of Illinois Extension
Beans: companions and conflicts
Traditional, not tested
- Corn, Squash, zucchini and pumpkins. The Three Sisters: corn as a trellis for the beans, beans adding nitrogen, squash shading the soil. A traditional planting rather than a tested one. Source: Utah State University Extension; University of Illinois Extension
- Sunflowers. Used as a living support for climbing beans and cucumbers. Source: Utah State University Extension
Carrots: companions and conflicts
Traditional, not tested
- Onions and garlic. Onions are said to deter carrot flies. Source: Utah State University Extension
Onions and garlic: companions and conflicts
Traditional, not tested
- Carrots. Onions are said to deter carrot flies. Source: Utah State University Extension
Broccoli: companions and conflicts
Keep apart
- Cabbage, Kale (shared pest). The imported cabbageworm feeds on cabbage, broccoli, Brussels sprouts, cauliflower, collards, kale, turnip and radish. Source: University of Maryland Extension
Tested
- Herbs. In an Iowa State trial, these crops grown with herbs had less pest trouble than without, and larger plantings of the herbs were needed for a lasting effect. Source: University of Illinois Extension
Traditional, not tested
- Nasturtium. Grown as a trap crop to draw pests off the brassicas. Source: Utah State University Extension
Cabbage: companions and conflicts
Keep apart
- Broccoli, Kale (shared pest). The imported cabbageworm feeds on cabbage, broccoli, Brussels sprouts, cauliflower, collards, kale, turnip and radish. Source: University of Maryland Extension
Tested
- Herbs. In an Iowa State trial, these crops grown with herbs had less pest trouble than without, and larger plantings of the herbs were needed for a lasting effect. Source: University of Illinois Extension
Traditional, not tested
- Nasturtium. Grown as a trap crop to draw pests off the brassicas. Source: Utah State University Extension
Kale: companions and conflicts
Keep apart
- Broccoli, Cabbage (shared pest). The imported cabbageworm feeds on cabbage, broccoli, Brussels sprouts, cauliflower, collards, kale, turnip and radish. Source: University of Maryland Extension
Traditional, not tested
- Nasturtium. Grown as a trap crop to draw pests off the brassicas. Source: Utah State University Extension
Lettuce: companions and conflicts
Tested
- Herbs. In an Iowa State trial, these crops grown with herbs had less pest trouble than without, and larger plantings of the herbs were needed for a lasting effect. Source: University of Illinois Extension
Traditional, not tested
- Mint or garlic. Said to deter deer with their strong scent. Source: Utah State University Extension
Strawberries: companions and conflicts
Traditional, not tested
- Thyme. Said to repel worms that attack strawberries. Source: Utah State University Extension
- Borage. Grown to draw pollinators to the strawberry flowers. Source: Utah State University Extension
The guides go further for two crops: tomato companion plants, pepper companion plants.
How to read the chart
Keep apart means the two crops share a pest or a disease, or one harms the other, and a university extension source says so. Rotate means a family that can grow side by side in a season but should not follow itself on the same ground. Tested means a source cites a study. Traditional means an extension source recommends the pairing and gives a reason, but cites no study behind it.
Every entry links to the page it comes from. Where research contradicts a traditional pairing, as with marigolds planted between peppers, the entry says so.
Spacing comes first
A companion that forces a crop closer than its spacing costs more than it gives. Crowded plants hold humid air where leaf diseases start and compete for the same water. Each variety page in the catalog lists the spacing its source gives.
Sources
- Utah State University Extension, Creating sustainable school and home gardens: companion planting
- University of Illinois Extension, Companion planting: anecdotal or tried and tested?
- University of Florida IFAS Extension, Corn earworm, Helicoverpa zea
- University of Maryland Extension, European corn borer on vegetables
- Clemson Cooperative Extension, Pepper
- Penn State Extension, Tomato-potato late blight in the home garden
- NC State Extension, Bacterial spot of pepper and tomato
- University of Maryland Extension, Striped cucumber beetles and bacterial wilt
- University of Maryland Extension, Imported cabbageworm on vegetables
- Penn State Extension, Allelopathy in the home garden
- University of Florida IFAS Extension, Marigolds (Tagetes spp.) for nematode management