Companion Planting: What Research Supports and What Is Tradition
Companion planting means growing plants together for a benefit, but most popular "good neighbor" charts are tradition rather than science. Research does support a few practices: trap crops that pull pests away from a main crop, flowering plants that feed beneficial insects, and mixing crops so pests find their hosts less easily. Marigolds suppress nematodes only when grown as a dense cover crop ahead of the vegetables.
The chart
Labels: Research: supported by trials; Extension advice: recommended by a university Extension service; Tradition: common gardener practice without trial evidence.
| Plant | Good companions | Keep apart |
|---|---|---|
| Asparagus | Tomatoes (Extension advice: Classic chart pairing: tomato listed as a compatible companion for asparagus.); Calendula (Tradition: Planting calendula with asparagus rests on anecdotal pest-deterrent evidence, per UVM.) | |
| Azaleas | Hydrangeas (Extension advice: Azaleas and hydrangeas are both listed as acid-loving, making them compatible bed partners.) | |
| Basil | Asparagus (Extension advice: Listed as a traditional asparagus companion in an Extension-compiled chart; no trial cited.) | |
| Beets | Cabbages (Extension advice: Beets and cabbage-family crops listed as compatible companions.); Onions (Extension advice: Beets and the onion family listed as compatible companions.); Lettuce (Extension advice: Beets and lettuce listed as compatible companions.) | Spinach (Extension advice: Same goosefoot family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.); Swiss Chard (Extension advice: Same goosefoot family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.) |
| Blackberries | Wild brambles (Extension advice: Wild brambles nearby can spread viruses to cultivated blackberries; clear them within roughly 600 feet.) | |
| Blueberries | Azaleas (Extension advice: Both need acidic soil, so they can share an acidified bed and the same sulfur amendments.); Hydrangeas (Extension advice: OSU groups hydrangeas with blueberries as acid-soil plants that suit the same amended ground.) | |
| Broccoli | Green Beans (Extension advice: Beans listed as companions of the cabbage family, which includes broccoli.) | Cauliflower (Extension advice: Same mustard (brassica) family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.); Kale (Extension advice: Same mustard (brassica) family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.); Brussels Sprouts (Extension advice: Same mustard (brassica) family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.) |
| Brussels Sprouts | Green Beans (Research: Brussels sprouts intercropped with French beans had fewer aphids in trials.) | |
| Cabbages | Tomatoes (Research: Cabbage intercropped with tomato had less diamondback moth in trials (some traditional charts list them as incompatible).); Celery (Extension advice: Cabbage family and celery listed as compatible companions.); Onions (Extension advice: Cabbage family and onion family listed as compatible companions.); Spinach (Extension advice: Cabbage family and spinach listed as compatible companions.); Swiss Chard (Extension advice: Cabbage family and chard listed as compatible companions.); Cucumbers (Extension advice: Cucumber listed among cabbage-family companions.); Lettuce (Extension advice: Lettuce listed among cabbage-family companions.); Green Beans (Extension advice: Beans listed as companions of the cabbage family.); Chamomile (Extension advice: Chamomile near cole crops discourages imported cabbageworm egg-laying, per research Penn State summarizes.) | Broccoli (Extension advice: Same mustard (brassica) family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.); Cauliflower (Extension advice: Same mustard (brassica) family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.); Kale (Extension advice: Same mustard (brassica) family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.); Brussels Sprouts (Extension advice: Same mustard (brassica) family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.); Turnips (Extension advice: Same mustard (brassica) family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.) |
| Cantaloupes | Borage (Extension advice: Borage draws pollinators and pest predators, singled out as a good melon companion.); Chamomile (Extension advice: Chamomile flowers attract hoverflies and predatory wasps that help protect melons.) | Watermelons (Extension advice: Same gourd family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.) |
| Carrots | Onions (Research: Intercropping carrots with onions reduced carrot fly in published trials.); Tomatoes (Extension advice: Tomatoes shade heat-sensitive carrots, and carrot roots loosen soil around tomato roots.); Peas (Extension advice: Carrots and English peas listed as compatible companions.); Lettuce (Extension advice: Carrots and lettuce listed as compatible companions.); Leeks (Tradition: Traditional chart lists alliums (incl. leeks) as carrot companions; lore, not tested.); Calendula (Tradition: Calendula is suggested near carrots on anecdotal pest-repellent claims.) | Celery (Extension advice: Same carrot/parsley family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.); Dill (Extension advice: UC Master Gardener chart lists dill as incompatible with carrots; no reason given.) |
| Cauliflower | Brussels Sprouts (Extension advice: Same mustard (brassica) family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.) | |
| Celery | Tomatoes (Extension advice: Celery and tomato listed as compatible companions.); Onions (Extension advice: Celery and the onion family listed as compatible companions.) | |
| Chives | Peppers (Research: Chive odor repelled green peach aphid in lab tests and made exposed pepper plants less attractive; lab-only evidence.); Lettuce (Tradition: Chives are said to deter aphids and slugs on lettuce; Extension notes companion planting is folklore, not proven science.); Tomatoes (Extension advice: Chives are traditionally said to improve tomato health and flavor; untested claim.); Cabbages (Extension advice: Chives may distract cabbage loopers and cabbage maggots from cole crops.); Carrots (Extension advice: Chives are listed as a carrot companion that may distract carrot rust fly.) | Green Beans (Tradition: Chives are traditionally kept away from beans; folklore, not shown by trials.) |
| Cilantro | Eggplants (Extension advice: Flowering cilantro attracts predators that help control Colorado potato beetles on eggplant.); Lettuce (Extension advice: Cilantro blooms attract aphid predators such as hoverflies, helping protect lettuce and greens.); Spinach (Extension advice: Cilantro attracts beneficial insects and may distract aphids and mites near spinach.); Peas (Extension advice: Flowering cilantro supports beneficial insects and is listed as enhancing peas.); Green Beans (Extension advice: Cilantro may distract aphids and whiteflies and attracts beneficials around beans.) | |
| Collard Greens | Cabbages (Research: Collards bordering cabbage fields drew diamondback moths away; growers needed 75-100% fewer sprays with equal cabbage yield.); Tomatoes (Research: Collards interplanted with tomato had fewer flea beetles in trials.); Calendula (Extension advice: Calendula attracts predatory insects that help control aphids on collards.) | |
| Cucumbers | Sweet Corn (Research: Cucumbers interplanted with corn had fewer striped cucumber beetles in trials; corn can also trellis small vining cucumbers.); Broccoli (Research: Intercropping cucumber with broccoli reduced striped cucumber beetles in trials.); Green Beans (Extension advice: Beans as legumes can add nitrogen to soil shared with cucumbers.); Peas (Extension advice: Cucumber and English peas listed as compatible companions.); Radishes (Extension advice: Cucumber and radish listed as compatible companions.); Borage (Extension advice: Borage attracts bees and predatory insects; OSU lists cucumbers among the crops it notably helps.); Chamomile (Extension advice: Chamomile draws hoverflies and predatory wasps and is listed as a cucumber companion.) | Potatoes (Extension advice: Irish potato listed as incompatible with cucumber.); Zucchini (Extension advice: Same gourd family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.); Cantaloupes (Extension advice: Same gourd family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.); Watermelons (Extension advice: Same gourd family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.) |
| Daffodils | Tulips (Extension advice: Voles avoid toxic daffodil bulbs; interplanting them with tulips can reduce vole damage, though efficacy isn't quantified.); Daylilies (Extension advice: Emerging daylily leaves hide yellowing daffodil foliage, which must be left to ripen and feed the bulbs.) | |
| Dill | Cabbages (Extension advice: Dill nearby discourages imported cabbageworm moths from laying eggs on cabbage-family crops.); Broccoli (Extension advice: Dill masks cole crops like broccoli from cabbageworm moths and draws in parasitic wasps.); Eggplants (Extension advice: Dill flowers bring in beneficial predators that attack Colorado potato beetles on eggplant.); Lettuce (Extension advice: Dill attracts aphid-eating beneficial insects that help keep lettuce aphids in check.); Spinach (Extension advice: Dill draws hoverflies and predatory wasps that help protect leafy crops like spinach.); Onions (Extension advice: Dill attracts bees and predators and is listed as enhancing onions.); Cucumbers (Extension advice: Dill may distract squash bugs and beetles and attracts predators near cucumbers.); Cantaloupes (Extension advice: Dill brings pollinators and predatory insects to melons.) | Tomatoes (Extension advice: Lore says mature dill stunts tomatoes, though young dill is fine; not experimentally shown.) |
| Eggplants | Green Beans (Extension advice: Eggplant and beans listed as compatible companions.) | |
| Garlic | Tulips (Extension advice: Garlic is listed as a vole-deterring plant to mix among vulnerable bulbs such as tulips.) | Green Beans (Tradition: Garlic is traditionally kept away from beans; folklore, not shown by trials.); Peas (Tradition: Garlic (an allium) traditionally listed as incompatible with peas; compiled from lore.); Leeks (Extension advice: Same onion family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.) |
| Grapes | Buckwheat (Research: Cornell trials found buckwheat under mature vines cut nitrogen leaching and herbicide costs; young vines lost some vigor.); Hyssop (Extension advice: Hyssop attracts bees, butterflies and hummingbirds and is listed as enhancing grapes.) | |
| Green Beans | Pumpkins (Research: Two of the Three Sisters; beans fix nitrogen and pumpkin vines cover the ground in a polyculture that out-yields monocultures.); Winter Squash (Extension advice: Three Sisters garden: beans add nitrogen while squash vines shade out weeds.); Potatoes (Extension advice: Bush beans and Irish potatoes listed as compatible companions.); Celery (Extension advice: Bush beans and celery listed as compatible companions.); Radishes (Extension advice: Pole beans and radish listed as compatible companions.); Carrots (Extension advice: Carrot listed among bean companions.); Swiss Chard (Extension advice: Chard listed among bean companions.); Beets (Extension advice: Beets listed as companions for bush beans only; pole beans and beets are listed as incompatible elsewhere.); Peas (Extension advice: Pea listed among bean companions.); Summer savory (Extension advice: Savory is listed by OSU as enhancing beans; the benefit is a recommendation, not a tested result.) | Gladioli (Extension advice: UC Master Gardener chart lists gladiolus among plants incompatible with beans; no reason given.) |
| Green Onions | Tomatoes (Tradition: Green onions suggested for interseeding between tomato rows; Extension says this rests on experience, not research.) | |
| Kale | Green Beans (Extension advice: Beans listed as companions of the cabbage family, which includes kale.) | Collard Greens (Extension advice: Same mustard (brassica) family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.) |
| Lavenders | Cabbages (Extension advice: Lavender attracts many pollinators and is listed as enhancing cole crops.); Lettuce (Extension advice: Lavender is listed as a lettuce companion for its pollinator draw.); Tomatoes (Extension advice: Lavender near tomatoes attracts pollinators and beneficial insects.); Onions (Extension advice: OSU lists lavender as enhancing onions; mainly a pollinator attractant.) | |
| Leeks | Green Beans (Tradition: Leeks are traditionally kept away from beans; folklore, not shown by trials.) | |
| Lettuce | Tomatoes (Extension advice: Tall tomatoes shade cool-season lettuce in midsummer, slowing bolting.); Sweet Corn (Extension advice: Planting lettuce behind tall corn shields it from summer sun so it bolts later.); Cucumbers (Extension advice: Lettuce and cucumber listed as compatible companions.); Onions (Extension advice: Lettuce and the onion family listed as compatible companions.); Alyssum (Research: In a UC SAREP study of 22 plants, sweet alyssum drew aphid predators and cut lettuce aphids up to 50 feet away.); Geranium (Extension advice: OSU lists geraniums with lettuce as a possible distraction for leafhoppers.); Fennel (Extension advice: Fennel flowers attract aphid predators that help protect lettuce and greens.) | |
| Marigolds | Green Beans (Extension advice: Marigolds are said to deter Mexican bean beetles; folk claim repeated on an Extension list.); Cucumbers (Extension advice: Marigolds are believed to deter cucumber beetles; anecdotal rather than trial-backed.); Pumpkins (Extension advice: Marigolds are believed to deter squash bugs and beetles on pumpkins; anecdotal.); Tomatoes (Research: In UC Riverside field trials, French marigolds grown before tomatoes cut root-knot nematodes and raised yields like fumigation.) | |
| Mints | Cabbages (Extension advice: Mint is traditionally said to deter cabbage moths; keep it potted since it spreads aggressively.); Tomatoes (Extension advice: Traditional lists claim mint improves tomato health; contain mint to stop it spreading.) | |
| Nasturtiums | Green Beans (Extension advice: Nasturtiums are traditionally said to deter bean beetles; no supporting trial cited.); Cucumbers (Extension advice: Nasturtiums are traditionally planted with cucumbers to deter aphids and beetles.); Pumpkins (Extension advice: Nasturtiums are traditionally used around pumpkins to deter bugs and beetles.); Cantaloupes (Extension advice: Nasturtiums may distract aphids and beetles from melons and attract predatory insects.); Peas (Extension advice: Nasturtiums can distract aphids and whitefly from peas and attract predators.); Cabbages (Extension advice: Nasturtiums may draw aphids and cabbage loopers away from cole crops.) | |
| Okra | Peppers (Tradition: Traditional companion chart lists peppers with okra; compiled from gardening lore rather than trials.); Sweet Potatoes (Tradition: Traditional chart pairs okra with sweet potatoes; based on companion-planting lore.) | Green Beans (Tradition: Traditional chart lists beans as incompatible with okra; lore.) |
| Onions | Peppers (Extension advice: Pepper listed among onion companions.); Swiss Chard (Extension advice: Chard listed among onion companions.); Strawberries (Extension advice: Onions are listed as strawberry companions on traditional charts; benefit not demonstrated.) | Green Beans (Tradition: Lore says onion-family plants hinder beans; Extension notes companion planting is not proven science.); Peas (Tradition: Traditional charts list alliums as incompatible with English peas; compiled from lore.); Garlic (Extension advice: Same onion family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.); Leeks (Extension advice: Same onion family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.) |
| Oregano | Cabbages (Extension advice: Oregano flowers attract parasitic wasps that attack caterpillar pests like those on cabbage.); Cucumbers (Extension advice: Oregano is said to offer general pest protection to cucumbers; folk recommendation.); Tomatoes (Extension advice: Oregano is listed as enhancing tomatoes and distracting aphids.); Peppers (Extension advice: Oregano may distract aphids from peppers; its flowers feed beneficials.); Eggplants (Extension advice: OSU lists oregano as an eggplant companion that distracts aphids.); Potatoes (Extension advice: Oregano is listed as enhancing potatoes and distracting aphids.) | |
| Ornamental Alliums | Tulips (Extension advice: Ornamental alliums are unappealing to voles and are suggested as interplantings to help shield tulip bulbs.) | |
| Parsley | Asparagus (Extension advice: Traditional companion chart pairs parsley with asparagus; benefit not tested.); Tomatoes (Extension advice: Parsley is a classic tomato companion on traditional Extension-circulated lists; the benefit is untested.); Peppers (Extension advice: Parsley flowers attract predatory wasps that help protect peppers.); Sweet Corn (Extension advice: Parsley is listed as enhancing corn by attracting predatory wasps.); Eggplants (Extension advice: Flowering parsley attracts predatory wasps useful around eggplant.); Potatoes (Extension advice: Parsley is listed as a potato companion that attracts predatory wasps.) | |
| Peanuts | Eggplants (Tradition: Traditional chart lists eggplant as a peanut companion; lore, not tested.); Cantaloupes (Tradition: Traditional chart lists melon as a peanut companion; lore, not tested.) | Potatoes (Tradition: Traditional chart lists Irish potato as incompatible with peanuts; lore.); Onions (Tradition: Traditional chart lists alliums as incompatible with peanuts; lore.) |
| Peas | Radishes (Extension advice: English peas and radish listed as compatible companions.); Turnips (Extension advice: English peas listed as the companion for turnips.) | Potatoes (Extension advice: Irish potato listed as incompatible with English peas.); Gladioli (Extension advice: UC Master Gardener chart lists gladiolus as incompatible with English peas; no reason given.) |
| Peppers | Tarragon (Extension advice: Tarragon is listed as a good pepper companion; pest-repellent claim is not trial-backed.); Geranium (Extension advice: Geraniums are listed as enhancing peppers and possibly distracting leafhoppers and beetles.) | Cabbages (Tradition: Traditional chart lists brassicas as incompatible with peppers; lore, not tested.); Eggplants (Extension advice: Same nightshade family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.) |
| Petunias | Asparagus (Extension advice: Petunias may distract aphids, beetles and leafhoppers from asparagus.); Cucumbers (Extension advice: Petunias are listed as enhancing cucumbers by distracting aphids and beetles.); Zucchini (Extension advice: OSU lists petunias with squashes to distract aphids, beetles and leafhoppers.) | |
| Potatoes | Cabbages (Extension advice: Irish potato and cabbage family listed as compatible companions.); Buckwheat (Research: In Cornell on-farm trials, buckwheat strips beside potatoes drew predators that cut Colorado potato beetle larvae by over 95%.) | Turnips (Extension advice: Irish potato listed as incompatible with turnips.); Peppers (Extension advice: Same nightshade family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.); Eggplants (Extension advice: Same nightshade family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.) |
| Pumpkins | Cantaloupes (Extension advice: Melon listed among pumpkin companions.); Winter Squash (Extension advice: Squash listed among pumpkin companions.) | Potatoes (Extension advice: Irish potato listed as incompatible with pumpkins.); Watermelons (Extension advice: Same gourd family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.) |
| Radishes | Carrots (Extension advice: Fast radishes sprout in days and mark rows of slow-germinating carrots; pull them before they crowd the carrots.); Beets (Extension advice: Quick radishes mark rows of slower-germinating beets and are harvested early.); Lettuce (Extension advice: Radishes mark lettuce rows and are harvested before the lettuce needs the room.); Broccoli (Research: Radish intercropped with broccoli had fewer aphids in trials.); Tomatoes (Tradition: Quick radishes can be interseeded between tomato rows; based on gardener experience rather than research.) | Turnips (Extension advice: Same mustard (brassica) family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.) |
| Raspberries | Tomatoes (Extension advice: Tomatoes carry Verticillium wilt; wait four years before planting raspberries where they grew.); Potatoes (Extension advice: Potatoes leave Verticillium in soil that attacks raspberries; avoid for four years.); Peppers (Extension advice: Peppers host Verticillium wilt, so don't plant raspberries where peppers grew in the last four years.); Eggplants (Extension advice: Eggplant can leave Verticillium behind; keep raspberries off that ground for four years.); Wild brambles (Extension advice: Remove wild raspberries and blackberries within about 600 feet to limit virus spread into the planting.); Blackberries (Extension advice: Raspberries and blackberry hybrids share aphid- and pollen-spread viruses; keep plantings about 100 feet apart.) | |
| Rosemary | Green Beans (Extension advice: Rosemary's scent is claimed to deter bean beetles; traditional, unverified.); Carrots (Extension advice: Rosemary may distract carrot pests; note its large roots can compete.); Peas (Extension advice: Rosemary is listed as enhancing peas and distracting beetles.); Cabbages (Tradition: Popular lore, but a Minnesota field trial found rosemary interplanting mostly had no effect on cabbage pests.) | |
| Roses | Chives (Tradition: Lore says chives protect roses, but a Kentucky field trial found interplanted garlic chives didn't reduce Japanese beetles.) | |
| Sage | Cabbages (Extension advice: Sage's strong scent confuses imported cabbageworm adults, reducing egg-laying on cabbage.); Broccoli (Extension advice: Sage among cole crops such as broccoli discourages imported cabbageworm egg-laying.); Carrots (Extension advice: Sage may distract carrot rust fly and attracts bees near carrots.); Peas (Extension advice: Sage is listed as enhancing peas and may distract flea beetles.); Green Beans (Extension advice: Sage near beans may distract flea beetles and attracts bees.) | Cucumbers (Extension advice: Traditional lists say sage is injurious to cucumbers; no study cited.) |
| Spinach | Celery (Tradition: Traditional chart lists celery as a spinach companion; lore, not tested.); Tomatoes (Tradition: Grow spinach early, then set tomatoes into the bed as it finishes; a space-saving idea from gardener experience.) | Swiss Chard (Extension advice: Same goosefoot family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.) |
| Strawberries | Green Beans (Extension advice: Beans and strawberries appear together on traditional Extension-circulated companion lists; untested.); Borage (Extension advice: Borage flowers bring bees and predators to strawberry beds, a pairing highlighted by OSU.) | Tomatoes (Extension advice: Tomatoes host Verticillium wilt, which builds up in soil and also kills strawberries; don't plant strawberries after them.); Potatoes (Extension advice: Potatoes raise soil Verticillium levels that infect strawberries, so avoid that rotation.); Eggplants (Extension advice: Eggplant is a Verticillium host; planting strawberries where it grew risks wilt.); Peppers (Extension advice: Peppers share Verticillium wilt with strawberries, so avoid rotating strawberries after peppers.); Raspberries (Extension advice: Caneberries like raspberries are Verticillium hosts; don't plant strawberries in old cane beds.); Blackberries (Extension advice: Blackberries (caneberries) can carry Verticillium into soil later planted with strawberries.) |
| Sunflowers | Tomatoes (Extension advice: Sunflowers act as a trap crop, luring leaffooted bugs and stink bugs away from tomatoes.); Sweet Corn (Extension advice: Sunflowers are listed as enhancing corn and acting as a distraction trap for aphids and ants.) | Peas (Research: Sunflower head and root extracts significantly stunted pea root and shoot growth in tests, showing allelopathic risk; lab-scale result.) |
| Sweet Corn | Green Beans (Research: Three Sisters: corn props up climbing beans; the maize-bean-pumpkin polyculture yielded more food energy and protein per hectare than monocultures.); Pumpkins (Research: Three Sisters partners; the interplanted maize, bean and pumpkin system out-yielded monocultures in energy and protein per hectare.); Winter Squash (Extension advice: Three Sisters garden: sprawling squash smothers weeds around the corn stalks.); Zucchini (Research: Squash intercropped with corn had fewer cucumber beetles in trials summarized by SARE.); Sweet Potatoes (Research: Corn intercropped with sweet potato had fewer leaf beetles in trials.); Peanuts (Research: Corn intercropped with peanut had less corn borer in trials.); Peas (Extension advice: Corn and English peas listed as compatible companions.) | |
| Sweet Potatoes | Peppers (Tradition: Traditional chart lists peppers as a sweet potato companion; lore, not tested.) | |
| Thyme | Cabbages (Extension advice: Thyme interplanted with cole crops deters egg-laying by cabbage loopers and cabbageworms.); Broccoli (Extension advice: Thyme near broccoli and other cole crops reduces cabbage looper and cabbageworm egg-laying.) | |
| Tomatoes | Basil (Extension advice: Grow well side by side and are harvested together; Extension notes basil's pest-repelling claims still lack research.); Onions (Extension advice: Tomato and the onion family listed as compatible companions.); Cucumbers (Extension advice: Tomato and cucumber listed as compatible companions.); Peppers (Extension advice: Pepper listed among tomato companions for growing side by side; as relatives they should still not follow each other in rotation.); Borage (Extension advice: Borage is traditionally said to deter tomato hornworm; claim lacks trial support.); Tarragon (Extension advice: OSU singles out tarragon as especially good near tomatoes; claimed broad pest-repelling effect.); Calendula (Tradition: Calendula is said to repel tomato hornworms; UVM notes the evidence is only anecdotal.) | Green Beans (Tradition: Tall tomatoes can shade out sun-loving bush beans; companion advice described as unproven.); Potatoes (Extension advice: Both are attacked by the same blight, so keep them apart.); Sweet Corn (Extension advice: Corn and tomato are attacked by the same worm (corn earworm/tomato fruitworm).); Peppers (Extension advice: Same nightshade family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.); Eggplants (Extension advice: Same nightshade family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.) |
| Watermelons | Potatoes (Tradition: Traditional chart lists Irish potato as incompatible with watermelon; lore.) | |
| Winter Squash | Cucumbers (Research: Blue Hubbard squash border attracts cucumber beetles away from cucumbers; growers raised yields and cut insecticide use sharply.); Zucchini (Research: Blue Hubbard perimeter trap crop held most cucumber beetles and reduced vine borer damage in summer squash.); Cantaloupes (Research: Blue Hubbard squash perimeter trap crop protects melons by concentrating striped cucumber beetles on the border.) | |
| Zinnias | Tomatoes (Extension advice: Zinnias attract predatory insects; UVM says they may deter tomato hornworms, a hedged claim.); Cucumbers (Extension advice: Zinnias draw predators and may help deter cucumber beetles, per UVM's hedged advice.) | |
| Zucchini | Pumpkins (Extension advice: Same gourd family: don't plant one where the other grew recently; shared pests and diseases build up. Rotate 3-4 years.) |
What companion planting is
Companion planting is the practice of growing plants near each other because one helps the other: by drawing pests away, feeding beneficial insects, shading or supporting a neighbor, or making better use of space. Washington State University’s 2023 review of the science calls it a legitimate horticultural practice built on ecological principles, which researchers study under names such as intercropping, polyculture and plant associations.
The trouble is what has grown up around it. The same review finds that most companion-planting books, charts and websites lack credible supporting science, and that the idea of plants that “love” each other traces back centuries to astrology and the four elements. University of Arizona Extension puts it more bluntly: traditional companion charts have entertainment value, not scientific value. The companion lists in this site’s plant guides are labeled as tradition unless a study supports them.
What research supports
Trap crops. A trap crop draws a pest away from the main crop, where it can be destroyed. UF/IFAS lists examples: Blue Hubbard squash to lure cucumber beetles, squash bugs and squash vine borers from zucchini and cucumbers; sorghum and sunflowers to pull leaffooted bugs from tomatoes; mustard for harlequin bugs on collards; and collards to trap diamondback moth larvae away from cabbage. The details matter. UF/IFAS plants trap crops before the main crop, sometimes 3-4 weeks ahead, at least 5 feet away, at roughly 10-20% of the main crop’s area, and removes the pests that gather. Iowa State cautions that Blue Hubbard needs more space than most home gardens have, and UF/IFAS notes only limited cases of trap cropping working well for growers.
Flowers for beneficial insects. Many predators and parasitoids eat nectar or pollen as adults. Hover fly adults feed on flowers while their larvae eat aphids, and tiny, stingless parasitic wasps lay eggs in caterpillars such as hornworms (UF/IFAS Orange County). Research-backed insectary plants include sweet alyssum, buckwheat, fennel, sunflower and mustard (University of Missouri IPM), and dill, parsley and cilantro in bloom (UF/IFAS). Results are real but modest: in an Oregon State broccoli trial, sweet alyssum drew the most hover flies and nearly doubled parasitism of cabbage aphids, yet aphid numbers were not significantly lower. Oregon State calls insectary plantings “not a silver bullet”. Keep something in bloom all season.
Mixing crops. UF/IFAS notes that pests that feed on a narrow range of plants, such as diamondback moth on cabbage-family crops, are more readily reduced when host crops are mixed with non-hosts. WSU explains that many insects find host plants by landing on green surfaces, so non-host leaves interrupt the search. It also suggests pairing deep-rooted crops such as carrots and radishes with shallow-rooted ones such as lettuce and onions to reduce competition for water.
What is mostly tradition
- Repellent herbs. Field research has not shown that mint or other aromatic plants repel pests in the open garden (WSU).
- Marigolds as companions. Interplanted marigolds do not reliably control nematodes (UF/IFAS) and can deter beneficial insects (WSU). Mississippi State reports a few studies with benefits, such as basil and marigolds reducing thrips on tomatoes, which shows results depend on the crop and pest.
- “Good” and “bad” neighbor lists. Most pairings in popular charts have never been tested.
Two special cases
Marigolds for nematodes. Marigold roots release a compound that suppresses root-knot and lesion nematodes. UF/IFAS recommends French marigolds grown densely, less than 7 inches apart, for at least two months, then turned into the soil before planting vegetables, and repeating each season.
Black walnut. Wisconsin Extension lists tomatoes, potatoes, peppers and eggplant as sensitive to juglone from walnut trees, based on observation. WSU and Maryland Extension point out there is no conclusive evidence that juglone causes the poor growth seen near walnuts; shade and root competition may explain it.
Questions
Is companion planting scientifically proven?
Some parts are and most are not. A 2023 Washington State University review calls companion planting a legitimate practice based on ecology but says most companion books, charts and websites lack credible science. Trap cropping, insectary plants and intercropping have research behind them; claims that particular plants "love" or "hate" each other generally do not.
Do marigolds keep pests away from vegetables?
Not as interplanted companions. UF/IFAS says marigolds reduce root-knot and some other nematodes only when grown as a dense cover crop for at least two months and then turned in before the vegetables are planted; interplanting them with crops does not appear to work. WSU adds that marigolds can deter beneficial insects as well as pests.
Does planting basil or mint near vegetables repel insects?
There is little field evidence. WSU's review notes that aromatic compounds can repel insects in the lab, but in the open garden they dissipate quickly and field research has not shown a repellent effect for mint or other aromatic herbs.
Do the Three Sisters (corn, beans and squash) grow better together?
The Three Sisters is a traditional Native American planting in which corn supports the beans and squash shades the soil. WSU found few field studies and no compelling published evidence that it improves yields or soil, although there are good cultural and historical reasons to grow it.
Sources
- Gardening with Companion Plants (EM128E) · Washington State University Extension
- Companion Planting · University of Arizona Cooperative Extension
- Companion planting: myth or truth? · Mississippi State University Extension
- Intercropping, Crop Diversity and Pest Management (IN922) · UF/IFAS Extension
- Trap Cropping · UF/IFAS Gardening Solutions
- Trap Crops Help Combat Pests in the Garden · UF/IFAS Extension Leon County
- How do I prevent damage to my squash plants from squash vine borer? · Iowa State University Extension and Outreach
- Alyssum attracts predator insects into broccoli fields · Oregon State University
- Increasing beneficial insects using insectary plants · University of Missouri Integrated Pest Management
- Using insectary plants to attract pest predators · UF/IFAS Extension Orange County
- Marigolds (Tagetes spp.) for Nematode Management (NG045) · UF/IFAS Extension
- Cover Crops for Managing Root-Knot Nematodes (IN892) · UF/IFAS Extension
- Three Sisters Gardening Method · West Virginia University Extension
- Black Walnut Toxicity · University of Wisconsin-Madison Extension
- Do Black Walnut Trees Have Allelopathic Effects on Other Plants? · Washington State University Extension
- Walnut Toxicity (Juglone) · University of Maryland Extension
- Food Yields and Nutrient Analyses of the Three Sisters: A Haudenosaunee Cropping System · Ethnobiology Letters 7(1):87-98 (Mt.Pleasant, 2016)
- Companion Plants for the Vegetable Garden (column by Vijai Pandian) · University of Wisconsin-Madison Division of Extension, Kenosha County
- Table 6: Intercropping for Pest Reduction - Successful Scientific Trials (Manage Insects on Your Farm) · SARE Outreach (USDA Sustainable Agriculture Research and Education)
- Companion Planting · Oregon State University Extension Service
- Companion Planting (Food Hero tip sheet) · Washington State University SNAP-Ed / Food Hero (Oregon State University Extension)
- Companion Planting Chart: Companion Planting for Edible Crops · University of California Agriculture and Natural Resources (UCCE Master Gardener Program)
- Growing Radishes in a Home Garden · University of Maryland Extension
- A Salad That Diamondback Moths Can't Resist · USDA Agricultural Research Service
- Surrounding Crops With Perimeter Fools Pests (Manage Insects on Your Farm) · SARE Outreach (USDA Sustainable Agriculture Research and Education)
- Perimeter Trap Cropping: A Novel Approach to Insect Pest Control · University of Vermont Extension
- Olfactory response of Myzus persicae (Homoptera: Aphididae) to volatiles from leek and chive: Potential for intercropping with sweet pepper · Acta Agriculturae Scandinavica Section B, Soil and Plant Science (2007), via Swedish University of Agricultural Sciences
- Companion Planting & Botanical Pesticides: Concepts & Resources · ATTRA, National Center for Appropriate Technology (NCAT)
- The Art of Companion Planting · University of Arizona Cooperative Extension, Yavapai County Master Gardeners
- Interseeding in the Home Garden · Ohio State University Extension (Fairfield County Master Gardeners)
- Rotate Your Vegetables! · N.C. Cooperative Extension, Wayne County Center
- Herbs Make Good Plant Partners and Companions · Penn State Extension
- Marigolds for Nematode Control · Department of Nematology, University of California, Riverside (Ploeg lab)
- Aphid Relief from Sweet Alyssum · University of California, Davis (report on UC SAREP-funded research)
- Strawberry (Fragaria spp.)-Verticillium Wilt · Pacific Northwest Plant Disease Management Handbook (Oregon State University, Washington State University, University of Idaho Extension)
- Bulletin #2066, Growing Raspberries and Blackberries · University of Maine Cooperative Extension
- Protect Your Garden: Organic Vole Control for Fall and Winter · N.C. Cooperative Extension, Beaufort County Center
- Separation needed for rasp- and boysen-berries? · Ask Extension (answered by Oregon State University Extension)
- Allelopathic effect of aqueous extracts of common sunflower on seed germination and growth of field pea · Zemdirbyste-Agriculture, Vol. 110, No. 1 (2023) - D. Janusauskaite
- Herbs and Flowers in the Vegetable Garden · Oregon State University Extension Service
- Effect of a Hay Mulch and of a Companionate Planting on Cabbage Pest Populations · The Great Lakes Entomologist 17(1), 1984 - W. S. Cranshaw
- Investigating the Use of Buckwheat Strips To Attract Beneficial Insects for the Management of Colorado Potato Beetles (Final Report, Organic Farming Research Foundation) · Cornell Cooperative Extension, Cornell Vegetable Program (R. Hadad)
- How to acidify soil for rhododendrons, azaleas and other acid-loving plants · Oregon State University Extension Service
- Creating a Biodiverse Vegetable Garden · University of Vermont Extension
- Evaluating Companion Planting and Non-host Masking Odors for Protecting Roses from the Japanese Beetle (Coleoptera: Scarabaeidae) · Journal of Economic Entomology 96(1):81-87, 2003 - Held, Gonsiska & Potter (University of Kentucky)
- Study: Vineyard cover crops save expense, environment · Cornell University College of Agriculture and Life Sciences
- Don't Touch the Daffodils! · Mississippi State University Extension Service