What Is Companion Planting?
Companion planting is growing different plants close together so one helps the other — by trapping or confusing pests, feeding pollinators and predatory insects, adding support or shade, or sharing space efficiently. It also means separating plants that share diseases or compete.
Researchers call the practice intercropping or polyculture and measure it in yield per acre, pest counts and disease levels. Garden companion lists grew up separately, in 20th-century gardening books and seed catalogs, and many of their pairings were never tested. A useful chart keeps both: the documented effects, the practical rules of thumb, and the traditions labeled as traditions.
A good companion relationship usually has a mechanism you can name. Dill helps cabbage because its flowers feed the parasitic wasps that kill cabbage worms; lettuce does well beside tomatoes because the tomato canopy shades it in July. When a pairing has no plausible mechanism — such as the claim that tomatoes “love” carrots — treat it as folklore.
How Does Companion Planting Work?
Companion planting works through six main mechanisms: trap cropping, habitat for beneficial insects, scent masking, nitrogen fixing, physical support or shade, and allelopathy, where chemicals from one plant suppress another. Each works only under specific conditions of density, timing and distance.
| Mechanism | How it works | Garden example |
|---|---|---|
| Trap cropping | A plant pests prefer draws them away from the main crop; the trap plants are then removed or sprayed. | Blue Hubbard squash around zucchini and cucumbers draws cucumber beetles and squash vine borers. |
| Beneficial insect habitat | Small, open flowers feed hoverflies, lacewings and parasitic wasps, whose larvae eat aphids and caterpillars. | Sweet alyssum in lettuce; dill and cilantro flowers near cabbage. |
| Scent masking and pest confusion | Strong-smelling plants may make it harder for pests to find a host by scent or sight. | Onions between carrot rows against carrot rust fly — effective only at high onion density. |
| Nitrogen fixing | Bean and pea roots host bacteria that turn air nitrogen into plant food, released as roots and leaves decay. | Beans before cabbage or corn; the main gain goes to the following crop. |
| Physical support and shade | Tall or sturdy plants hold up climbers or shade heat-sensitive crops. | Pole beans on corn; lettuce in the shade of tomatoes or a cucumber trellis. |
| Allelopathy | Some plants release chemicals from roots, leaves or residue that suppress germination or growth of others. | Black walnut juglone kills tomatoes; sunflower residue suppresses some weeds. |
The six mechanisms behind companion planting, with examples from the chart above.
Nitrogen fixing is the most misunderstood mechanism. Beans and peas host rhizobium bacteria in root nodules, but the plants keep most of that nitrogen for themselves, and a large share leaves the garden with the harvested pods. Neighboring corn or squash gains little the same season; the crop planted after the legumes gains more once roots and leaves decay. Cutting pea and bean vines at the soil line and leaving the roots in the ground maximizes the benefit.
Beneficial insects have the strongest research record. Hoverflies, lacewings and parasitic wasps need nectar and pollen as adults, and small, open flowers such as sweet alyssum, dill, cilantro and buckwheat let them live and breed near the crop. Their larvae then eat aphids, caterpillars and thrips.
What Is the Three Sisters Planting Method?
The Three Sisters is an Indigenous North American planting of corn, pole beans and squash in one mound. Corn gives the beans a pole to climb, squash leaves shade the soil against weeds and drought, and intercropping studies often find more total harvest per acre than separate plots.
Timing makes the method work. Plant corn first and wait until it is about 6 inches (15 cm) tall — typically two to three weeks — before sowing pole beans at its base, so the beans don't pull young corn over. Squash or pumpkins go around the outside of the mound at the same time as the beans or a week later. Mounds are commonly about 4 feet (1.2 m) across and a similar distance apart, with several corn plants in each.
Beans in the Three Sisters are usually credited with feeding the corn. The bean nitrogen benefit to corn in the same season is small; the soil builds up nitrogen over years of residue returned to it. Choose vigorous pole beans and a sturdy field or flour corn, since thin sweet corn stalks can buckle under heavy bean vines.
Does Companion Planting Actually Work?
Some companion planting clearly works and much of it is untested. Of the 243 pairs in this chart, 62 are research-supported, 55 rest on practical horticulture and 126 are traditional claims. Flowers that feed beneficial insects and separating disease-sharing crops have the best evidence.
The table checks well-known companion planting claims against what research and plant pathology show. “Traditional” doesn't mean false — it means untested or inconsistent, so it's fine to follow a tradition that costs nothing, as long as you don't rely on it for pest control.
| Popular claim | What the evidence shows | Evidence |
|---|---|---|
| Tomatoes and potatoes shouldn't grow together | Both host late blight, early blight, Verticillium wilt and Colorado potato beetles, so one crop feeds disease to the other. | Research-supported |
| Sweet alyssum controls aphids | Its flowers feed hoverflies whose larvae eat aphids; organic lettuce growers in California interplant it for this purpose. | Research-supported |
| Marigolds repel garden pests | French marigold roots suppress root-knot and lesion nematodes when grown densely for a season. As a border they do little against insects. | Research-supported |
| Beans feed nitrogen to their neighbors | Fixed nitrogen mostly stays in the bean plant until its roots and leaves decay, so the next crop benefits more than this season's neighbors. | Research-supported |
| Onions protect carrots from carrot fly | Trials show a benefit only when onions heavily outnumber carrots and are actively growing; one onion row does little. | Traditional |
| Basil makes tomatoes taste better | There's no controlled evidence. Basil pairs well with tomatoes because both need the same heat, sun and water. | Traditional |
| Fennel harms everything near it | Fennel extracts inhibit germination in lab tests, but field evidence is thin. The documented problem is that fennel crosses with dill. | Traditional |
Common companion planting claims and how well they hold up.
What Plants Should Not Be Planted Together?
Keep apart plants that share pests and diseases — tomatoes and potatoes (late blight), tomatoes and sweet corn (corn earworm), strawberries and any nightshade (Verticillium wilt). Keep tomatoes clear of black walnut roots, and separate dill from fennel, which cross-pollinate.
The research-supported conflicts below come from shared pathogens, shared insect pests and documented allelopathy. Traditional conflicts, such as keeping beans away from onions and garlic, appear in the full chart and the crop lookup with their own label.
| Keep apart | Why |
|---|---|
| Tomatoes ✕ Potatoes | Both are nightshades that share late blight, early blight, Verticillium wilt and Colorado potato beetles; spores and pests move from one crop to the other. |
| Tomatoes ✕ Corn | The corn earworm and the tomato fruitworm are the same insect (Helicoverpa zea); a corn patch next to tomatoes can raise fruitworm numbers. |
| Tomatoes ✕ Black Walnut | Tomatoes are among the most juglone-sensitive plants: black walnut roots release juglone, and tomatoes wilt and die within the tree's root zone. |
| Peppers ✕ Potatoes | Potatoes share Verticillium wilt and potato virus Y with peppers; aphids spread the virus from potato plants to nearby peppers. |
| Peppers ✕ Corn | European corn borers and corn earworms both feed in pepper fruit; a nearby corn patch can raise their numbers. |
| Eggplant ✕ Potatoes | Colorado potato beetles build up on potatoes and move to eggplant, their other favorite host; both crops also share Verticillium wilt. |
| Strawberries ✕ Potatoes | Potatoes host Verticillium wilt, a soil fungus that survives for years and kills strawberry plants. Don't grow strawberries near or after potatoes. |
| Strawberries ✕ Tomatoes | Tomatoes host Verticillium wilt, a soil fungus that survives for years and kills strawberry plants. Don't grow strawberries near or after tomatoes. |
| Strawberries ✕ Peppers | Peppers host Verticillium wilt, a soil fungus that survives for years and kills strawberry plants. Don't grow strawberries near or after peppers. |
| Strawberries ✕ Eggplant | Eggplant hosts Verticillium wilt, a soil fungus that survives for years and kills strawberry plants. Don't grow strawberries near or after eggplant. |
| Spinach ✕ Beets | Spinach and beets are close relatives that share the spinach leafminer, whose larvae tunnel through both crops' leaves. |
| Carrots ✕ Celery | Carrots and celery share the carrot rust fly; planting them side by side gives the fly an easy path between crops. |
| Carrots ✕ Parsley | Parsley is a host of the carrot rust fly, so a parsley patch next to carrots can keep the pest close; cover both with netting or grow them apart. |
| Dill ✕ Fennel | Dill and fennel can cross-pollinate, producing off-flavored hybrid seedlings; plant them far apart if you save seed or let them self-sow. |
Plant pairs to keep apart with research-supported reasons.
What Grows Well Together? Full Companion Planting Chart
The companion planting chart below lists the good companions and plants to avoid for all 46 crops. Each crop name opens a guide with the reason and evidence level behind every pairing, plus a planting layout for that crop.
| Crop | Good companions | Keep away from |
|---|---|---|
| Tomatoes | Marigolds, Parsley, Dill, Sweet Alyssum, Lettuce, Spinach, Basil, Borage, Carrots, Chives, Garlic, Nasturtiums, Asparagus, Mint | Potatoes, Corn, Black Walnut, Strawberries, Fennel, Cabbage, Broccoli, Cauliflower, Kale |
| Peppers | Marigolds, Sweet Alyssum, Cilantro, Spinach, Lettuce, Basil, Onions, Carrots, Oregano, Nasturtiums, Chives | Potatoes, Corn, Strawberries, Fennel, Black Walnut |
| Eggplant | Marigolds, Sweet Alyssum, Spinach, Lettuce, Beans, Basil, Thyme | Potatoes, Strawberries, Fennel, Black Walnut |
| Potatoes | Sweet Alyssum, Beans, Corn, Marigolds, Cabbage | Tomatoes, Peppers, Eggplant, Strawberries, Pumpkins, Zucchini, Melons, Watermelon, Asparagus, Cucumbers, Sunflowers, Black Walnut |
| Sweet Potatoes | Marigolds, Radishes, Beans, Thyme | Pumpkins, Watermelon |
| Cucumbers | Dill, Borage, Pumpkins, Peas, Lettuce, Nasturtiums, Marigolds, Radishes, Beans, Corn, Sunflowers | Potatoes, Sage, Fennel |
| Zucchini | Borage, Dill, Pumpkins, Nasturtiums, Marigolds, Beans, Corn, Radishes, Oregano | Potatoes, Fennel |
| Pumpkins | Cucumbers, Zucchini, Corn, Beans, Borage, Sunflowers, Nasturtiums, Marigolds, Radishes | Potatoes, Sweet Potatoes |
| Melons | Marigolds, Borage, Sweet Alyssum, Lettuce, Nasturtiums, Radishes | Potatoes |
| Watermelon | Marigolds, Borage, Sweet Alyssum, Nasturtiums, Radishes, Sunflowers | Potatoes, Sweet Potatoes |
| Strawberries | Borage, Chives, Sweet Alyssum, Marigolds, Spinach, Lettuce, Onions, Garlic, Thyme, Beans, Blueberries | Potatoes, Tomatoes, Peppers, Eggplant, Mint, Cabbage |
| Blueberries | Borage, Sweet Alyssum, Strawberries | Lavender, Rosemary, Thyme, Black Walnut |
| Lettuce | Sweet Alyssum, Cilantro, Dill, Tomatoes, Peppers, Eggplant, Cucumbers, Melons, Radishes, Carrots, Onions, Beets, Sunflowers, Broccoli, Cauliflower, Leeks, Strawberries, Chives | Fennel |
| Spinach | Tomatoes, Peppers, Eggplant, Peas, Broccoli, Cauliflower, Cilantro, Strawberries, Radishes | Beets |
| Kale | Dill, Sweet Alyssum, Cilantro, Beets, Nasturtiums, Onions, Thyme, Celery, Radishes, Mint | Tomatoes |
| Cabbage | Dill, Sweet Alyssum, Cilantro, Beets, Potatoes, Nasturtiums, Onions, Thyme, Sage, Rosemary, Mint, Celery, Garlic, Leeks | Tomatoes, Strawberries |
| Broccoli | Dill, Sweet Alyssum, Cilantro, Spinach, Lettuce, Beets, Nasturtiums, Onions, Rosemary, Thyme, Celery, Radishes, Mint | Tomatoes |
| Cauliflower | Dill, Sweet Alyssum, Spinach, Lettuce, Nasturtiums, Celery, Onions, Thyme, Beans | Tomatoes |
| Carrots | Lettuce, Radishes, Tomatoes, Peppers, Onions, Leeks, Chives, Peas, Rosemary, Sage | Celery, Parsley, Dill, Fennel |
| Beets | Lettuce, Kale, Cabbage, Broccoli, Onions, Garlic | Spinach, Beans |
| Radishes | Sweet Potatoes, Lettuce, Carrots, Peas, Cucumbers, Zucchini, Pumpkins, Melons, Watermelon, Spinach, Kale, Broccoli | — |
| Onions | Lettuce, Beets, Peppers, Strawberries, Kale, Cabbage, Broccoli, Cauliflower, Carrots | Beans, Peas, Asparagus |
| Garlic | Tomatoes, Strawberries, Cabbage, Beets | Beans, Peas, Asparagus |
| Leeks | Lettuce, Carrots, Celery, Cabbage | Beans, Peas |
| Beans | Pumpkins, Corn, Eggplant, Potatoes, Sweet Potatoes, Cucumbers, Zucchini, Strawberries, Cauliflower, Marigolds | Beets, Onions, Garlic, Leeks, Chives, Fennel, Sunflowers |
| Peas | Cucumbers, Spinach, Radishes, Carrots | Onions, Garlic, Leeks, Chives |
| Corn | Pumpkins, Beans, Potatoes, Cucumbers, Zucchini, Sunflowers | Tomatoes, Peppers |
| Asparagus | Tomatoes, Parsley, Basil, Marigolds | Potatoes, Onions, Garlic |
| Celery | Kale, Cabbage, Broccoli, Cauliflower, Leeks | Carrots |
| Basil | Parsley, Chives, Tomatoes, Peppers, Eggplant, Asparagus | Rosemary, Sage |
| Dill | Tomatoes, Cucumbers, Zucchini, Kale, Cabbage, Broccoli, Cauliflower, Lettuce | Fennel, Carrots |
| Cilantro | Peppers, Lettuce, Kale, Cabbage, Broccoli, Spinach | Fennel |
| Parsley | Tomatoes, Basil, Chives, Asparagus | Carrots, Mint |
| Mint | Kale, Cabbage, Broccoli, Tomatoes | Strawberries, Parsley |
| Rosemary | Sage, Thyme, Lavender, Oregano, Cabbage, Broccoli, Carrots | Blueberries, Basil |
| Thyme | Rosemary, Sage, Lavender, Oregano, Eggplant, Sweet Potatoes, Strawberries, Kale, Cabbage, Broccoli, Cauliflower | Blueberries |
| Oregano | Rosemary, Thyme, Sage, Lavender, Peppers, Zucchini | — |
| Chives | Strawberries, Basil, Parsley, Tomatoes, Peppers, Lettuce, Carrots | Beans, Peas |
| Sage | Rosemary, Thyme, Oregano, Lavender, Cabbage, Carrots | Basil, Cucumbers |
| Fennel | — | Dill, Tomatoes, Peppers, Eggplant, Cucumbers, Zucchini, Lettuce, Carrots, Beans, Cilantro |
| Marigolds | Tomatoes, Peppers, Eggplant, Sweet Potatoes, Melons, Watermelon, Strawberries, Potatoes, Cucumbers, Zucchini, Pumpkins, Beans, Asparagus | — |
| Nasturtiums | Tomatoes, Peppers, Cucumbers, Zucchini, Pumpkins, Melons, Watermelon, Kale, Cabbage, Broccoli, Cauliflower | — |
| Sunflowers | Pumpkins, Lettuce, Cucumbers, Watermelon, Corn | Potatoes, Beans |
| Borage | Cucumbers, Zucchini, Pumpkins, Melons, Watermelon, Strawberries, Blueberries, Tomatoes | — |
| Lavender | Rosemary, Thyme, Oregano, Sage | Blueberries |
| Sweet Alyssum | Tomatoes, Peppers, Eggplant, Potatoes, Melons, Watermelon, Strawberries, Blueberries, Lettuce, Kale, Cabbage, Broccoli, Cauliflower | — |
Vegetable, herb, fruit and flower companion planting chart. Plants not listed for a crop have no known effect on it.
How Do You Plan a Companion Planting Garden?
Plan a companion garden in four steps: list the crops you want, check every pair for conflicts, group crops by plant family for rotation, then place tall crops on the north side with low companions and flowers in the gaps and at bed ends.
Enter your crop list in the garden checker above to see every pair at once; conflicts such as tomatoes and potatoes mean separate beds, ideally not next to each other. Crops in the same family — nightshades, brassicas, cucurbits, alliums — share soil pests, so they rotate as a group to a new bed each year.
Companions still need room: work out how many plants fit in each bed with the plant spacing calculator for square foot and row gardens. Timing matters as much as spacing, because cool-season companions such as spinach and radishes fill beds before warm-season crops can go out after your last spring frost date. New beds for a companion layout can be sized with the raised bed soil calculator, one of several free garden planning tools on PlantoScan.
Put nectar flowers — sweet alyssum, dill, cilantro, borage — at the end of every bed and let a few herbs bolt. That single step has more evidence behind it than any one-to-one pairing in the chart.
Frequently Asked Questions
- What is the best companion plant for tomatoes?
- French marigolds and flowering herbs such as dill, parsley and sweet alyssum are the best-supported tomato companions: marigolds grown densely before tomatoes suppress root-knot nematodes, and the flowers feed insects that eat tomato pests. Basil is the classic partner because it shares tomatoes' sun and watering needs.
- What should you not plant with tomatoes?
- Don't plant tomatoes next to potatoes, which share late blight, early blight and Verticillium wilt, or next to sweet corn, whose corn earworm is the same insect as the tomato fruitworm. Keep tomatoes outside the root zone of black walnut trees, and give fennel and cabbage-family crops their own beds.
- What are the best companion plants for cucumbers?
- Borage and flowering dill are the best cucumber companions because cucumbers need bees and the flowers feed aphid predators. Peas share the cucumber trellis in spring, lettuce grows in its shade, and a border of Blue Hubbard squash traps cucumber beetles. Keep cucumbers away from potatoes and sage.
- What can you plant with peppers?
- Peppers grow well with basil, onions, oregano, carrots and spinach, and with sweet alyssum or flowering cilantro that feed aphid-eating hoverflies. Keep peppers away from potatoes, which spread Verticillium wilt and potato virus Y, and from sweet corn, which harbors corn borers and earworms.
- What flowers are best for companion planting?
- Sweet alyssum, French marigolds, borage, nasturtiums and sunflowers are the most useful companion flowers. Alyssum feeds aphid-eating hoverflies, marigolds suppress root-knot nematodes, borage and sunflowers draw pollinators, and nasturtiums work as a trap crop for aphids and cabbage whites.
- Is a companion planting chart scientifically accurate?
- Most companion planting charts mix research with folklore without saying which is which. In PlantoScan's chart, 62 of 243 plant pairs are research-supported, 55 rest on practical horticulture and 126 are traditional claims, and every pair is labeled so you can judge for yourself.
Companion data: PlantoScan's own editorial compilation, written from general horticultural knowledge, plant pathology and published intercropping research. Evidence labels are our editorial judgment of how well each claim is supported; no third-party chart was copied. Results vary with climate, soil, variety and pest pressure.