Companion Planting Chart
Good and bad neighbors for 28 vegetables, herbs and flowers, with the evidence behind each pair. Look up any plant, check two plants together and lay out a bed that keeps the poor pairs apart.
1.Finding a plant’s companions
Choose a plant to list its good neighbors and the ones to keep apart, each with the reason and how strong the evidence is. Most pairings come from traditional extension charts; a few were tested in field trials, and a few rest on a documented disease or pest link.
TomatoTomato family. Sun-hungry; shares blight and wilt with potato and pepper.Good neighbors (12)
Basilfield-testedBasil grown with tomatoes cut thrips in field and greenhouse trials.
Marigoldfield-testedMarigolds cut thrips on tomatoes in trials; nematode control needs a dense marigold crop first.
Asparagustradition onlyTomatoes set beside the asparagus row after its harvest.
Boragetradition onlySaid to deter tomato hornworm; untested.
Carrottradition onlyA classic of traditional charts; no trials found.
Cucumbertradition onlyListed as compatible on traditional charts.
Garlictradition onlySaid to protect tomatoes from spider mites; untested.
Lettucetradition onlyHead lettuce listed as a good neighbor.
Nasturtiumtradition onlyListed as compatible on traditional charts.
Oniontradition onlyListed as compatible on traditional charts.
Parsleytradition onlyListed as compatible on traditional charts.
Thymetradition onlyListed as a helper on traditional charts.
Keep apart (5)
Cornsound practiceCorn earworm is the tomato fruitworm; moths move to tomatoes when corn silks turn brown.
Potatosound practiceBoth host late blight; infected potato tubers are a main early source of the disease.
Strawberrysound practiceVerticillium wilt: no strawberries where tomatoes grew in the past 5 years.
Cabbage familytradition onlyKept apart on traditional charts; no trials found.
Fenneltradition onlyFennel is said to stunt most neighbors; little evidence.
Sources disagree (1)
Dilltradition onlyYoung dill is listed as a help, mature dill as a harm.
Check two plants
2.The whole matrix
All 28 plants against each other. Find a plant in the left column and read across; select a coloured cell to see the reason and its sources. Blank cells mean no source lists the pair, which usually means it is fine.
| Plant | Tomato | Pepper  | Potato | Bean  | Pea  | Corn | Squash  | Cucumber | Cabbage family | Radish  | Lettuce | Carrot | Beet  | Spinach  | Onion | Garlic | Strawberry | Asparagus | Basil | Thyme | Dill | Fennel | Parsley | Borage | Marigold | Nasturtium | Sunflower  | Sweet alyssum  |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Tomato | ||||||||||||||||||||||||||||
| Pepper | ||||||||||||||||||||||||||||
| Potato | ||||||||||||||||||||||||||||
| Bean | ||||||||||||||||||||||||||||
| Pea | ||||||||||||||||||||||||||||
| Corn | ||||||||||||||||||||||||||||
| Squash | ||||||||||||||||||||||||||||
| Cucumber | ||||||||||||||||||||||||||||
| Cabbage family | ||||||||||||||||||||||||||||
| Radish | ||||||||||||||||||||||||||||
| Lettuce | ||||||||||||||||||||||||||||
| Carrot | ||||||||||||||||||||||||||||
| Beet | ||||||||||||||||||||||||||||
| Spinach | ||||||||||||||||||||||||||||
| Onion | ||||||||||||||||||||||||||||
| Garlic | ||||||||||||||||||||||||||||
| Strawberry | ||||||||||||||||||||||||||||
| Asparagus | ||||||||||||||||||||||||||||
| Basil | ||||||||||||||||||||||||||||
| Thyme | ||||||||||||||||||||||||||||
| Dill | ||||||||||||||||||||||||||||
| Fennel | ||||||||||||||||||||||||||||
| Parsley | ||||||||||||||||||||||||||||
| Borage | ||||||||||||||||||||||||||||
| Marigold | ||||||||||||||||||||||||||||
| Nasturtium | ||||||||||||||||||||||||||||
| Sunflower | ||||||||||||||||||||||||||||
| Sweet alyssum |
Figure 2. The companion matrix: 28 plants and the pairs listed by Cornell, UF/IFAS and West Virginia University Extension, marked where trials or a documented link back them up.
3.Planning a bed
Lay out a 4 by 8 ft bed in 1 ft squares. Choose a plant, then tap squares to place it. Neighbors that share an edge are checked against the chart: clashes are outlined and listed, good pairs are counted. The sample bed is the one on the poster.
Placing: Tomato
32 of 32 squares planted. Edge neighbors only; diagonal squares are not compared.
Clashes (0)
- No keep-apart pairs share an edge.
Good pairs (17)
- Tomato and basil field-testedBasil grown with tomatoes cut thrips in field and greenhouse trials.
- Tomato and marigold field-testedMarigolds cut thrips on tomatoes in trials; nematode control needs a dense marigold crop first.
- Tomato and carrot tradition onlyA classic of traditional charts; no trials found.
- Basil and pepper tradition onlySimilar needs for sun, warmth and water.
- Onion and carrot field-testedOnions cut carrot fly attack, most while the onions were young and outnumbered the carrots.
- Carrot and lettuce tradition onlyListed as compatible on traditional charts.
- Onion and beet tradition onlyListed as compatible on traditional charts.
- Carrot and cabbage family tradition onlyListed as compatible on traditional charts.
- Lettuce and radish tradition onlyListed as especially good on traditional charts.
- Lettuce and sweet alyssum field-testedAlyssum feeds hover flies whose larvae eat aphids; effect seen up to 50 ft away.
- Lettuce and beet tradition onlyListed as compatible on traditional charts.
- Beet and cabbage family tradition onlyListed as compatible on traditional charts.
- Cabbage family and thyme field-testedThyme cut cabbage looper and imported cabbageworm damage in an Iowa broccoli study.
- Cabbage family and radish sound practiceRadish works as a sacrificial trap crop for flea beetles and root maggots.
- Cabbage family and nasturtium field-testedNasturtium cut cabbageworm damage in Iowa studies.
- Spinach and radish tradition onlyListed as compatible on traditional charts.
- Radish and nasturtium tradition onlyListed as a helper on traditional charts.
4.Why pairs work
Where companion planting works, it works through a handful of well-understood effects. Where it fails, a shared disease, a shared pest or plain competition is usually the cause.
Trap crops
A plant the pest prefers, set at the edge and removed once infested. A Blue Hubbard squash border cut cucumber beetle and squash vine borer infestations on summer squash by up to 95% and 88%.
Hiding the host
Mixed plantings make it harder for specialist pests to land on their crop. In trials, any green non-host leaves worked about as well as strong-smelling herbs.
Feeding the predators
Small open flowers such as sweet alyssum, dill, fennel and parsley in bloom feed hover flies, lacewings and parasitic wasps that eat pests.
Nitrogen from legumes
Beans and peas host nitrogen-fixing bacteria in root nodules and add nitrogen to the soil around them.
Support and shade
Corn holds up pole beans; broad squash leaves shade the soil, holding moisture and smothering weeds.
Why some pairs fail
Shared diseases and pests, competition for light and water, and plant chemicals such as juglone from black walnut, which harms the tomato family.
5.The Three Sisters
Corn, pole beans and squash grown in one mound is the best-studied companion planting of all. In Haudenosaunee plots in New York, the three together gave more food per hectare than the same crops grown apart.
- Build mounds. Raised mounds a few feet wide, room for 7–10 corn plants in the middle.
- Sow the corn. Thin to one plant every 8 inches once it sprouts.
- Add pole beans. When the corn is 6–12 inches tall, sow beans 3–5 inches from the stalks.
- Add squash. About a week later, around the mound edge, so the vines run outward.
| 12.25 million | kcal of food energy per hectare |
|---|---|
| 349 kg | protein per hectare; a bean monoculture gave 175 kg |
| 13 and 16 | people a hectare could feed for a year, on energy and on protein |
6.What the trials found
These pairings have been tested in the field. The effects are real but specific: each works against one pest, under particular spacing and timing.
| Pair | Pest | Result | |
|---|---|---|---|
| Carrot with onion | Carrot fly | Fewer carrot fly attacks; the effect faded once the onions began to bulb. Uvah, I. I. I. and Coaker, T. H. (1984). |
| Lettuce with sweet alyssum | Aphids | Hover flies built up and aphids were suppressed up to 50 ft from the alyssum. UC Davis News; Smith, H. A. and Liburd, O. E. |
| Squash with Blue Hubbard border | Cucumber beetle, squash vine borer | Infestations down by up to 95% and 88%; the border must ring the crop. UConn IPM. |
| Cabbage family with thyme, onion, nasturtium or marigold | Cabbage looper, imported cabbageworm | Less caterpillar damage in Iowa studies. University of Minnesota Extension. |
| Tomato with basil or marigold | Thrips | Fewer thrips in field and greenhouse trials. University of Minnesota Extension. |
| Pepper with sunflower border | Western flower thrips | More minute pirate bugs, the thrips predator, on the peppers. Smith, H. A. and Liburd, O. E. |
| Cabbage with collard border | Diamondback moth | Collards drew the moths away from the cabbage. Smith, H. A. and Liburd, O. E. |
 | Eggplant with dill strips | Colorado potato beetle | Lady beetles and lacewings ate more beetle eggs. Smith, H. A. and Liburd, O. E. |
| Marigold before vegetables | Root-knot nematodes | Works only as a dense planting grown at least 2 months first; mixed in among crops it does not. UF/IFAS Extension ENY-056. |
How sure is each pair?
Cornell Extension calls the science of companion planting often anecdotal, and WSU horticulturist Linda Chalker-Scott says traditional charts have no scientific basis. The field-tested pairs and the documented disease and pest links are the ones to rely on; treat the rest as worth a try.
7.Pairs to keep apart
The keep-apart pairs with a real reason behind them share a disease or a pest. Others are long-standing advice that nobody seems to have tested.
- ×
Tomato and potato sound practice
Both host late blight. Infected potato tubers and tomato transplants start most outbreaks.
- ×
Strawberry and tomato, potato or pepper sound practice
Verticillium wilt builds up in the soil. Wait 5 years before planting strawberries where these grew.
- ×
Tomato and corn sound practice
Corn earworm is the tomato fruitworm. Moths move to tomatoes and peppers when corn silks brown.
- ×
Tomato family and black walnut little research
Juglone from walnut roots is blamed for poor growth, though Iowa State notes little research.
- ×
Beans or peas near onions or garlic tradition only
The best-known bad pair on every chart, yet no trials were found to support it.
Fennel and most vegetables tradition only
Traditionally planted apart. Its flowers still feed beneficial insects, so give it its own corner.
Using the chart
- Spacing, sun and water needs come first; a good pair planted too close still competes.
- Rotate plant families: do not follow tomatoes, potatoes or peppers with each other.
- Let dill, parsley and alyssum flower near crops that suffer from aphids.
- Check trap crops often and pull infested plants before pests move on.
- Treat traditional pairs as trials: keep notes and repeat what works in your garden.
Sources and notes
Pairings marked tradition only come from extension companion charts that themselves note the evidence is mostly anecdotal. Field-tested pairs and documented disease or pest links are cited individually. Spacing, sun, water and rotation matter more than any pairing.
- Cornell Cooperative Extension, Chemung County: Companion Planting fact sheet (1999)
- UF/IFAS Extension Manatee County: Vegetable Companion Planting Chart and Herb Companion Chart (herb data from the Texas Agricultural Extension Service)
- West Virginia University Extension: Companion Planting
- University of Minnesota Extension: Companion planting in home gardens
- Smith, H. A. and Liburd, O. E.: Intercropping, Crop Diversity and Pest Management, UF/IFAS ENY-862
- UF/IFAS Extension ENY-056: Marigolds (Tagetes spp.) for Nematode Management
- UC Davis News: Aphid Relief from Sweet Alyssum (UC Sustainable Agriculture Research and Education Program study)
- UConn IPM: Perimeter Trap Cropping for Yellow and Green Summer Squash
- Uvah, I. I. I. and Coaker, T. H. (1984): Effect of mixed cropping on some insect pests of carrots and onions. Entomologia Experimentalis et Applicata 36: 159–167
- Finch, S., Billiald, H. and Collier, R. H. (2003): Companion planting: do aromatic plants disrupt host-plant finding by the cabbage root fly and the onion fly more effectively than non-aromatic plants? Entomologia Experimentalis et Applicata 109: 183–195
- Mt. Pleasant, J. (2016): Food Yields and Nutrient Analyses of the Three Sisters: A Haudenosaunee Cropping System. Ethnobiology Letters 7(1): 87–98
- UF/IFAS Gardening Solutions: Three Sisters for Florida
- Chalker-Scott, L., Washington State University: The Myth of Companion Plantings
- WSU Skagit County Extension Master Gardeners (K. Wolfe, 2020): Trap Cropping
- Penn State Extension (B. K. Gugino): Tomato-Potato Late Blight in the Home Garden
- Ohio State University Extension, Ohioline PLPATH-FRU-32: Verticillium Wilt of Strawberry
- Utah State University Extension: Corn Earworm/Tomato Fruitworm
- Iowa State University Extension Yard and Garden: What plants are sensitive to the juglone produced by black walnuts?