What companion planting is
Companion planting means choosing which crops grow side by side so that they help each other, or at least don’t get in each other’s way. Some benefits are well understood: a flower that feeds the wasps that kill cabbage worms, a fast crop that is harvested before its slow neighbor needs the room, a tall plant that shades lettuce through a hot afternoon. Others are garden lore that has been copied from chart to chart for decades without anyone testing it.
This chart covers 263 plant pairings across 53 vegetables, herbs and flowers. Unlike most charts, it doesn’t treat them all as equally true.
How we grade the evidence
Every pairing gets one of four grades, based on extension publications and published research:
- Research-backed (14 pairings). Field or lab research shows an effect, at least under some conditions. The clearest example is radish as a trap crop: flea beetles prefer it, so radishes sown a little before young cabbage or broccoli draw the beetles away (UMass Amherst, WSU Extension). Dill flowers that feed parasitic wasps beside cabbage-family crops are graded the same way.
- Mixed evidence (39). Some studies find an effect, others don’t, or it only works in a narrow way. French marigolds do suppress root-knot nematodes, but University of Florida IFAS work shows it happens when they are grown densely as a cover crop for two months or more, not when a few are dotted between tomatoes. The Three Sisters is mixed too: one study found the combined planting gave more food per acre, while each crop on its own, beans especially, yielded less.
- Practical reason (122). Explained by light, space, timing, support or a shared pest or disease. Tomatoes and potatoes are a “keep apart” pair because both get early and late blight, not because of any mystery. Lettuce under tomatoes works because it is picked before the tomatoes fill the space.
- Tradition only (88). Widely repeated, but with little or no evidence behind it. The biggest group here is “aromatic repellents”: the idea that onions, garlic, thyme, sage or rosemary keep pests away by smell. Washington State University’s review of companion planting research (EM128E) found that field research hasn’t supported it.
If you only want the advice with something behind it, turn on Hide tradition-only advice at the top of the tool. Tradition-only pairings then disappear from the pair checker, the chart, the plant lists and the PDF.
Companion plants that actually work
- Radish with cabbage, broccoli and kale. Sow radishes a little before the main crop, around the bed edge, as a flea beetle trap.
- Dill, calendula and zinnias near vegetables. Small flowers feed hoverflies, lacewings and parasitic wasps whose young eat aphids and caterpillars. Let some dill and cilantro flower.
- Lettuce in the gaps. Lettuce fits between young tomatoes, peppers and brassicas and is picked before they close in. Later, the shade of taller crops slows bolting.
- Carrots with radishes. Radishes sprout in days, mark the slow carrot row and break any soil crust. They are pulled long before the carrots need the room.
- Peas or beans before corn. Peas leave nitrogen-rich roots, so sweet corn planted in the same spot afterward benefits.
- Cucumbers on something tall. Corn and sunflowers can carry light cucumber vines, and beans share a trellis line without much competition.
Just as useful is knowing what to separate. Keep the nightshades (tomatoes, peppers, eggplant, potatoes) apart and rotate them, and don’t plant strawberries where any of them grew in the last 3–4 years, because of verticillium wilt. Spread squash-family crops out, since cucumbers, melons and zucchini share cucumber beetles, mildew and bacterial wilt. Grow mint in a pot: it spreads by runners and will overrun parsley and other slower herbs.
Popular companion planting myths
- “Carrots love tomatoes.” It is the title of a well-known book, not a research finding. The two don’t compete much, which is the real reason they get along.
- Basil keeps pests off tomatoes. Only maybe. A few trials found fewer whiteflies or thrips on tomatoes grown with basil; others found no difference. They like the same heat, so grow them together anyway.
- Onions and garlic stunt beans. Repeated everywhere; we know of no study that shows it.
- Cucumbers and melons cross into strange fruit. They don’t cross-pollinate. The reason to separate them is shared pests and diseases.
- Potatoes next to cucumbers or squash cause blight. There is no shared-disease link. Both sprawl, which is the real problem.
- Herbs confuse the cabbage moth. Strong-smelling herbs haven’t held up as repellents in field trials. Mixed plantings do help a little, but any non-host plant does that.
Companion planting in a raised bed
In a 4 × 8 ft raised bed, “next to” usually means within a foot or two, so the practical reasons matter most. Put tall and trellised crops such as tomatoes, pole beans and cucumbers along the north edge, where they won’t shade the rest of the bed. Fill the south edge with low, quick crops like lettuce, radishes and spinach. Tuck calendula or zinnias into the corners, where they feed beneficial insects without taking prime space.
Spread each plant family across your beds instead of massing it in one. Four kinds of cabbage in a block concentrate cabbage worms, aphids and clubroot; mixed in with other crops, they are harder for pests to find. The same goes for squash-family crops and cucumber beetles. The square foot gardening chart shows how many of each plant fit in a square.
How to use this chart
- Check two plants. Pick Plant A and Plant B at the top. The answer says whether they are good companions, better kept apart, only paired by tradition, or have no known effect, with the reason, the evidence grade and the sources.
- See everything one plant gets on with. On a phone, the list under the checker shows every good companion and every plant to keep apart. The Plant by plant tab does the same for each plant on your chart. Tradition-only pairings are folded away; open them to see what the old charts say.
- Chart your own plants. Start from a set such as Salsa garden or Salad bed, show all 55 plants, or press Add or remove plants. Your choice is saved in this browser. Click or tap any square to check that pair.
- Read the squares. A green circle with a check means good companions, a red circle with a cross means keep apart, a dashed circle with a question mark is tradition only, and an empty square means no known effect.
- Print it. Download makes a PDF for Letter or A4 with the key and sources, or a PNG for your phone.
When you know what goes together, lay out your beds in the free garden planner, which flags bad neighbors as you plant. For corn, beans and squash, the Three Sisters garden guide covers spacing and timing.
Sources
Grades are based on these extension publications and studies. Each pairing in the chart links to the ones that apply.
- Gardening with Companion Plants (EM128E). Linda Chalker-Scott, Washington State University Extension, 2023.
- Marigolds (Tagetes spp.) for Nematode Management (ENY-056). Krueger, Dover, McSorley & Wang, University of Florida IFAS Extension.
- Trap Cropping. Washington State University Extension Master Gardener Program.
- Brassica flea beetles. UMass Amherst Vegetable Program.
- Trap cropping: a review of the state of the art. Sarkar et al., 2018 (open-access review).
- Food Yields and Nutrient Analyses of the Three Sisters. Jane Mt. Pleasant, Ethnobiology Letters 7(1), 2016.
- Vegetable Planting Guide (GardenNotes #720). Colorado State University Extension.