Companion planting chart

Which vegetables, herbs and flowers to grow side by side and which to keep apart — 38 pairs, each with its reason, evidence level and sources. Where a popular pairing is folklore, the chart says so.

How to read the evidence levels

research-backed: a published trial or study measured the effect; we also say what it did not show.
practical reason: a plain reason an extension service gives: shade, support, row marking, a shared pest or disease.
tradition, little evidence: repeated in companion charts, but we found no trial behind it. The best-known ones are listed so you know what is folklore.

Left out for want of a source: tomato and asparagus, potato and horseradish, garlic and roses, dill next to tomatoes or carrots, nasturtium as a trap for cabbage pests.

All pairs

Plant	Neighbour	Together?	Evidence	Why
Basil	Tomato	good together	practical reason	Both like warmth and grow well together (Oregon State Extension). A three-year garden trial found no fewer tomato pests and no difference in taste, though beds mixed with basil used the space about 20% better on average (Bomford, 2004). [8][13]
Beet	Radish	good together	practical reason	A pinch of radish seed in the beet row comes up within days and shows where the row is; the radishes are eaten before the beets need the space (University of Maryland Extension). [12]
Bell Pepper	Sweet Corn	keep apart	practical reason	Peppers are a host of the corn earworm moth (Helicoverpa zea). When corn silks turn brown, the moths move to nearby crops to lay eggs, and Utah State Extension advises keeping peppers away from corn. [6]
Bell Pepper	Walnut	keep apart	practical reason	Peppers are among the vegetables Wisconsin Extension lists as hurt by juglone from walnut roots. English walnut releases much less than black walnut, yet a bed under any walnut also loses light and water to the tree. [4][5]
Broad bean	Cabbage	good together	practical reason	Oregon State Extension pairs cabbage-family crops with legumes such as fava beans: legumes add nitrogen to the soil, but only once their roots are left to decay — they don’t feed a neighbouring cabbage the same season (WSU). [8][11]
Broccoli	Cilantro	good together	research-backed	Flowering cilantro (coriander) attracted many hoverflies, aphid predators, beside brassica crops in a UNH Extension trial — let a few plants bloom. Whether it lowered aphids on the broccoli itself was not measured. [17]
Cabbage	Calendula	keep apart	research-backed	In a UNH Extension trial of flowers grown beside brassicas to attract beneficial insects, calendula hosted the imported cabbageworm, a cabbage pest, and drew fewer hoverflies than dill or cilantro. [17]
Cabbage	Dill	good together	research-backed	In a UNH Extension trial beside brassica crops, flowering dill drew more hoverflies — whose larvae eat aphids — than calendula, phacelia or fennel. Whether that cut aphids on the cabbages was not shown. [17]
Cabbage	Mint	good together	tradition, little evidence	Mint’s scent is said to keep cabbage pests away. WSU Extension finds that field studies don’t support aromatic plants as repellents in gardens, and Oregon State Extension says there is not enough research yet. [11][8]
Carrot	Lettuce	good together	practical reason	WSU Extension’s rule for companions is to pair root systems that don’t compete — its own example is deep-rooted carrots with shallow-rooted lettuce. [11]
Carrot	Onion	good together	research-backed	In a UK trial, rows of onions among carrots cut carrot fly attack, but only while the onions were young and leafy — once they bulbed the effect was nearly gone (Uvah & Coaker, 1984). A Finnish trial found only a slight effect (Varis, 1991). [15][16]
Carrot	Radish	good together	practical reason	Radishes come up in a few days and mark the row of slow-germinating carrots; they are pulled long before the carrots need the room (University of Maryland Extension). [12]
Carrot	Tomato	good together	practical reason	Carrots do not like heat; Oregon State Extension suggests growing them next to tomato plants, which give them shade in summer. [8]
Corn	Cucumber	good together	practical reason	Small vining cucumbers, such as pickling types, can use corn stalks as a living trellis and save space (Oregon State Extension). Heavy slicing cucumbers need a proper trellis. [8]
Corn	Green Beans	good together	practical reason	Pole beans climb corn stalks, and the two root at different depths (Oregon State Extension) — two of the ‘Three Sisters’. The beans’ nitrogen reaches the corn only after their roots decay, so corn still needs feeding (Cornell). [8][9]
Corn	Lettuce	good together	practical reason	Tall corn shades lettuce in midsummer, keeping it cooler and slowing bolting (Oregon State Extension). Sow the lettuce on the side where the corn’s shade falls. [8]
Corn	Pumpkin	good together	practical reason	In a ‘Three Sisters’ bed, broad pumpkin and squash leaves shade the soil under the corn and hold back weeds (Cornell Cooperative Extension). A root model found up to 7% more nitrate uptake in the mix; in gardens a yield gain is unproven (WSU). [9][10][11]
Corn	Tomato	keep apart	practical reason	Field corn feeds the same moth as sweet corn: corn earworm, called tomato fruitworm on tomatoes. Moths leave browning silks for nearby tomatoes (Utah State Extension); the UC Master Gardener chart also lists the pair as incompatible. [6][7]
Cucumber	Potato	keep apart	tradition, little evidence	Old companion charts, including the UC Master Gardener chart, say cucumbers and potatoes should not share a bed. No trial we found tests it; WSU Extension says such pairings are mostly folklore. [7][11]
Eggplant	Sweet Corn	keep apart	practical reason	Eggplant is on Utah State Extension’s list of crops not to grow near corn after silking: the corn earworm moth (Helicoverpa zea) then leaves the drying silks for nearby hosts. [6]
Florence fennel	Tomato	keep apart	tradition, little evidence	Fennel is often called a bad neighbour, for tomatoes too (UC Master Gardener chart). We found no garden trial that confirms it, so treat it as tradition. [7][11]
Garlic	Green Beans	keep apart	tradition, little evidence	Charts list garlic as a bad neighbour for beans (UC Master Gardener chart, after ATTRA). It is tradition: we found no trial showing that garlic harms beans. [7][11]
Garlic	Peas	keep apart	tradition, little evidence	Companion charts keep peas apart from garlic and the rest of the onion family; we could find no published trial behind it, so it is tradition rather than fact. [7][11]
Green Beans	Onion	keep apart	tradition, little evidence	Companion charts, such as the UC Master Gardener chart, say onions stunt beans. We found no trial testing it, and WSU Extension notes that most chart pairings lack evidence — treat it as tradition. [7][11]
Green Beans	Pumpkin	good together	practical reason	Beans and squash complete the ‘Three Sisters’: beans climb the corn while pumpkin covers the ground (Cornell). WSU Extension found no convincing evidence that the trio out-yields separate beds in a garden — grow it for space and tradition. [9][11]
Kohlrabi	Radish	good together	practical reason	Fast radishes mark the kohlrabi row and are pulled before the kohlrabi needs the space (University of Maryland Extension names kohlrabi among the crops to mark this way). [12]
Lettuce	Radish	good together	practical reason	Radish sown in the lettuce row marks it within days and is harvested before the lettuce fills out (University of Maryland Extension). [12]
Lettuce	Tomato	good together	practical reason	Lettuce bolts in summer heat. Oregon State Extension suggests planting it behind tall tomato plants, which shade it by midsummer. [8]
Marigold	Tomato	good together	research-backed	In UK glasshouse trials, French marigolds (Tagetes patula) grown among tomatoes from the start slowed glasshouse whitefly, through limonene in their scent. Marigolds added after whiteflies had built up did little (Conboy et al., 2019). [14]
Nasturtium	Tomato	good together	tradition, little evidence	Companion charts list nasturtium as a good neighbour for tomatoes (UC Master Gardener chart), often as a trap plant for aphids — a tradition we found no trial for. WSU Extension notes that scent-based trap crops draw insects only from about five metres. [7][11]
Nasturtium	Zucchini	good together	tradition, little evidence	Nasturtium is a traditional companion for squash and zucchini (UC Master Gardener chart). No trial we found measured a benefit, and WSU Extension says scent-based trap crops work only over short distances. [7][11]
Onion	Peas	keep apart	tradition, little evidence	Peas are traditionally kept away from the onion family in companion charts (UC Master Gardener chart), but no study we found shows harm. WSU Extension warns that such chart advice is mostly untested. [7][11]
Potato	Strawberry	keep apart	practical reason	Potatoes build up Verticillium wilt in the soil, a disease strawberries suffer from too. Penn State Extension advises against a new strawberry bed where potatoes or their relatives grew, with a 3–5 year rotation. [3]
Potato	Tomato	keep apart	practical reason	The same late blight (Phytophthora infestans) attacks both, and its spores travel on wind and rain splash. WSU Extension advises not to plant potatoes and tomatoes close together; the RHS adds a four-year rotation. [1][2]
Potato	Walnut	keep apart	practical reason	Potatoes are listed as sensitive to juglone, which walnut roots give off; the most juglone is right under the tree, where the roots are. English walnut has some juglone, far less than black walnut, so plant potatoes outside its root zone. [4][5]
Strawberry	Tomato	keep apart	practical reason	Tomatoes can leave Verticillium wilt in the soil, and strawberries catch it. Penn State Extension advises not to start a strawberry bed after tomatoes, potatoes or eggplant, and to rotate for 3–5 years. [3]
Sweet Corn	Tomato	keep apart	practical reason	Corn earworm and tomato fruitworm are one moth, Helicoverpa zea. Once corn silks dry and brown, the moths look for nearby hosts to lay eggs on, so Utah State Extension advises against planting tomatoes near corn. [6]
Tomato	Walnut	keep apart	practical reason	Walnut roots release juglone, and tomatoes are on extension lists of sensitive plants (lists based on observation, not trials). Black walnut makes the most; English walnut much less — but under its crown tomatoes also lack sun. [4][5]

Companion planting chart

How to read the evidence levels

All pairs

Neighbours by plant

Sources