PlantLegitEvidence-based companion planting guide
Sources (1)
21 common pairings rated by what peer-reviewed studies, university extension and USDA-ARS research actually show: 7 Proven, 9 Promising, 5 Folklore-unproven. Checked 2026-10-14.
- ProvenThree Sisters: corn, beans and squashGrown together, the Three Sisters produced more total food energy and protein per area than any of the single crops or mixtures of single-crop plots in New York field trials.
- ProvenSweet alyssum with lettuce for aphid controlAlyssum flowers feed hoverflies whose larvae eat lettuce aphids; USDA-ARS found sparse alyssum plantings controlled aphids in organic romaine.
- ProvenBlue Hubbard squash as a perimeter trap crop for cucumber beetlesA ring of Blue Hubbard squash draws striped cucumber beetles away from summer squash and cucumbers, especially when the trap ring is treated.
- ProvenPush–pull: maize with Desmodium and Napier grassIn East Africa, Desmodium between maize rows repels stemborer moths and suppresses Striga weed, while border Napier grass pulls moths away.
- ProvenHairy vetch cover-crop mulch for tomatoesTomatoes transplanted into mowed hairy vetch outyielded bare soil and black plastic in USDA-ARS Beltsville trials.
Show all 21 pairings
- ProvenBlack walnut and tomatoes (avoid)Tomatoes are among the most juglone-sensitive vegetables. Do not plant them in a black walnut root zone.
- ProvenGrain sorghum as a trap crop for stink bugsUSDA-ARS found sorghum strips held southern green stink bugs and cut insecticide use in adjacent cotton.
- PromisingFrench marigold as a cover crop for root-knot nematodesGrown densely as a cover crop for at least two months where the next crop will go, marigold can suppress root-knot nematodes. Results depend on species and cultivar.
- PromisingCollards as a trap crop for diamondback moth in cabbageCollards planted around cabbage attracted diamondback moth and cut spraying, in Florida trials.
- PromisingWhite clover living mulch under cabbage and other brassicasClover living mulch reduces several cabbage pests in multiple studies, but competition often reduces head size.
- PromisingCarrots and onions against carrot flyOnions reduced carrot fly damage in one field study, but only while onions were young and when onions outnumbered carrots.
- PromisingFlowering buckwheat as an insectary stripBuckwheat flowers attract and feed many natural enemies, but proof that this lowers pest damage is inconsistent.
- PromisingGarlic and onions near aphid-prone cropsSeveral studies found garlic or onion intercrops delayed or reduced aphids on neighboring crops, likely by masking host odor.
- PromisingBasil, rosemary and other aromatic herbs vs aphidsLab and small field studies show some aromatic herbs reduce host attractiveness to aphids, but garden-level pest control is not well demonstrated.
- PromisingCoriander (cilantro) flowers to attract hoverfliesFlowering coriander attracts hoverflies and lowered aphids on cabbage, but only early in the season in one study.
- PromisingBeans or peas "feeding" nitrogen to neighbor cropsLegumes can transfer some nitrogen to neighbors in the same season, but amounts are variable and often small; most benefit comes after residues decompose.
- Folklore-unprovenMarigolds interplanted with tomatoes to stop nematodesPlanting a few marigolds among vegetables has not been shown to protect them from root-knot nematodes in field conditions.
- Folklore-unprovenTomato and basilDouble-blind taste tests found no consistent flavor benefit. Yield and pest results from the only garden-scale study are mixed.
- Folklore-unprovenTomato and Brussels sprouts ("bad neighbors")No yield advantage was found growing them together, but there is no evidence of a special antagonism either; Brussels sprouts are simply strong competitors.
- Folklore-unprovenNasturtium as an aphid trap cropWidely recommended, and plausible as a trap plant, but we found no controlled field study showing it protects nearby vegetables.
- Folklore-unprovenMint to repel garden pestsNo good field evidence that mint planted near crops repels pests. Mint oils and flowering aromatic strips are different from a living mint plant.
What the ratings mean
- Proven Consistent benefit shown in replicated field research or long-running extension trials.
- Promising Some peer-reviewed or extension evidence, but limited, conditional or mixed.
- Folklore-unproven Popular claim without supporting field evidence, or tested and not supported.
Background: WSU Extension, Gardening with Companion Plants (2023), on separating documented benefits from folklore. If evidence is mixed, the page says so.
Replacing an invasive? See native swaps by state.