Vegetable Companion Planting: Crop-by-Crop Pairing Guide

Companion planting works best when matched to the specific pest pressures, growth habits, and root structures of each crop. General advice (plant marigolds everywhere, never plant fennel) is a useful starting point, but knowing the best and worst neighbours for each vegetable in your garden allows you to plan beds that actively support each other through the season.

The following crop-by-crop guide covers the ten most commonly grown vegetables, focusing on companions with the strongest evidence or track record and exclusions that matter most in practice.

Tomatoes

Tomatoes' main companion requirements are aphid and whitefly deterrence, nematode suppression around the root zone, and support for the pollinators and parasitoid wasps that keep pest populations in check.

• Best companions: Basil (every 45–60 cm; VOC deterrence), French marigolds (dense border; nematodes), borage (buzz pollination, improved fruit set), nasturtiums (aphid trap crop at perimeter), parsley (parasitoid wasp support).
• Also good: Carrots (complementary root zones), sweet alyssum (beneficial insect habitat).
• Avoid: Fennel (allelopathic), potatoes (shared late blight), brassicas (different pest complexes that cross-infect), corn (shades tomatoes).

See the dedicated tomato companion plants guide for full planting layouts.

Peppers

Peppers share most companion needs with tomatoes but have specific vulnerabilities to thrips and are more susceptible to root-knot nematodes in warm soils.

• Best companions: Basil (aphid and thrip deterrence), French marigolds (nematode protection; dense border), geraniums/zonal pelargoniums (thrip trap crop — thrips colonise geraniums preferentially), carrots (root zone complementarity).
• Also good: Spinach and lettuce (cool-season ground cover in spring before peppers expand), sweet alyssum (beneficial insect support), parsley in flower.
• Avoid: Fennel, potatoes (shared Solanaceae disease vectors), brassicas.

Cucumbers

Cucumbers are heavy feeders that benefit from pollinator attraction (they need insect pollination for fruit set) and aphid management.

• Best companions: Nasturtiums (aphid trap crop), French marigolds (nematodes), dill (attracts hoverflies and parasitoid wasps), borage (pollinators), radishes (reported cucumber beetle deterrence; direct-sow at bed perimeter).
• Also good: Beans (nitrogen fixation improves soil for cucumbers if grown in the same bed in rotation), sweet alyssum.
• Avoid: Fennel, potatoes, sage (different water requirements; potential allelopathic effects on cucumbers at close range), aromatic mint-family plants that compete aggressively.

Courgettes and Summer Squash

Courgettes are large-leaved, sprawling plants that naturally suppress weeds. Their main companion needs are pollinator attraction (without adequate pollination, plants produce small, misshapen fruit) and support for managing squash vine borers and cucumber beetles in regions where these are prevalent.

• Best companions: Nasturtiums (aphid and whitefly trap crop; also attracts pollinators), French marigolds (nematodes), corn (the courgette/squash is the ground-covering element in the Three Sisters system), borage (pollinators, especially bumblebees for big courgette flowers).
• Also good: Beans (nitrogen-fixing companion in Three Sisters arrangement), sweet alyssum, phacelia for pollinators.
• Avoid: Fennel, potatoes. Avoid planting other large sprawling crops that compete for ground space — courgettes need room to spread without being impeded.

Brassicas (Cabbage, Broccoli, Kale, Brussels Sprouts)

Brassicas have a dense pest complex — cabbage white butterfly, cabbage moth, aphids, and root flies — and benefit most from trap cropping and parasitoid wasp support.

• Best companions: Nasturtiums (aphid trap crop; critical — plant before brassicas), French marigolds (root zone protection), dill (parasitoid wasps), sweet alyssum (hoverfly and wasp habitat), thyme (reported deterrence of cabbage white butterfly).
• Also good: Celery (reported to deter cabbage white butterfly through scent), spring onions (general deterrence of flying pests).
• Avoid: Tomatoes (cross-infection of different pest complexes), strawberries (brassicas reportedly inhibit strawberry growth), fennel, climbing beans (compete for vertical space; beans can shade brassicas).

Beans (French Beans, Climbing Beans)

Beans are nitrogen fixers — they host Rhizobium bacteria in root nodules that convert atmospheric nitrogen into forms plants can use. Their main companion requirement is protecting this symbiosis: alliums (garlic, onions) inhibit Rhizobium and reduce nitrogen fixation.

• Best companions: Carrots (different root zones; no competition), courgettes or squash (beans climb corn in Three Sisters; squash covers ground), nasturtiums (aphid management), sweet alyssum.
• Also good: Cucumbers (beans add nitrogen to soil), beets (different root zones; compatible).
• Avoid: Garlic and onions (inhibit nitrogen-fixing Rhizobium bacteria — this is experimentally documented), fennel, brassicas (can suppress bean root growth at very close range according to some reports).

Carrots

Carrots' primary pest is carrot fly (Psila rosae), which locates host plants by scent. Companion strategies focus on olfactory confusion — using strong-scented neighbours to disrupt the carrot fly's host-finding behaviour.

• Best companions: Spring onions or chives (alternating rows; scent confusion), leeks (similar scent disruption mechanism), rosemary (aromatic deterrence), sage.
• Also good: Lettuce (fills space between carrot rows in spring), marigolds (nematodes in heavy clay soils), tomatoes (different root zones).
• Avoid: Fennel (allelopathic to carrots — strong evidence), dill (closely related to carrots; can cross-pollinate wild carrot relatives and may compete when very young), parsnips (same pest, same soil depth, compete directly).

Note: the carrot-spring onion pairing is traditional and plausible, but field trial results are mixed. It performs better where carrot fly pressure is high; at low pressure, the effect is less visible.

Lettuce and Salad Greens

Lettuce is a cool-season crop that is often best used as a companion itself rather than having companions planted around it. Grown between warm-season transplants in spring, lettuce provides weed suppression and will have bolted and been cleared before summer crops need the space.

• Best companions: Tomatoes (lettuce in the gaps in spring — harvested before tomatoes shade it), tall brassicas (lettuce grows happily in partial shade beneath cabbage canopy), chives (reported to deter aphids from lettuce), carrots (different root depths; no competition).
• Also good: Radishes (quick-maturing; interplanted as a living mulch), spring onions, nasturtiums (at perimeter; aphid management).
• Avoid: French marigolds at very close range to young lettuce seedlings (marigold root exudates inhibit lettuce germination), fennel, parsley (some reports of allelopathic competition).

Onions and Garlic

Alliums are strong-scented plants that are often cited as broad-spectrum pest deterrents. Their main companion incompatibility is with legumes.

• Best companions: Carrots (traditional scent-confusion pairing), brassicas (reported to deter aphids and some caterpillars), roses (garlic cloves planted at the base of rose bushes are a traditional deterrent for aphids and black spot), chamomile (traditionally considered beneficial nearby).
• Also good: Tomatoes (garlic has antifungal properties that may reduce early blight risk when grown nearby), beetroot.
• Avoid: Beans, peas, and other legumes (allicin compounds in garlic and onions inhibit Rhizobium nitrogen-fixing bacteria in legume root nodules — well documented), asparagus, sage.

Potatoes

Potatoes are susceptible to several serious diseases and share some of them with other Solanaceae relatives. Their companion strategy focuses on distance from close relatives and managing Colorado potato beetle where present.

• Best companions: French marigolds (nematode suppression; particularly important in beds with repeated potato plantings), horseradish (planted at corners of the potato patch; traditional deterrent for Colorado potato beetle), nasturtiums, sweet alyssum (beneficial insect support).
• Also good: Beans (different pest complex; compatible; beans add nitrogen), coriander (attracts beneficial insects), chamomile.
• Avoid: Tomatoes (shared late blight, Phytophthora infestans; proximity accelerates disease spread), cucumbers (both heavy feeders that compete strongly), sunflowers (allelopathic compounds in sunflower roots inhibit potato growth — this is well documented), fennel, any other Solanaceae.

Beneficial Flowers for Any Vegetable Garden

These flowers improve any vegetable planting regardless of the specific crops: