Learn · Growing

Companion Planting
for Vegetables

Some plant combinations actively help each other — deterring pests, fixing nitrogen, attracting beneficial insects. Others compete or spread the same diseases. Here's what actually works.

Why companion planting works

The science behind companion planting isn't always clear-cut, but several mechanisms are well-evidenced. Understanding them helps you make sensible planting decisions rather than following folk wisdom uncritically.

Pest confusion

Strong-smelling plants like marigolds, basil, and alliums mask the scent of nearby crops. Pests navigate by smell — confusion means they move on. This is why mixed planting tends to have fewer pest problems than monoculture rows.

Trap cropping

Nasturtiums and other plants that pests prefer more than your vegetables can be planted deliberately to draw pests away. Blackfly on nasturtiums rather than your beans is a win. Remove the trap crop (and the pests on it) periodically.

Beneficial insect habitat

Flowers like dill, borage, fennel (kept away from vegetables), and phacelia attract hoverflies, parasitic wasps, and other insects that prey on common garden pests. A plot with more flowers in and around it has fewer pest problems.

Nitrogen fixing

Legumes — peas, beans, clover — fix atmospheric nitrogen into the soil through bacteria in their root nodules. Following them with hungry crops like brassicas or sweetcorn takes advantage of the nitrogen left behind when roots break down.

Ground cover

Low-growing plants like lettuce and nasturtiums planted between taller crops shade the soil, reducing moisture loss and suppressing weeds. Living mulch rather than bare earth.

Good companions and bad neighbours by crop

The combinations below are drawn from both scientific research and long-standing horticultural practice. Where evidence is stronger, it's noted.

Tomatoes 🍅

✓ Grow with
Basil
Repels aphids and whitefly. Improves flavour — possibly a myth, but the pest deterrent is real. Grow at the base of tomato plants.
Marigolds (French)
Deter whitefly and nematodes in the soil. One of the most widely proven companion plants. Plant densely around the bed perimeter.
Borage
Attracts pollinating insects and deters tomato hornworm. Also deters aphids on nearby plants.
✗ Keep away from
Fennel
Inhibits the growth of most vegetables nearby, including tomatoes.
Brassicas
Compete for nutrients and are poor neighbours for nightshades.

Brassicas 🥦

✓ Grow with
Nasturtiums
Act as a trap crop for aphids, drawing them away from brassica leaves. Also attract beneficial predatory insects.
Dill
Attracts hoverflies and parasitic wasps that feed on caterpillars and aphids on brassicas.
Celery
The strong scent is thought to confuse cabbage white butterfly and deter egg-laying.
✗ Keep away from
Strawberries
Brassicas are thought to inhibit strawberry growth.
Tomatoes
Both are heavy feeders and compete for the same nutrients.

Carrots 🥕

✓ Grow with
Leeks and onions
The classic Three Sisters pairing for roots. Leek moth deters carrot fly; carrot fly deters leek moth. Plant in alternating rows.
Rosemary
The strong scent helps mask the smell of carrots from carrot fly. Grow as a low border around carrot beds.
Lettuce
Grows low and doesn't compete with deep carrot roots. Acts as a living mulch, retaining moisture.
✗ Keep away from
Dill
Crosses with carrots (same family) and can cause poor germination if too close.
Parsnips
Same family, same pests and diseases. Don't grow adjacent.

Beans 🫘

✓ Grow with
Courgettes
The classic Three Sisters combination (with sweetcorn). Beans fix nitrogen, courgettes shade the soil, both benefit.
Sweetcorn
Beans climb the corn stalks; the beans fix nitrogen that feeds the heavy corn crop.
Summer savory
Traditionally grown with beans — thought to deter blackfly and improve yields.
✗ Keep away from
Onions and garlic
Alliums inhibit bean growth. Keep them separated by at least one bed.
Fennel
Inhibits most vegetables including beans.

Potatoes 🥔

✓ Grow with
Horseradish
Planted at the corners of a potato bed, horseradish is said to repel Colorado beetle and improve disease resistance.
Marigolds
Deter soil nematodes that can damage potato tubers. Plant between rows.
Nasturtiums
Trap crop for aphids. Keep the aphids on the nasturtiums and away from potato foliage.
✗ Keep away from
Tomatoes
Same family (Solanaceae), same diseases including blight. Never grow adjacent — disease spreads fast.
Cucumbers
Said to inhibit potato growth.

Courgettes 🥒

✓ Grow with
Nasturtiums
Trap crop for blackfly, which would otherwise colonise courgette stems and flowers.
Borage
Attracts pollinators — important for courgette fruit set, which requires insect pollination.
Sweetcorn
The tall corn provides partial shade, reducing water stress on courgettes in hot weather.
✗ Keep away from
Potatoes
Both are heavy feeders and compete for soil nutrients.
Fennel
Inhibits courgette growth.

Frequently asked questions

What is companion planting?
Companion planting is growing different plants close together for mutual benefit — typically to deter pests, attract beneficial insects, fix nitrogen, or use space more efficiently.
Does companion planting actually work?
Some combinations have strong scientific evidence — marigolds deterring nematodes, leeks and carrots mutually repelling pests, legumes fixing nitrogen. Others are more anecdotal. Use the well-evidenced ones and treat the rest as a bonus.
What should not be planted together?
Fennel inhibits most vegetables and should be kept away from the main plot. Tomatoes and potatoes should not be adjacent — same family, same blight. Onions and garlic inhibit bean growth.
What are the best companion plants for a vegetable garden?
French marigolds are the single most versatile and evidence-backed companion plant — they deter nematodes, whitefly, and aphids. Nasturtiums are excellent trap crops for blackfly. Borage attracts pollinators. Any of these grown around the edges of your plot will help.

Related guides

→ How to Plan Crop Rotation on an Allotment→ Growing Vegetables for Beginners in the UK→ Vegetable Growing Calendar for UK Growers→ Allotment Planner App

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