Companion planting — growing certain plants together so they help each other — is one of gardening's most loved ideas, and also one of its most exaggerated. Some combinations genuinely work (nasturtiums really do lure aphids away from your beans), while others are pure folklore passed down without evidence. This guide sticks to what is real.
Here are the companion combinations with the best evidence behind them, how to use each one in a real vegetable garden, and an honest look at the claims you should ignore. Written for beginners in Central and Western Europe.
| Combination | What it does | Evidence level |
|---|---|---|
| Nasturtiums + beans/brassicas | Trap crop — aphids prefer nasturtiums | Strong — widely observed |
| Marigolds (French) + tomatoes | Suppresses some soil pests; attracts hoverflies | Moderate — variety matters |
| Basil + tomatoes | Attracts pollinators; may confuse pests | Moderate — mostly beneficial habit |
| Alliums (onions/garlic) + carrots | Onion smell may mask carrots from carrot fly | Moderate — plausible, not proven |
| Flowers among veg generally | Feeds predators (hoverflies, ladybirds) | Strong — well supported |
Step 1: Start with the principle — diversity beats monoculture
The single best-supported idea in companion planting is simple: a mixed planting has fewer pest problems than a monoculture. Pests find their host plants by sight and smell; mixing things up confuses them, and flowers scattered through the veg patch feed the predators that eat pests.
You do not need a mystical chart of plant friendships. Growing flowers among your vegetables — calendula, alyssum, herbs left to flower — demonstrably brings in hoverflies, ladybirds and parasitic wasps. Our pests guide explains why this predator army is your best pest control.
Step 2: Use nasturtiums as a trap crop for aphids
This is companion planting's greatest hit, and it genuinely works: aphids prefer nasturtiums to almost everything else. Plant nasturtiums near beans, brassicas and other aphid-prone crops, and the blackfly colonies gather on the nasturtiums instead.
The technique: let the nasturtiums take the hit, then pull and bin the infested plants (or leave them as a ladybird banquet — predators follow the aphids). Sow nasturtiums direct in May; they germinate fast and flower all summer. One packet protects a whole bed.
Step 3: Plant French marigolds with tomatoes
French marigolds (Tagetes patula — not the tall African type) are the classic tomato companion. Their roots suppress certain soil nematodes, and their flowers attract hoverflies whose larvae devour aphids. The strong scent is also thought to confuse whitefly.
Plant them around the tomato bed, not in the same pots — they are companions, not competitors. Deadhead regularly to keep them flowering into autumn. Even if the pest effects are modest, a tomato bed edged with marigolds is beautiful and full of beneficial insects, which is a win on its own.
Step 4: Grow basil with tomatoes — and alliums with carrots
Basil and tomatoes are the kitchen-garden classic: they share the same sunny, rich conditions, basil's flowers feed pollinators and predators, and harvesting them together is pure joy. Whether basil measurably improves tomato flavour is unproven — but it certainly does not hurt, and the pairing is practical.
Alliums with carrots is the other famous pairing: the theory is that onion and garlic smell masks carrots from carrot fly, which finds its host by scent. It is plausible but not rigorously proven — use it as a supplement to the reliable fleece barriers, not a replacement. Interplant spring onions or garlic between carrot rows and see for yourself.
Step 5: Know what to ignore — the folklore list
Honesty time: much companion-planting advice has no evidence at all. Claims like "carrots love tomatoes" or elaborate good-neighbour/bad-neighbour charts are mostly tradition, not science. If a combination sounds magical, it probably is.
The rule: prefer mechanisms you can explain (trap crops, predator habitat, scent masking) over mystical affinities. And never let companion planting replace the basics — good soil, right watering, rotation and physical barriers do far more for your crops than any plant friendship chart.
Step 6: Design it simply — flowers in every bed
You do not need a master plan. The beginner-friendly approach: put flowers in every vegetable bed. A row of calendula at the bed end, alyssum along the edge, a nasturtium sprawling in the corner, herbs allowed to flower — this takes minutes and delivers most of companion planting's real benefits.
In raised beds, tuck companions into the corners where they do not compete. In pots, a marigold or basil in the same large container as a tomato works beautifully. Start simple, observe what happens, and expand the combinations that earn their place.
Step 7: Keep a simple record — learn what works in your garden
Companion planting is part science, part observation — and your garden is the laboratory. Keep a simple notebook: which bed got the nasturtium trap crop, whether the marigold-edged tomatoes had fewer aphids, whether the allium rows seemed to protect the carrots. A few lines per bed per season is enough.
After two or three seasons you will have something no book can give you: evidence from your own soil, your own pests, your own climate. Double down on the combinations that clearly helped, drop the ones that did nothing, and share what you learn — the best companion-planting knowledge has always been gardeners comparing notes, not charts handed down as gospel.
Troubleshooting: companion planting problems
Companions outcompeting the vegetables: The commonest real problem — vigorous nasturtiums swamping young veg. Give companions their own space at bed edges and corners, not the middle of the row, and cut them back if they get pushy.
Trap crop became a pest nursery: If you never remove or manage the nasturtiums, aphid colonies grow huge and eventually spread. Either bin heavily infested trap plants or leave them strictly as predator food — do not ignore them.
Marigolds did nothing visible: The nematode-suppression effect needs specific French marigold varieties dug in as green manure — just having them nearby is milder. They still earn their place via hoverflies and beauty.
Companions attracted slugs: Lush companion foliage is slug habitat, like any mulch. Keep companions clear of vulnerable seedlings and run your normal slug defences — see our pests guide.
What to do this October
October is planning month for next year's companions: order nasturtium, marigold and calendula seed now while choice is best, and sketch where flowers will go in each bed. Note this year's aphid hotspots — those beds get the nasturtium trap crops first.
Leave some herb flowers standing for overwintering beneficial insects, and resist tidying everything — a slightly wild autumn garden shelters next year's predator army. See the full October checklist for the month's other jobs.
Frequently asked questions
Do marigolds really repel pests?
French marigold roots suppress some nematodes (best when dug in), and the flowers attract aphid-eating hoverflies. The "repels everything" claim is overstated — but they are still one of the most useful companions.
What should never be planted together?
Honestly, very little — most "bad neighbour" warnings are folklore. The real conflicts are practical: do not let vigorous plants shade small ones, and rotate plant families yearly regardless of companions.
Can companion planting replace pesticides?
It reduces pest pressure but does not eliminate it. Think of companions as one layer — alongside predator habitat, barriers and good growing — not a magic shield.
Is the Three Sisters method (corn, beans, squash) worth trying?
It is a genuine traditional polyculture: beans feed nitrogen, corn gives support, squash shades weeds. It works, but it needs space and timing — try it once you have a season or two of basics down.
Related guides
- Common Garden Pests and How to Stop Them — the predators companions feed
- How to Grow Tomatoes at Home: Beginner's Guide — the classic companion bed
- How to Grow Herbs at Home: A Beginner's Guide — herbs are companions too
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