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Vegetables

Companion Plants for Tomatoes (And 5 to Keep Away)

Basil, marigolds, and borage earn their place next to tomatoes. Fennel, potatoes, and brassicas do not. What to plant together, and why each pairing works.

By The Grow In Backyard Team 3 min read Save to Pinterest — opens Pinterest in a new tab
Staked tomato plants heavy with ripening green fruit in a garden bed
Photo: Kolforn (Kolforn), CC BY-SA 4.0, via Wikimedia Commons
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Companion planting attracts more folklore than most gardening subjects. Some of it holds up under testing, quite a lot of it does not, and the difference matters when you are deciding what to do with limited bed space.

Here is what genuinely earns a place next to tomatoes, what to keep well away, and why.

What to plant with tomatoes

Tomato companions and what each one actually does
PlantWhat it doesHow to use it
BasilRepels thrips; disrupts moth egg-laying12–18 in away, one plant per two tomatoes
French marigoldSuppresses root-knot nematodes in soilPlant as a block the season before, then dig in
BorageDraws pollinators; deters tomato hornwormOne plant per bed corner — it gets large
NasturtiumTrap crop for aphids and whiteflyAt the bed edge, where you can pull infested leaves
Garlic / chivesSulphur compounds deter spider mite and aphidsBorder row along the bed
CarrotsUses deep soil the tomatoes are not usingBetween plants; expect smaller roots
LettuceGround cover; shades soil, holds moistureUnder the canopy, harvested before mid-summer

The honest summary is that most of the benefit is distraction and diversity, not chemistry. A bed containing five species is harder for a specialist pest to find and colonise than a block of forty identical tomato plants. That effect is real and well documented, and it is the main reason to interplant at all.

Nasturtium is a sacrifice, not a shield

Trap crops work by being more attractive than the plant you care about — so a nasturtium covered in aphids is the system working, not failing. Plant it at the edge of the bed where you can inspect it, and pull heavily infested leaves rather than spraying them.

What to keep away

Fennel is the one genuine villain. It releases allelopathic compounds from its roots that inhibit germination and stunt the growth of most neighbours, tomatoes included. Give it its own corner or grow it in a pot.

Potatoes share both early and late blight with tomatoes — they are in the same family. Planting them together turns one infection into two crops lost, and blight spores persist in the soil.

Brassicas (cabbage, broccoli, kale, cauliflower) are heavy feeders that want the same nitrogen at the same time. In a bed, the tomatoes usually lose.

Corn attracts corn earworm, which is the same insect as tomato fruitworm. Putting them together gives it two food sources and a longer season.

Black walnut is not negotiable: its roots release juglone, which is toxic to tomatoes, and the root zone extends well past the drip line. Do not plant tomatoes within 50 feet of a mature tree.

Rotate anyway

Companion planting does not replace crop rotation. Tomatoes should not go back into the same ground for three years, whatever you plant beside them — soil-borne blight, verticillium, and fusarium all build up in the bed regardless of what the neighbours are.

A layout that works

For a standard 4×8 ft raised bed:

  • Six tomato plants down the centre, 18 inches apart, staked
  • Basil between every second pair
  • Borage in two opposite corners
  • A row of garlic or chives along the long edge
  • Nasturtium trailing over the short ends
  • Lettuce underneath in spring, pulled once the canopy closes

That gives you six species in one bed, all of them either edible or working, and no two competing for the same layer of soil.

Common questions

What should you not plant next to tomatoes?

Fennel, potatoes, brassicas (cabbage, broccoli, kale), corn, and walnut trees. Fennel releases compounds that stunt neighbouring plants, potatoes share blight with tomatoes, brassicas compete heavily for the same nutrients, corn attracts the same earworm, and black walnut roots release juglone which is toxic to tomatoes.

Does basil actually improve tomato flavour?

There is no good evidence for the flavour claim. What basil does do is measurably repel thrips and confuse egg-laying moths, and it thrives in the same heat, water, and spacing as tomatoes — which is reason enough to plant it.

How close should companion plants be to tomatoes?

Close enough to share the pest-confusing effect, far enough to avoid competing for root space. Twelve to eighteen inches works for herbs and flowers; keep anything large-rooted at least two feet away.

Do marigolds really repel nematodes?

French marigolds do suppress root-knot nematodes, but only when grown as a dense cover crop and then turned into the soil the season before. A few plants dotted between tomatoes will not clear an existing infestation.

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