Eating Garden

A quick answer from the garden notebook

Companion Planting for Tomatoes

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Short answer

The best companions for tomatoes are basil and French marigolds. In studies, they cut thrips and whiteflies. Lettuce and spinach can share the bed while the tomatoes are small. Keep tomatoes away from potatoes, sweet corn and black walnut trees.

Tomato companions, with the evidence

Some of this is measured in trials and some is long-standing garden practice. Each note below says which it is.

Good together

Trials show a real benefit:

  • French marigoldIn large greenhouse trials, French marigolds grown beside tomatoes all season slowed whitefly build-up; adding them after an outbreak helped little.Measured in trials
  • BasilStudies found basil grown with tomatoes reduced thrips, and growing basil between tomatoes may also help the tomatoes grow.Measured in trials

Extension programs recommend this pairing:

  • LettuceLettuce can grow under and between tomato plants, using ground the tomatoes have not filled yet.Recommended by extension programs
  • SpinachSow spinach early, then set tomato transplants into the same bed; the spinach is picked as the tomatoes fill in.Recommended by extension programs

Gardeners have long paired these:

  • Nasturtium or pot marigold (calendula)Gardeners often plant these flowers near tomatoes hoping to attract pest-eating insects; the benefit is a hope, not a tested result.Traditional garden practice

Keep apart

Extension programs advise keeping these apart:

  • PotatoTomatoes and potatoes both get late blight, so extension advice is not to plant them close together.Recommended by extension programs
  • Black walnut treeBlack walnut roots release juglone, which harms tomatoes, so keep tomato beds away from walnut root zones.Recommended by extension programs
  • Sweet cornCorn earworm is the same insect as tomato fruitworm, and when corn silks turn brown the moths move to nearby tomatoes.Recommended by extension programs

Plant marigolds early, not as a rescue

In a 2019 greenhouse study, French marigolds grown next to tomatoes all season slowed the growth of whitefly numbers. Marigolds added after the whiteflies came helped very little. Minnesota Extension also reports studies where basil and marigolds cut thrips on tomatoes.

Why potatoes, corn and walnuts stay away

  • Potatoes: both crops get late blight. Washington State Extension says not to plant them close together.
  • Sweet corn: the corn earworm is the same insect as the tomato fruitworm. Utah State Extension says the moths move to tomatoes nearby once the corn silks turn brown.
  • Black walnut: its roots give off a substance that harms tomatoes. Wisconsin Extension says to keep tomatoes away from walnut roots.

Use the space under young tomatoes

Lettuce can grow under and between tomato plants while they are small. Minnesota Extension also suggests sowing spinach early. Set the tomato plants into the same bed, then pick the spinach as the tomatoes fill in.

What popular lists get wrong

Many lists say marigolds protect the whole garden. UMass Extension says their main proven benefit is against root nematodes, tiny worms in the soil. That only works when marigolds are grown as a cover crop and dug into the soil. Washington State Extension adds that French marigolds also keep away helpful insects, not just pests.

Sources

The full growing guide

  • Tomato

    A warm season fruit that almost everyone treats as a vegetable, and the crop most people try first. It needs heat, steady water and something to lean on.

    Harvest
    50 to 85 daysfrom transplant
    Effort
    Season
    Warm

More tomato questions

  • When to Plant Tomatoes

    When to plant tomatoes depends on your last spring frost: set plants out 1 to 3 weeks after it, once the soil has warmed.

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