Companion planting
Tomato Companion Plants (and What to Keep Apart)
Good tomato companions include basil, marigold, nasturtium, garlic, onion, lettuce, and carrots. Keep tomatoes away from brassicas, fennel, potatoes, and black walnut. The proven wins are pollinator support and spacing, not magic flavor changes.
The short answer
Good tomato companions: basil, marigold, nasturtium, garlic, onion, lettuce, and carrots. Keep tomatoes apart from brassicas (cabbage, broccoli), fennel, potatoes, and black walnut. Be honest about why: the strongest, best-documented benefits are pollinator and pest support and good spacing, not magic flavor changes.
Companion planting is full of folklore. Some of it holds up. Much of it is one gardener's hunch passed down as fact. This guide separates the two, so you plant for reasons that actually work.
Plant these with tomatoes
These pairings have a concrete, sensible reason behind them. They either pull in helpful insects, deter pests, cover bare ground, or make better use of the space around a tall tomato plant.
| Companion | Why |
|---|---|
| Basil | May reduce thrips on tomatoes, and is linked to higher yields in some trials when grown about 10 inches away |
| Marigold (French) | Bright flowers draw beneficial insects and can reduce thrips; dense plantings suppress some soil nematodes |
| Nasturtium | Acts as a trap crop, pulling aphids and other pests onto itself and away from the tomato |
| Garlic / onion | Strong scent can deter some pests, and both use little ground space |
| Lettuce | Low ground cover that shades soil and uses the space under staked tomatoes |
| Carrots | Another low, narrow crop that fills the gaps without crowding the tomato canopy |
West Virginia University Extension notes that marigolds can be planted around the garden to repel insects, and that herbs and flowers help by drawing in beneficial insects and pollinators. University of Minnesota Extension adds that basil and marigolds can reduce thrip populations on tomatoes, and that basil about 10 inches from tomatoes is linked to higher yields in some trials.
Keep these apart from tomatoes
These are not superstitions. Each one has a real cost: competition, a shared disease, or a chemical that stunts the tomato.
| Avoid | Why |
|---|---|
| Brassicas (cabbage, broccoli, cauliflower) | Heavy feeders that compete with tomatoes for the same nutrients |
| Fennel | Releases compounds that inhibit many nearby plants, including tomatoes |
| Potatoes | Same family as tomatoes and share early and late blight, so the diseases spread between them |
| Black walnut | Releases juglone, which the tomato family tolerates poorly and can be stunted or killed by |
The potato warning is the one to take seriously. University of Minnesota Extension confirms that early blight pathogens infect both tomatoes and potatoes, and recommends rotating so two years pass before tomatoes return to the same spot. Planting the two side by side does the opposite of rotation.
The black walnut issue is real too. Iowa State Extension lists the tomato family among plants sensitive to juglone, the compound walnut roots release. Keep tomatoes well outside a mature walnut's root zone, or grow them in a raised bed with fresh soil.
What actually works, and what is just lore
Here is the honest split. A handful of mechanisms behind companion planting are documented. Most specific pairings are not.
Drawing in pollinators and predators works. Flowers like marigold and nasturtium feed bees and the predatory insects that eat aphids and thrips. More flowers across the season means more of these helpers. This is the best-supported reason to interplant.
Trap crops work. A nasturtium that soaks up aphids keeps them off the tomato. This is a real, studied tactic, not folklore.
Smart use of space works. Tucking lettuce or carrots under a staked tomato is just good bed design. It shades soil and grows two crops in one footprint.
The famous flavor and nematode claims are weaker. There is no solid evidence that basil makes tomatoes taste better. That one is tradition. And marigolds only suppress soil nematodes meaningfully when grown thick as a season-long cover crop, not as a few flowers in the bed.
University of Illinois Extension is direct about this. Much of what we see is not tested in a research study and is anecdotal, from gardeners who grew two plants together and felt they were companions. Even where herbs did help with pests in trials, it took many companion plants to make a lasting difference. The Three Sisters of corn, beans, and squash is one tested polyculture that genuinely works, since each plant fills a different role and layer.
Note
Much companion lore is untested. Do not bet your harvest on a chart. The safe, proven wins are simple: give every plant full spacing, plant flowers for pollinators and predators, and never pair crops that share a disease (tomatoes and potatoes being the classic mistake). Everything past that is a low-risk experiment, not a guarantee.
Spacing beats most companion tricks
A well-spaced tomato resists disease better than any companion plant can rescue it from crowding. Air moving through the leaves keeps them dry, and dry leaves do not get blight.
So before you plan an elaborate companion bed, get the tomato spacing right. Most varieties want about 18 to 36 inches between plants depending on whether they are determinate or staked. The plant spacing chart has the full crop list, and the Plant Spacing Calculator shows how many plants fit your bed.
Try it — Plant Spacing Calculator
Full calculatorExtra to cover losses (10% is typical).
You can plant
32plants
- Per row
- 8
- Rows
- 4
- Buy (incl. spare)
- 36 plants
Common mistake
Two errors undo good intentions. Overcrowding in the name of companionship packs plants so tight that air stops moving, leaves stay wet, and disease moves in. A companion that costs you airflow is a net loss. The second is planting tomatoes right next to potatoes, which share early and late blight and trade the disease back and forth. Keep them apart and rotate the nightshade family each year.
Your next step
Plant basil, marigold, nasturtium, and a low crop or two with your tomatoes for pollinators, pest control, and ground cover. Keep brassicas, fennel, potatoes, and black walnut away. Treat the rest of the companion charts as experiments, not rules.
The single biggest win is spacing. Open the Plant Spacing Calculator and lay out your tomato bed for airflow first, then read when to harvest tomatoes and pair them with the right herbs in basil companion plants.
Common questions
What should not be planted near tomatoes?
Keep tomatoes away from brassicas like cabbage and broccoli, which compete for the same nutrients, and from fennel, which can inhibit nearby plants. Do not plant tomatoes next to potatoes, since both carry early and late blight and the diseases pass between them. And keep tomatoes well clear of black walnut trees, which release juglone that the tomato family tolerates poorly.
Do marigolds help tomatoes?
Sometimes, and the evidence is partial. University of Minnesota Extension notes that basil and marigolds can reduce thrip populations on tomatoes, and marigolds draw some beneficial insects. The popular claim that a few marigolds clear root-knot nematodes is overstated. Nematode suppression takes a dense, season-long French marigold planting grown as a cover crop, not a few flowers dotted around the bed.
Can tomatoes and peppers grow together?
They can, but it is not ideal. Tomatoes and peppers are both in the nightshade family and share diseases like early blight, so planting them side by side can help those diseases spread and complicates crop rotation. If you grow them together, give each plant full spacing for airflow and rotate the whole nightshade group to a new spot each year.
Does basil help tomatoes?
The flavor claim is traditional, not proven. There is no solid evidence that basil makes tomatoes taste better. There is some research support for basil reducing thrips on tomatoes, and University of Minnesota Extension notes basil growing about 10 inches from tomatoes is linked to higher yields in some trials. Basil is a fine, harmless companion either way.
Is companion planting actually backed by science?
Some of it. Attracting pollinators and predatory insects, trap crops, and smart use of space are documented. Many specific pairings are anecdotal. University of Illinois Extension is blunt that much of what we see is not tested in research and is passed down from gardeners who grew two plants together and felt they helped. Treat charts as a starting point.
Sources
Agronomic claims in this guide are checked against these primary sources.
- Companion planting in home gardens — University of Minnesota Extension
- Companion Planting: Anecdotal or Tried and Tested? — University of Illinois Extension
- Companion Planting — West Virginia University Extension
- Early blight in tomato and potato — University of Minnesota Extension
- What plants are sensitive to the juglone produced by black walnuts? — Iowa State University Extension and Outreach
Keep reading
Pepper Companion Plants (and What to Keep Apart)
Good neighbors for peppers include basil, onions and garlic, carrots, lettuce and spinach, nasturtium, and tomatoes. Keep fennel and heavy-feeding brassicas apart. The reliable wins are spacing, pollinator support, and not crowding, not flavor magic.
Read →Basil Companion Plants (What Works and What's a Myth)
Basil grows well next to tomatoes, peppers, eggplant, and most summer vegetables, and its flowers draw pollinators when it blooms. The popular "improves tomato flavor / repels pests" claims are mostly traditional, not proven. Here is what the evidence actually supports.
Read →When to Harvest Tomatoes (Signs They're Ready)
Tomatoes are ready about 60 to 85 days after transplant, when they are fully colored and give slightly to a gentle squeeze. Here are the cues, the twist-or-cut method, and how to ripen the rest on the counter.
Read →Zucchini Companion Plants (and What to Keep Apart)
Good zucchini companions are flowers like nasturtium and borage that pull in the bees zucchini needs to set fruit, plus beans and corn. Keep zucchini away from other squash and cucumbers, which share its pests. Most "avoid" charts are folklore.
Read →Spinach Companion Plants (and What to Keep Apart)
Good spinach companions are tall shade-givers like beans and corn, quick neighbors like radishes and lettuce, and flowers for pollinators. Keep spinach from chard and beets, which share leaf miners. Most pairing rules are folklore, so plant for shade, spacing, and pest sense.
Read →Pea Companion Plants (and What to Keep Apart)
Good pea companions are carrots, lettuce, spinach, radishes, and a tall crop like corn for support. The old rule keeps peas away from onions and garlic. The honest win is cool-season timing and ground cover, not a same-season nitrogen gift to the neighbors.
Read →