Companion planting is one of those garden topics where brilliant science and pure superstition sit side by side, often on the same list. One website swears basil makes your tomatoes taste sweeter. Another promises marigolds form a magic force field around your plants. Some of it holds up. A lot of it doesn’t.
So I’m going to do this differently. Instead of another list of forty plants that supposedly love tomatoes, I’ll walk you through what companion planting can genuinely do. Which pairings are actually backed by research, and which ones are charming garden folklore you can take or leave. Then you can plant with a clear head.
What companion planting really is
Companion planting just means growing certain plants near each other on purpose, hoping they help one another out. With tomatoes, the real, believable benefits fall into a few buckets. Pulling in pollinators and helpful predator insects, confusing or trapping pests, fixing nitrogen in the soil, and making good use of space.
Here’s the honest part most guides skip. Some of these effects are well studied and real. Many of the popular claims, especially the ones about repelling pests by smell or improving flavor, are traditional wisdom. Science either hasn’t confirmed them or has actually contradicted them. Companion planting is a nice bonus on top of good growing, not a magic wand. Keep that in mind and you won’t be disappointed.
The best companion plants for tomatoes
Let me group these by what they actually do, strongest evidence first.
Marigolds, the one with real science behind it
If you plant one thing with your tomatoes, make it French marigolds. This is the pairing with the most actual research behind it.
French marigolds fight root-knot nematodes, the microscopic soil worms that swell tomato roots and stunt the plant. The roots release a compound called alpha-terthienyl that suppresses nematodes in the soil. Studies, including work from the University of Hawaii, found tomatoes grown with or after marigolds had fewer root galls and better yields. There’s also solid evidence from a Newcastle University study, published in PLOS One. A compound in marigolds called limonene helps deter glasshouse whiteflies.
Two catches worth knowing. The nematode effect is strongest when you grow marigolds thickly in the soil as a cover crop or rotation. A token flower here and there won’t do it. And the whitefly benefit only works when the marigolds are grown right alongside the tomatoes at the same time. Plant them together and let them do their thing.
Flowers and herbs that call in the good bugs
This is the most reliable everyday benefit of companion planting: flowering plants attract pollinators and, more importantly, the predatory insects that eat tomato pests.
Herbs like basil and borage, and flowers like calendula, sweet alyssum, and parsley left to bloom, draw in bees, hoverflies, ladybugs, and lacewings. Hoverfly larvae and ladybugs devour aphids by the hundreds. A few flowers scattered through the tomato patch quietly build you a pest control crew. Borage in particular is a bee magnet and a classic tomato neighbor.
This one isn’t folklore. Attracting beneficial insects with diverse flowering plants is a well established idea. It’s the reason a mixed, flower dotted garden tends to have fewer pest blowups than a bare block of tomatoes.
Basil and the aromatic herbs
Basil is the famous tomato companion, and it earns a spot, just maybe not for the reasons you’ve heard. It flowers and pulls in pollinators, and some studies suggest it may help against thrips and hornworms, though the results are mixed.
What basil does not do, despite what half the internet says, is make your tomatoes taste better. There’s no scientific evidence for the flavor claim at all. So grow basil next to your tomatoes because they’re delicious together on a plate. Not because it sweetens the fruit.
Chives, garlic, and onions get recommended for repelling pests with their strong smell. That’s traditional wisdom with limited hard proof behind it. They won’t hurt, and they make good use of space, so plant them if you like, just hold the miracle claims loosely.
Beans and other space-and-soil helpers
A couple of pairings help the soil and the layout rather than fighting pests.
Beans and other legumes fix nitrogen from the air into the soil, which is a real, well understood process that can feed hungry neighbors like tomatoes. Nasturtiums are often grown as a trap crop, luring aphids away onto themselves and off your tomatoes. And low growers like lettuce tuck into the shady space at the base of tall tomato plants, making good use of the ground without competing much.
What to plant with tomatoes, at a glance
| Plant | What it actually does | Evidence |
|---|---|---|
| French marigolds | Suppress root-knot nematodes, deter whitefly | Strong |
| Borage, calendula, alyssum | Draw in pollinators and pest-eating insects | Strong |
| Basil | Attracts pollinators, maybe deters some pests | Mixed (no flavor benefit) |
| Beans and legumes | Fix nitrogen in the soil | Strong |
| Nasturtium | Trap crop that lures aphids away | Traditional, some support |
| Chives, garlic, onion | Claimed to repel pests by smell | Weak, traditional |
| Lettuce, low herbs | Fill space at the base, little competition | Practical |
What NOT to plant near tomatoes
Just as useful is knowing the bad neighbors. These are worth keeping apart, and the reasons here are mostly solid.
Potatoes. The big one. Potatoes are nightshades like tomatoes and share the same devastating diseases, especially late blight. Grow them close and a problem in one can wipe out both. Keep them well separated.
Other nightshades, like eggplant and peppers. Same family, same pests and diseases. You can grow them near tomatoes if you want, but you’re concentrating the risk. Keep an eye out and don’t crowd them. We dug into the pepper question specifically in can tomatoes and peppers grow together.
Brassicas, the cabbage family. Broccoli, cabbage, cauliflower, Brussels sprouts, and kale are heavy feeders that compete hard with tomatoes for nutrients. Both sides tend to sulk when planted together.
Fennel. Fennel is the classic bad companion for almost everything. It releases substances that can inhibit the growth of nearby plants, tomatoes included. Give it its own corner.
Corn. Corn and tomatoes share a pest. The corn earworm and the tomato fruitworm are the same insect, so planting them together rolls out the welcome mat.
Black walnut trees. This one is real chemistry, not folklore. Black walnuts release a compound called juglone that is toxic to tomatoes and can kill them outright. Never plant tomatoes anywhere near the root zone of a black walnut.
Mature dill. Young dill is fine and even attracts beneficial insects. As it matures it can stunt tomato growth, so keep established dill at a distance.
Does companion planting actually work?
Time for the straight answer, because you deserve one.
Yes and no. The strongest, most research backed wins are real. Marigolds against nematodes, flowering plants pulling in beneficial insects, legumes feeding the soil, and keeping disease sharing neighbors like potatoes apart. Lean into those and you’ll genuinely help your tomatoes.
But a huge amount of companion planting lore ranges from unproven to flat out contradicted by research. The flavor boosts, the smell based pest force fields, the elaborate charts of who loves whom. Treat those as harmless tradition, not gardening law.
And remember the hierarchy. No companion plant will save a tomato that’s badly watered, crowded, or diseased. Good spacing, steady watering, healthy soil, and crop rotation matter far more than which flower you tuck beside the plant. Companion planting is the cherry on top, not the cake. Our guides on planting tomatoes and heading off tomato problems are where the real gains live.
How to use companion planting well
If you want to try it, a few sensible tips.
Plant marigolds generously, not as a lone token flower. Grow them at the same time as the tomatoes for the pest benefits to kick in. Scatter a variety of flowering plants and herbs through the patch rather than in one clump. The beneficial insects end up spread where you need them. Don’t let companions crowd your tomatoes, since airflow and space still come first. And rotate where things grow each year, especially keeping tomatoes and potatoes moving around, to keep soil diseases guessing.
Do that and companion planting becomes a pleasant, low risk layer of extra help, which is exactly what it should be.
Frequently asked questions
What is the best companion plant for tomatoes?
French marigolds, by a good margin, because they have the most research behind them. They suppress root-knot nematodes in the soil and help deter whiteflies. For attracting pollinators and pest-eating insects, borage and other flowering herbs are excellent too.
What should you not plant next to tomatoes?
Potatoes and other nightshades (they share diseases like blight), brassicas like cabbage and broccoli (heavy competition), fennel (it inhibits nearby plants), and corn (shared pest). Also anything near a black walnut tree, since its juglone is toxic to tomatoes. The full list with reasons is in what not to plant with tomatoes.
Do tomatoes and basil really grow better together?
Basil attracts pollinators and may help against a few pests, so it’s a fine companion. But the popular claim that basil improves tomato flavor has no scientific support. Grow them together because they pair well in the kitchen, not for sweeter fruit.
Do marigolds really protect tomatoes?
Yes, more than most companions. French marigolds release a compound that suppresses root-knot nematodes, and research links them to fewer root galls and better tomato yields. The effect is strongest when marigolds are grown thickly in the same soil, not planted as a single token flower.
Does companion planting actually work?
Some of it, backed by real science, like marigolds against nematodes and flowers attracting beneficial insects. Much of the rest, especially flavor and smell-based pest claims, is unproven tradition. Use the proven parts, and never let companion planting replace good watering, spacing, and soil.
Bottom line: companion planting works when you stick to what’s actually been studied. Plant French marigolds for nematodes and whiteflies, add flowering herbs to pull in pollinators and pest predators, and use legumes to feed the soil. Keep potatoes, fennel, brassicas, and black walnut well away. Skip the flavor myths and the smell based force fields. Do that and your companions genuinely earn their place, alongside the real fundamentals in our complete tomato growing guide.