What Should You Plant Together? A Companion Planting Guide

What Should You Plant Together?
Companion planting is the practice of growing certain plants near each other because they benefit one another — repelling pests, improving soil, sharing nutrients, or simply staying out of each other's way. It's an ancient idea, and it works. But like most things in gardening, it's more nuanced than a simple checklist. So let's get into it.

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The Three Sisters: Where It All Started
If you've ever read anything about companion planting, you've heard of the Three Sisters. Corn, beans, and squash — planted together by Indigenous farmers across North America for thousands of years. It's a system so elegant it almost feels like cheating.

Here's why it works: Corn grows tall and gives the beans something to climb. Beans are legumes, which means they fix nitrogen from the air and put it into the soil — free fertilizer for the corn and squash. Squash sprawls along the ground, its big scratchy leaves shading out weeds and keeping the soil moist. Each plant does something the others can't.

If you have the space, plant a Three Sisters bed this year. Not because it's trendy, but because it genuinely produces well and barely needs you to intervene once it gets going.


Tomatoes and Basil: The Classic Duo
Ask any gardener what to plant next to tomatoes and they'll say basil. There's some debate about whether basil actually improves tomato flavor (the science is mixed), but what isn't debated is that basil repels aphids, whiteflies, and tomato hornworms. The strong volatile oils in basil leaves confuse and deter a lot of common pests.

Practically speaking, basil also loves the same conditions as tomatoes — full sun, warm temps, consistent water. They're not competing. They're coexisting peacefully while the basil does a little quiet security work on the side.

One caveat: don't let the basil flower and bolt too early, or it loses some of its repellent punch. Keep pinching the tops.


Carrots and Onions: A Mutual Defense Pact
This one is all about pests. Carrot flies are a nightmare — they lay eggs near carrot plants, and the larvae tunnel through your roots. Onion flies do the same thing to onions. But here's the twist: carrot flies hate the smell of onions, and onion flies hate the smell of carrots.

Plant them together and you've got a built-in defense system. The intermingling of scents confuses both pests enough to reduce damage significantly. It's not foolproof, but it helps — and it costs you nothing except a little planning at seed time.

Leeks work in place of onions here, too. Garlic chives are another good option if you want something that doubles as a kitchen herb.


Roses and Garlic
Roses have a pest problem. Aphids love them, Japanese beetles love them, and fungal diseases like black spot can devastate them. Garlic — planted around the base of rose bushes — repels aphids and acts as a mild fungicide. Some gardeners swear garlic also improves the fragrance of roses, though that's harder to verify.

What is consistent: garlic doesn't compete with roses for space (it grows vertically while roses spread laterally), it's easy to tuck in around existing plants, and it doubles as something you can actually eat. Win, win, and win.


What NOT to Plant Together
Companion planting is as much about avoiding bad combinations as it is about finding good ones.

Fennel and almost everything. Fennel is the loner of the vegetable garden. It produces compounds that inhibit the growth of most vegetables — tomatoes, peppers, beans, and others. Plant fennel in its own container or a dedicated corner of the garden, away from everything else you care about.

Brassicas and strawberries. Broccoli, cabbage, kale, and their relatives don't play well with strawberries. They seem to compete aggressively for nutrients, and yields from both tend to suffer. Keep them on opposite sides of the garden.

Onions and beans. Counterintuitively, while onions get along great with carrots, they're rough on beans and peas. Onions secrete compounds that stunt legume growth. Not catastrophic, but why put your beans through it?

Peppers and fennel. If fennel is the problem child of the garden, fennel near peppers is a particularly bad idea. Keep them apart.


The Underrated Companions: Flowers in the Vegetable Bed
A lot of gardeners treat the vegetable patch and the flower beds as separate kingdoms. That's a missed opportunity.

Marigolds are the all-stars of pest deterrence. French marigolds in particular produce a root secretion that kills nematodes — microscopic worms that damage plant roots and are nearly impossible to deal with otherwise. They also repel whiteflies, aphids, and Mexican bean beetles above ground. Plant them liberally throughout your vegetable garden. They're cheap, cheerful, and they work.

Nasturtiums are a companion planting secret weapon. They attract aphids like magnets — which sounds bad until you realize that means the aphids go to the nasturtiums instead of your tomatoes or beans. They function as a sacrifice plant, or a "trap crop." Let the aphids have the nasturtiums, then pull those plants and dispose of them. Your vegetables will thank you. Bonus: nasturtium flowers are edible and taste like a peppery arugula.

Borage is less commonly grown but worth knowing. It repels tomato hornworms and cabbage worms, attracts pollinators, and is said to improve the growth and flavor of tomatoes and strawberries when planted nearby. The flowers are edible and surprisingly beautiful — a vivid, star-shaped blue.


A Few Principles Worth Keeping in Mind
Before you start mapping out your beds based on companion planting charts you found online, a word of caution: a lot of the folklore around companion planting is exactly that — folklore. Some of it has solid science behind it (marigolds and nematodes, nitrogen fixation from legumes), and some of it is more anecdotal.

That's okay. Gardening involves enough uncertainty that working with probabilities and observations is just part of the deal. The goal isn't to find a perfect system; it's to stack small advantages in your favor.

Here's what actually matters:
Think about root depth. Deep-rooted plants (carrots, parsnips) coexist well with shallow-rooted ones (lettuce, radishes). They're not competing for the same layer of soil.

Think about light. Tall plants cast shade — sometimes usefully (keeping lettuce cool in summer), sometimes not (blocking sun from fruiting plants that need it). Map your sun before you map your companions.

Think about timing. Some companion relationships work partly because the plants are on different schedules. Radishes bolt and come out just as squash needs more space. That's succession planting and companion planting overlapping in a useful way.


Start Small, Pay Attention
If you're new to this, don't try to overhaul your whole garden at once. Pick one or two combinations — tomatoes and basil, carrots and onions, a border of marigolds — and observe what happens. Keep notes. Compare to previous years if you can.

Companion planting rewards attention and iteration more than any strict formula. Your garden is its own ecosystem, shaped by your specific soil, climate, pests, and quirks. Learn it, and it'll keep teaching you things for as long as you're willing to show up.

That's the thing about gardening: it never really lets you get complacent. And that's mostly what makes it worth doing.

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Nick Federoff
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