Companion Planting Guide: What to Grow Together and What to Keep Apart

Companion planting is one of the most discussed and least understood topics in gardening. Everyone’s heard that basil goes with tomatoes, but nobody can explain exactly why — or whether it actually matters.

Here’s what the evidence says, what works in practice, and how to plan your garden around plant compatibility.

What companion planting actually does

Good companion planting serves three purposes:

Pest management. Some plants repel specific insects. Others attract beneficial insects that eat the pests you don’t want. This is the most well-supported reason for companion planting.

Space efficiency. Pairing deep-rooted plants with shallow-rooted ones, or tall plants with shade-tolerant ones, lets you grow more in less space.

Soil improvement. Legumes (beans, peas) fix nitrogen in the soil. Growing them near heavy feeders (corn, squash, tomatoes) helps the heavy feeders access more nutrients.

What companion planting doesn’t reliably do: magically boost growth, improve flavor, or create “synergy” between plants. The internet is full of claims like “basil makes tomatoes taste better” — there’s no scientific evidence for this. What basil does near tomatoes is attract pollinators and repel certain pests. That’s useful enough.

Proven good companions

Tomatoes + basil: Basil repels aphids and hornworms, attracts pollinators. Genuinely useful.

Corn + beans + squash (The Three Sisters): The oldest companion planting system. Corn provides a trellis for beans. Beans fix nitrogen for the corn. Squash’s large leaves shade the soil, retaining moisture and suppressing weeds. This works.

Carrots + onions: Onions repel carrot flies. Carrots repel onion flies. Each protects the other.

Lettuce + tall plants (tomatoes, corn): Lettuce bolts (goes to seed) in hot sun. Growing it in the partial shade of taller plants extends the harvest.

Marigolds + almost anything: Marigolds repel nematodes and attract beneficial insects. They’re the universal companion plant. Plant them along borders or between rows.

What to keep apart

Tomatoes + fennel: Fennel secretes a substance that inhibits the growth of most nearby plants. Keep it isolated or in a pot.

Beans + onions/garlic: Onions and garlic can stunt bean growth. Plant them on opposite sides of the garden.

Potatoes + tomatoes: Both are nightshades and share the same diseases (late blight, especially). Growing them together increases disease pressure on both.

Brassicas (broccoli, cabbage) + strawberries: They compete aggressively for the same nutrients and space.

Dill + carrots: They’re in the same family and can cross-pollinate, producing poor-quality seeds. Fine if you’re not saving seed, but keep them apart if you are.

Planning around compatibility

The simplest approach:

1. List what you want to grow
2. Check compatibility pairs — which benefit each other, which hurt each other
3. Group compatible plants together in the same bed or row
4. Separate incompatible plants — different beds, or at least opposite ends of the garden

For a small garden, this is easy enough to do on paper. For a bigger garden with many varieties, you want a reference that shows compatibility at the variety level — because some varieties are more disease-resistant or pest-resistant than others, which changes the companion planting calculus.

Variety-level compatibility

Generic advice like “grow tomatoes with basil” is a good starting point, but which tomato variety? If you’re growing a variety that’s already highly disease-resistant, companion planting for pest management matters less. If you’re growing an heirloom that’s susceptible to everything, your companion choices matter a lot more.

HooGrew provides variety-level data including disease resistance, compatibility notes, and growing requirements. Search for any variety and see what it needs to thrive — from soil pH to pollination partners. Free to use, no sign-up needed.