Companion Planting: Which Vegetables Grow Better Together

This is perhaps the most famous companion pairing in the vegetable garden. Basil is thought to repel aphids and thrips — common tomato pests — through its strong volatile oils. Some gardeners also report that basil may improve tomato flavor, though the evidence for that specific claim is largely anecdotal.

What's more practical: basil attracts pollinators, and the two plants have compatible water and sunlight needs. Plant basil at the base of tomato plants or in the surrounding area. It's a low-risk pairing for beginners and makes good use of limited bed space.

The Three Sisters is a traditional Indigenous American planting system that demonstrates companion planting at its most functional. The three crops support each other in distinct ways: corn provides a vertical structure for beans to climb; beans fix nitrogen from the air into the soil, feeding the corn and squash; and squash spreads low and wide, shading the soil to retain moisture and suppress weeds.

This combination requires space — it's better suited to a larger in-ground bed or a generous raised bed than a small container setup. But if you have room, it's a genuinely effective system with a long track record.

Carrots and onions are often recommended as companions because their respective pests tend to dislike each other's scent. Carrot root fly is said to be repelled by the smell of onions, while onion fly may be deterred by carrots nearby. The evidence is more observational than laboratory-proven, but the pairing is widely practiced and low-risk to try.

Both crops are also compact and have different root depths — carrots grow deep while onions are shallow — so they don't compete heavily for nutrients underground. That makes them a space-efficient choice for a smaller bed.

Lettuce is a cool-season crop that bolts (goes to seed and turns bitter) quickly in hot sun. Planting it in the partial shade of taller plants — such as tomatoes, peppers, or trellised beans — can extend its growing season by protecting it from the harshest midday heat.

This is a practical use of vertical space and sunlight management rather than a pest or nutrient interaction. It's especially useful in summer, when unshaded lettuce can fail quickly. The taller plants don't suffer; the lettuce benefits. It's a simple efficiency win.

Marigolds — particularly French marigolds (Tagetes patula) — are a well-studied companion plant. Research has shown that they release a chemical from their roots that suppresses certain soil nematodes (tiny soil-dwelling pests that damage plant roots). They also attract hoverflies, which prey on aphids.

Interplanting marigolds throughout a vegetable bed or planting them as a border is a low-effort strategy with reasonable scientific backing. They're inexpensive to grow from seed and add visual interest. Note that they work best when planted densely and consistently — a single plant offers limited benefit.

Companion planting isn't only about beneficial pairings. Some vegetables inhibit each other's growth or compete too aggressively. A few well-documented examples worth knowing:

• Onions and beans: Onions and other alliums (garlic, leeks) are thought to stunt bean growth. Keep them separated where possible.
• Fennel and most vegetables: Fennel releases compounds that inhibit the growth of many nearby plants. It's generally best grown in its own spot or in a container away from the main bed.
• Potatoes and tomatoes: Both are in the same plant family (Solanaceae) and share diseases like blight. Growing them together concentrates that risk and makes it easier for disease to spread between them.

Being aware of these combinations is just as useful as knowing the beneficial ones. For a broader look at common mistakes new gardeners make, the garden myths guide covers some frequently misunderstood growing advice.