Companion Planting Guide: What to Grow Together

March 07, 2026

Gardening is rarely a solo act. Plants influence each other in dozens of quiet ways — competing for nutrients, repelling pests, attracting pollinators, and even changing the chemistry of the soil around them. When you learn to work with these relationships instead of ignoring them, your garden becomes more productive, more resilient, and a lot more interesting.

Companion planting is the practice of intentionally placing plants near each other for mutual benefit. It’s ancient knowledge (the Three Sisters — corn, beans, and squash — have been grown together by Indigenous farmers for thousands of years) with a solid body of modern research behind it. And the best part? It works in every hardiness zone.

Why Companion Planting Works

The benefits fall into a few broad categories:

Pest confusing and repelling. Monocultures are easy targets — a pest that finds one tomato plant finds a thousand. Mixed plantings break up the visual and chemical signals that pests use to locate their hosts. Strong-smelling plants like basil, marigolds, and nasturtiums can mask the scent of your vegetables or actively repel common pests.

Attracting beneficial insects. Flowers like dill, fennel, and yarrow are magnets for parasitic wasps, lacewings, and hoverflies — all of which prey on aphids, caterpillars, and other garden pests. These are your unpaid pest management crew.

Improving soil. Legumes (beans, peas, clover) form partnerships with nitrogen-fixing bacteria in the soil, essentially manufacturing fertilizer right where you need it. Plant them near heavy feeders like corn or squash and you’re running a closed-loop nutrient system.

Maximizing space. Tall plants shade heat-sensitive crops. Sprawling plants cover bare soil and reduce weeds. Deep-rooted plants break up compaction and bring minerals to the surface for shallow-rooted neighbors.

The Classic Combinations That Actually Work

Tomatoes + Basil

This is the one everyone knows, and it earns its reputation. Basil planted nearby appears to repel aphids, spider mites, and hornworm moths. Some gardeners swear basil improves tomato flavor — the science is mixed on that, but the pest benefits are real enough to make it worth the space. Keep basil 12–18 inches from tomato stems so it gets light once the tomatoes fill out.

Also good with tomatoes: Parsley, carrots, borage (deters hornworms, attracts pollinators), and marigolds.

Keep away from tomatoes: Fennel (allelopathic to most vegetables), brassicas (they compete and attract shared pests), and corn (both attract the same earworm/fruitworm moth).

Squash + Beans + Corn (The Three Sisters)

The original companion planting system. Corn provides a trellis for beans. Beans fix nitrogen that feeds the corn and squash. Squash spreads across the ground, shading out weeds and keeping the soil cool and moist. It’s a beautiful, self-supporting system that works in zones 3–9.

How to plant: Start corn first, let it reach 6 inches, then plant beans in a ring around each stalk. Sow squash seeds between the corn rows. The timing matters — corn needs a head start or the beans will outcompete it early.

Carrots + Onions

These two protect each other. Onion flies dislike carrots; carrot flies dislike onions. Intercropping them creates a mutual-repulsion effect. Plant in alternating rows or interplant onion sets between carrot rows.

Also good with carrots: Lettuce, rosemary, sage, leeks, and tomatoes. Carrots loosen the soil as they grow, which benefits shallow-rooted neighbors.

Brassicas + Nasturtiums

Brassicas (cabbage, broccoli, kale, Brussels sprouts) are magnets for aphids and cabbage worms. Nasturtiums act as a trap crop — aphids love them, so they pile onto the nasturtiums instead of your vegetables. You can let the aphid colony build on the nasturtiums (they attract predatory insects) and simply remove them if needed. Plant nasturtiums at the edges of your brassica beds.

Also good with brassicas: Dill and chamomile (attract beneficial wasps that parasitize cabbage worms), celery, and onions. Hyssop repels cabbage moths.

Keep away from brassicas: Strawberries, tomatoes, and peppers — they compete or share pest vulnerabilities.

Peppers + Carrots + Basil

Peppers do well with a lot of partners. Carrots help break up compacted soil around pepper roots. Basil repels aphids and spider mites. Marigolds add another layer of pest deterrence. This trio makes a dense, productive planting that’s also easy on the eyes.

Lettuce + Tall Vegetables

Lettuce bolts quickly in heat. Grow it in the partial shade of taller plants — trellised cucumbers, tall pepper plants, or even sunflowers work well. The lettuce stays cooler and lasts longer into the season. This is especially useful in zones 7–10 where spring turns to summer heat fast.

Herbs That Earn Their Place Everywhere

A few herbs are so broadly beneficial they deserve a spot in almost every bed:

Marigolds — The workhorses of companion planting. French marigolds (Tagetes patula) produce a root exudate that suppresses soil nematodes; this is well-documented. Above ground, their scent confuses a range of pests. Plant them as borders around any vegetable bed or interplant throughout.

Dill — Excellent for attracting parasitic wasps and other beneficials. Let some go to flower. Note: Don’t plant mature dill near carrots (they can cross-pollinate and affect flavor) or near fennel (they hybridize easily). Young dill is fine near tomatoes; don’t let it mature and go to seed near them.

Borage — Underused and outstanding. Deters tomato hornworm, attracts bumblebees, and is edible (the flowers taste like cucumber). It self-seeds prolifically, so plant it where you’re happy to have it return.

Chamomile — A gentle accumulator plant that improves the soil around it and attracts beneficial insects. Plant a few in each bed rather than a dedicated patch.

Plants That Don’t Play Well Together

Knowing what to separate matters as much as knowing what to combine.

Keep Apart	Reason
Fennel + Almost Everything	Allelopathic — releases chemicals that inhibit most vegetables
Onions + Beans/Peas	Onions stunt legume growth
Brassicas + Tomatoes	Share pests; compete for nutrients
Potatoes + Tomatoes	Both in the nightshade family; share blight diseases
Sunflowers + Potatoes	Sunflowers are allelopathic to potatoes
Garlic/Onions + Peas	Sulfur compounds inhibit pea growth

Companion Planting by Zone

The principles stay the same across zones, but your timing and plant selection shifts.

Zones 3–5 (short seasons): Maximize space by combining quick crops with slower ones. Radishes between carrots. Lettuce under brassicas. Use nitrogen-fixing peas early in the season before beans take over.

Zones 6–7 (moderate seasons): You have the most flexibility. Full Three Sisters plantings work well. Interplant cool-season companions in spring, then swap to heat-tolerant companions (basil, marigolds, zinnia) as summer arrives.

Zones 8–10 (long, hot seasons): Shade companions are your best friends. Use tall plants to protect cool-season crops extended into fall and winter. Focus on aromatic herbs as pest deterrents since pest pressure is higher year-round.

For a full breakdown of what to plant and when in your zone, see our guide on what to plant in March by zone and our spring planting checklist.

Getting Started: Simple Companion Planting Plans

You don’t need to redesign your whole garden at once. Start with one bed and try one pairing.

Beginner bed: Tomatoes in the center, basil at 12-inch intervals around them, a ring of marigolds at the bed edge. Done. You’ll see the difference by midsummer.

Intermediate bed: Three Sisters planting in a 4×8 raised bed. Corn in a 3×3 cluster in the center (corn needs to be in a block for pollination), beans around the corn, squash filling the outer sections.

Herb border: Line your entire vegetable garden with a mix of marigolds, borage, dill, and nasturtiums. You’ve just created a pest-buffering perimeter and a habitat for beneficial insects without changing anything inside.

Tracking What Works

Keep a simple notebook or spreadsheet of what you planted where and what results you got. Companion planting effects can take a season or two to show up clearly, especially soil-building relationships. Your notes become next year’s planning guide.

For deeper planning by season and zone, the Harvest Home Guides Planting Series includes zone-specific companion planting charts and bed design templates — a great reference to keep in the garden shed.

Related Reading

• Best Companion Flowers for Vegetable Gardens
• Prepare Your Garden Soil for Spring
• Complete Herb Garden Planting Guide by Zone

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