What Is Companion Planting
Companion planting places crops together that benefit each other through pest deterrence, pollinator attraction, nutrient sharing, or physical support. It's not magic — there's real science behind many traditional pairings. Marigolds genuinely repel certain nematodes. Basil planted near tomatoes deters aphids and whiteflies. Tall crops like corn provide natural shade for heat-sensitive plants underneath. The goal is to create a garden ecosystem where plants support each other rather than competing.
Classic Companion Pairings
Tomatoes + Basil: Basil repels aphids, whiteflies, and certain hornworm moths. Many gardeners also report improved tomato flavor, though this is anecdotal rather than scientifically confirmed.
Carrots + Onions: The strong scent of onions deters carrot rust fly, while carrots repel onion fly. Planted together, they protect each other from their primary pests.
Squash + Corn + Beans (The Three Sisters): The oldest documented companion planting system. Corn provides a natural trellis for beans to climb. Beans fix atmospheric nitrogen into the soil, feeding the heavy-feeding corn. Squash spreads along the ground, shading out weeds and retaining soil moisture. Each plant gives something the others need.
Lettuce + Taller Crops: Lettuce bolts (goes to seed) in hot weather. Planting it in the shade of taller crops like tomatoes or trellised beans extends the harvest by keeping it cooler.
Marigolds + Everything: French marigolds release compounds from their roots that suppress root-knot nematodes, a widespread soil pest. Plant them as borders around vegetable beds. They also attract beneficial insects like hoverflies whose larvae consume aphids.
What to Keep Apart
Fennel: Inhibits growth of most nearby vegetables. Plant it in its own isolated spot or in a container.
Tomatoes + Brassicas: Tomatoes and cabbage family crops (broccoli, cauliflower, kale) compete heavily for nutrients and can stunt each other's growth.
Potatoes + Tomatoes: Both are nightshades susceptible to late blight. Planting them together increases disease pressure on both crops.
Alliums + Beans/Peas: Onions, garlic, and shallots can inhibit the growth of legumes. Keep them in separate beds.
Making It Work in Practice
Don't overthink companion planting. The biggest benefit comes from diversity itself — a varied garden attracts more beneficial insects, disrupts pest cycles, and uses space more efficiently than monoculture rows. Start by interplanting herbs throughout your vegetable beds, bordering beds with marigolds, and grouping plants with similar water and nutrient needs. Record what you plant where each season and note which combinations produce the best results in your specific garden.
For seasonal timing on when to plant these combinations, see our Seasonal Planting Calendar.