Companion Planting & Interplanting

Companions create a more complex ecosystem

Monocultures — large plantings of a single crop — are easy targets for pests. Mixed plantings confuse pests with scent diversity, create habitat for predators, and reduce the spread of disease. They also use vertical and horizontal space more efficiently.

Separate fact from folklore

Companion planting has centuries of folk knowledge attached to it, not all of it well-supported. The most evidence-backed benefits are pest confusion by aromatic herbs, nitrogen fixation from legumes, and beneficial insect attraction from flowering plants. Some traditional pairings (like marigolds repelling whiteflies) have solid evidence; others are speculative.

The Three Sisters: corn, beans, squash

This Indigenous American combination is one of the most successful in garden history. Corn provides a trellis for beans; beans fix nitrogen that feeds the corn and squash; squash leaves shade the soil, suppressing weeds and retaining moisture. Plant corn first, then beans at the base, then squash around the perimeter.

Tomatoes and basil

Basil planted among tomatoes may deter aphids and thrips with its volatile oils, and the aromatic foliage can confuse pests. It also makes full use of space under and around tomato cages. Whether the repellent effect is real or not, you'll have abundant basil for cooking.

Alliums with brassicas

The strong scent of onions, garlic, and leeks can deter cabbage moths and aphids from nearby brassicas (broccoli, cabbage, kale). Interplant garlic or spring onions between brassica transplants.

Marigolds as a border

French marigolds (Tagetes patula) planted around the garden perimeter have documented evidence of repelling whiteflies and producing chemicals in their roots that kill nematodes. They also attract beneficial insects. This is one of the most well-supported companion planting practices.

Pair fast crops with slow crops

Plant quick radishes or lettuce between slow-growing plants like tomatoes or peppers. The fast crop matures and gets harvested before the slow crop needs the space, effectively doubling your yield from the same area.

Use vertical space with climbing plants

Train cucumbers, pole beans, or small melons up a trellis on the north side of your bed so they don't shade lower plants. Under the trellis, plant shade-tolerant crops like lettuce or spinach that will appreciate partial shade in summer.

Undersow with living mulch

Sow low-growing white clover or creeping thyme under taller plants. The living mulch suppresses weeds, retains moisture, attracts pollinators, and (for clover) fixes nitrogen. Cut it back occasionally to prevent competition.