Companion plants that help tomatoes thrive

The plants you grow next to tomatoes can improve their health, deter pests, and make better use of your garden space. Some companions attract beneficial insects that eat tomato pests. Others improve soil or shade the roots during hot weather. A few actually repel the insects and diseases that damage tomatoes most.

The most reliable companions are basil, carrots, marigolds, parsley, and borage. These have been grown alongside tomatoes for decades because they work—basil repels spider mites and whiteflies, marigolds deter nematodes in the soil, and borage brings in pollinators and predatory wasps that hunt tomato hornworms. Carrots and parsley take up little space and don't compete for nutrients.

Key Takeaways

  • Basil planted near tomatoes repels spider mites and whiteflies while improving the flavor of both plants when harvested together.
  • Marigolds reduce harmful root nematodes in the soil and are cheap to start from seed or buy as seedlings.
  • Borage flowers attract pollinators and parasitic wasps that hunt tomato hornworms and other large pests.
  • Avoid planting tomatoes near brassicas (cabbage, broccoli, kale) and fennel, which compete for nutrients or inhibit tomato growth.
  • Space companions 12 to 18 inches from the tomato stem to prevent root competition and allow air circulation.

Basil: the most popular tomato companion

Basil is planted next to tomatoes more often than any other companion because it works on two levels—it protects the tomato plant and improves the harvest. Basil repels spider mites, whiteflies, and some aphids by releasing compounds that these pests avoid. At the same time, basil leaves can be harvested and used fresh or dried, so you get two crops from the same garden space.

Plant basil 12 inches away from the tomato stem once both are established. Basil prefers the same warm, sunny conditions as tomatoes, so they thrive in the same bed. Water basil at the soil level rather than overhead—wet leaves invite fungal disease. Pinch off basil flower buds as they form to encourage leaf growth and keep the plant compact.

Marigolds for pest control in the soil

Marigolds are one of the few companion plants with research backing their pest-control claims. They release compounds into the soil that reduce populations of root-knot nematodes, microscopic worms that damage tomato roots and stunt growth. Plant marigolds throughout the tomato bed rather than in a single row—this spreads the protective effect across the soil.

Marigolds also attract hoverflies and other beneficial insects that eat aphids and mites. They are inexpensive to start from seed indoors six weeks before your last frost, or you can buy seedlings at any garden center. Plant them 12 to 18 inches from tomato stems. Deadhead spent flowers (pinch them off) to encourage more blooms throughout the season.

Borage: bringing in predators of tomato pests

Borage is a tall plant with blue star-shaped flowers that attract pollinators and, more importantly, parasitic wasps. These wasps lay eggs inside tomato hornworms and other large caterpillars, killing them from the inside. Borage also attracts hoverflies, which lay eggs that hatch into larvae that consume aphids and spider mites.

Borage grows 2 to 3 feet tall, so plant it on the north side of tomatoes where it won't shade them. Space it at least 18 inches away to avoid competing for water and nutrients. Borage self-seeds readily, so if you let a few flowers go to seed at the end of the season, you will have seedlings the following spring. The leaves are edible and taste like cucumber—they can be added to salads or drinks.

Carrots and parsley: space-efficient companions

Carrots and parsley occupy different soil layers than tomatoes and don't compete for the same nutrients. Carrot roots grow deep and narrow, while tomato roots spread wide and shallow. Parsley is a shallow-rooted herb that takes up minimal space. Both can be planted densely around tomato plants without slowing their growth.

Plant carrots in rows 6 to 8 inches apart around the tomato base, starting 12 inches away from the stem. Thin seedlings as they grow so mature carrots have room to develop. Parsley can be tucked into gaps between tomatoes and other companions. Both are ready to harvest in 60 to 80 days, so you can replant the space with a fall crop if your growing season is long enough.

Plants to keep away from tomatoes

Some plants actively harm tomato growth or attract the same pests. Brassicas—cabbage, broccoli, kale, and Brussels sprouts—compete with tomatoes for nitrogen and potassium. They also attract some of the same pests, so growing them nearby increases pest pressure on both crops. Fennel releases compounds that inhibit tomato growth and should be kept at least 3 feet away or grown in a separate bed entirely.

Corn attracts corn earworms, which also feed on tomato fruit and are difficult to control once established. Potatoes are susceptible to early and late blight, fungal diseases that spread easily to tomatoes. If you must grow potatoes in the same garden, space them at least 4 feet away and water at soil level only. Avoid planting tomatoes where potatoes grew the previous year.

Spacing and placement for healthy companions

The distance between tomatoes and companions matters because it affects both root competition and air circulation. Plant companions at least 12 inches from the tomato stem—closer planting increases competition for water and nutrients, especially during dry spells. Taller companions like borage should be placed on the north side of tomatoes so they don't shade the fruit during the afternoon.

Good air circulation prevents fungal diseases like early blight and powdery mildew. Crowded plantings trap moisture on leaves, especially after rain or overhead watering. Space plants so you can see soil between them, and prune lower tomato leaves once the plant is 2 feet tall to improve airflow around the base. This is more important than companion planting in preventing disease.

Frequently Asked Questions

Can I plant tomatoes next to lettuce or spinach?

Yes. Lettuce and spinach are shallow-rooted and don't compete with tomatoes for nutrients. They also prefer partial shade, which tomato foliage can provide during hot afternoons. Plant them 12 inches from the tomato stem and harvest before they get too large and dense, which would trap moisture around the tomato base.

Should I plant onions or garlic near tomatoes?

Onions and garlic are often recommended as tomato companions because they repel some pests, but the evidence is weak. They won't harm tomatoes, so if you have space and want to grow them, plant them 18 inches away. They take up little space and can be harvested independently without affecting the tomato crop.

What if I don't have room for companion plants?

Companion planting helps but is not required for tomatoes to grow. If space is limited, focus on good watering, full sun (six to eight hours daily), and removing lower leaves for air circulation. These practices prevent more problems than companions do. You can always add basil or marigolds in containers nearby if you want their benefits.

Can I plant multiple companions around one tomato plant?

Yes, but avoid crowding. A single tomato plant can support basil on one side, marigolds on another, and carrots in a ring around the base, as long as each companion is at least 12 inches from the stem. Too many plants in one spot creates dense foliage that traps moisture and reduces air circulation, which causes more disease than companions prevent.