Companion plants improve tomato growth and protect against pests

Planting the right neighbors next to tomatoes makes them grow stronger, taste better, and resist disease. Some plants repel the insects that damage tomatoes. Others improve the soil or shade the roots during hot weather. A few actually attract beneficial insects that eat tomato pests. The best companions are basil, carrots, marigolds, parsley, and borage — each does something different to support your tomato plant.

Spacing matters as much as the choice itself. Plant companions 12 to 18 inches away from the tomato stem so roots don't compete for water and nutrients. Tall companions like basil should go on the north side of the tomato so they don't shade the fruit. Shorter plants like marigolds can go anywhere around the base.

Key Takeaways

  • Basil planted 12 to 18 inches from tomato stems repels spider mites and whiteflies while improving flavor when both are harvested together.
  • Marigolds attract hoverflies and parasitic wasps that eat tomato hornworms and aphids, reducing the need for pest control.
  • Carrots and parsley grow below the tomato canopy without competing for light, and their roots break up soil at different depths.
  • Borage attracts pollinators and deters tomato hornworms, though it self-seeds aggressively and should be pulled back in late summer.
  • Never plant brassicas (cabbage, broccoli, kale) or fennel near tomatoes because they compete for the same nutrients and attract overlapping pests.

Basil: the classic tomato companion

Basil and tomato are planted together so often that many gardeners assume it is straightforward tradition. It is not. Basil produces oils that repel spider mites and whiteflies — two of the most common tomato pests. Plant basil 12 to 18 inches from the tomato stem, on the south or east side so it gets full sun without shading the fruit.

Basil also improves flavor when both plants are harvested together and cooked in the same dish. Pinch off basil flowers as they appear to keep the plant bushy and productive through summer. In late August, let one plant flower to attract bees, then pull it out before frost so seeds do not scatter into next year's garden.

Marigolds for natural pest control

Marigolds attract hoverflies and parasitic wasps — two insects that eat tomato hornworms, aphids, and spider mites. Plant marigolds in a ring around the tomato bed, spacing them 12 inches apart. They bloom continuously from June through frost and need only water during dry spells longer than a week.

French marigolds (the smaller varieties) work better than African marigolds for pest control because they produce stronger-smelling oils. Deadhead spent flowers every few days to keep blooms coming. Marigolds self-seed, so pull out plants in fall before they drop seeds, or expect hundreds of seedlings next spring.

Carrots and parsley for soil improvement

Carrots and parsley grow in the shade cast by tomato foliage without competing for light. Their roots reach different soil depths than tomato roots — carrots go 8 to 12 inches down, parsley stays in the top 6 inches — so they break up compacted soil and improve drainage. Plant carrots in rows 6 inches apart, and parsley in clusters of 3 to 4 plants spaced 8 inches apart.

Both take 60 to 70 days to mature, so plant them at the same time as tomatoes for a synchronized harvest. Parsley attracts swallowtail butterfly caterpillars, which are harmless to tomatoes and beautiful to watch. Thin carrot seedlings when they are 2 inches tall — the thinned greens are edible and tender.

Borage: pollinator magnet with a downside

Borage produces blue star-shaped flowers that attract bees and other pollinators, which improves tomato fruit set. The plant also deters tomato hornworms. Plant borage 18 inches from the tomato stem because it grows 2 to 3 feet tall and wide. Water it deeply once a week; borage is drought-tolerant but produces more flowers with consistent moisture.

Borage self-seeds aggressively. Pull out the entire plant in late August before flowers set seed, or you will have borage seedlings everywhere next spring. If you want borage to return, let one plant flower and drop seeds in a contained area away from the main garden bed.

Plants to keep away from tomatoes

Brassicas — cabbage, broccoli, kale, and Brussels sprouts — compete with tomatoes for nitrogen and potassium. Both crops attract similar pests, so planting them together increases pest pressure on both. Keep brassicas at least 3 feet away, or plant them in a separate bed.

Fennel produces a chemical that inhibits tomato growth and attracts the same pests. Corn and potatoes also compete for nutrients and share pests with tomatoes. Dill attracts tomato hornworms, so save dill for a bed far from tomatoes. Avoid planting tomatoes where any of these grew the previous year — move tomatoes to a new location every three years to break pest and disease cycles.

Spacing and timing for companion planting

Plant companions at the same time as tomatoes, or within two weeks of transplanting. This gives all plants time to establish roots before summer heat arrives. If you plant companions after the tomato is already 6 inches tall, the tomato will shade them and slow their growth.

Tall companions like basil and borage should go on the north side of the tomato so they do not block afternoon sun from the fruit. Short companions like marigolds and parsley can go anywhere around the base. Leave at least 12 inches between the tomato stem and any companion plant to prevent root competition. In containers, use a pot at least 18 inches wide and deep — one tomato plant with one basil plant per pot is the maximum.

Frequently Asked Questions

Can I plant multiple companions around one tomato plant?

Yes. A typical arrangement is basil on the south side, marigolds in a ring 12 inches out, and carrots or parsley filling gaps between marigolds. Space each plant 12 to 18 inches from the tomato stem. Too many plants in one spot will shade the tomato or compete for water during dry spells.

What if I plant companions too close to the tomato?

Roots will compete for water and nutrients, and the tomato will grow slower and produce less fruit. Companion plants will also shade the lower tomato leaves, increasing humidity and disease risk. If plants are already too close, thin the companions or move them 6 inches farther out.

Do companion plants work in containers?

Yes, but only one tomato and one companion per pot. Use a container at least 18 inches wide and 18 inches deep. Basil is the best choice for containers because it needs less root space than carrots or borage. Water containers daily during hot weather because soil dries faster than in-ground beds.

When should I remove companion plants?

Remove borage and basil in late August before they set seed. Carrots and parsley can stay until frost. Marigolds bloom until the first hard freeze, so leave them in place for continuous pest control. Pull all dead plants and debris in fall to remove overwintering pests and disease spores.

Can I eat the companion plants I grow with tomatoes?

Yes. Basil, parsley, and carrots are all edible. Borage flowers are edible and taste like cucumber. Marigold petals are edible but bitter — use them as garnish rather than a main ingredient. Harvest basil and parsley regularly to keep plants bushy. Carrots are ready when the shoulder is 1 inch wide.