Companion plants improve tomato health and reduce pests without chemicals

The plants you grow near tomatoes affect how well they grow, how much they produce, and which insects move in. Some plants repel the pests that eat tomato leaves and fruit. Others improve the soil or shade the roots during hot weather. A few actually compete with tomatoes for water and nutrients and should stay away. Knowing which plants help and which hurt takes the guesswork out of garden layout.

Companion planting works because different plants have different root depths, nutrient needs, and pest enemies. A plant that attracts the natural predators of tomato hornworms, for example, reduces the number of hornworms you have to remove by hand. A plant with shallow roots won't steal water from tomato roots that go deeper. The goal is a garden where tomatoes thrive because of what grows around them, not in spite of it.

Key Takeaways

  • Basil, parsley, and marigolds planted near tomatoes repel common pests like hornworms, whiteflies, and spider mites.
  • Carrots, onions, and garlic have shallow roots that don't compete with tomato roots for water and nutrients deep in the soil.
  • Borage and nasturtium attract beneficial insects that prey on tomato pests, and nasturtium can trap aphids away from tomato plants.
  • Avoid planting brassicas (cabbage, broccoli), fennel, and potatoes within a few feet of tomatoes because they compete for nutrients or attract the same pests.
  • Plant companions 12 to 18 inches from the tomato stem to give the tomato room to grow without crowding.

Herbs that repel tomato pests and improve flavor

Basil is the most reliable herb to plant with tomatoes. It repels spider mites, whiteflies, and hornworms—three of the most common tomato pests. Basil also grows quickly and doesn't compete for space if you plant it 12 to 18 inches away from the tomato stem. The bonus: you can harvest basil leaves for cooking while the tomato plant grows.

Parsley attracts hoverflies and parasitic wasps, both of which lay eggs in or near tomato hornworms. The wasp larvae eat the hornworm from the inside, controlling the population without you having to spray anything. Parsley is a biennial, so it takes two seasons to flower and attract these insects, but it's worth the wait if hornworms are a problem in your garden year after year.

Oregano and thyme are low-growing herbs that don't shade the tomato plant and repel spider mites. Both are drought-tolerant once established, so they won't need the frequent watering that tomatoes do. Plant them at the base of the tomato cage or stake, where they'll stay out of the way.

Flowers that trap pests or attract beneficial insects

Marigolds are often recommended for tomato gardens because they repel whiteflies and some root-eating nematodes. Plant them in clusters of three or four around the tomato bed, spaced 12 to 18 inches from each tomato stem. Marigolds bloom all season and are straightforward to grow from seed, so they're a low-cost way to add pest control.

Nasturtium acts as a trap crop—aphids prefer it to tomatoes, so they congregate on the nasturtium instead. This keeps them away from your tomato leaves. Nasturtium also attracts hoverflies and parasitic wasps. Plant it on the edge of the tomato bed or in a container nearby so it doesn't shade the tomatoes as it spreads.

Borage flowers attract bees and hoverflies. The hoverflies lay eggs near tomato pests, and the larvae feed on aphids and small caterpillars. Borage is a tall plant (18 to 24 inches), so plant it on the north side of tomatoes so it doesn't cast afternoon shade. The flowers are edible and taste like cucumber, so you can harvest them for salads while the plant works for your garden.

Vegetables with shallow roots that won't compete

Carrots have roots that stay in the top 8 to 10 inches of soil, while tomato roots go much deeper. Plant carrots in rows between tomato plants or around the edge of the bed. They take 60 to 80 days to mature, so you can harvest them before the tomato plant gets very large and shades them out.

Onions and garlic also have shallow roots and repel spider mites and some soil-dwelling pests. Plant them 6 to 8 inches apart in rows, leaving 12 to 18 inches between the onion row and the tomato stem. Both are cool-season crops, so plant them in spring or fall when tomatoes are dormant, or plant them in a separate bed if you grow tomatoes year-round in a warm climate.

Lettuce and spinach grow low to the ground and mature quickly (30 to 45 days). Plant them in the shade cast by the tomato plant once it's tall enough to provide afternoon shade. This keeps the lettuce cool and extends the harvest season in hot climates. Remove the lettuce before it starts to compete for water as the tomato plant grows larger.

Plants to keep away from tomatoes

Brassicas (cabbage, broccoli, kale, and cauliflower) compete with tomatoes for nitrogen and potassium. Both crops are heavy feeders, so planting them together depletes the soil faster than either would alone. Keep brassicas at least 3 to 4 feet away from tomatoes, or grow them in a separate bed.

Fennel releases a chemical into the soil that inhibits the growth of many plants, including tomatoes. It's allelopathic, meaning it actively suppresses nearby plants rather than just competing for resources. Don't plant fennel anywhere in the tomato bed or within a few feet of it.

Potatoes are in the same plant family as tomatoes (Solanaceae) and attract the same pests and diseases. If you grow potatoes and tomatoes in the same garden, keep them at least 4 to 5 feet apart. Better yet, grow them in different beds or in different seasons to break the pest cycle. Peppers and eggplants are also in this family, so space them away from tomatoes too.

Corn grows tall and casts heavy shade. It also attracts hornworms, the same pest that eats tomato leaves. If you grow corn, plant it on the north side of the garden where it won't shade tomatoes, or grow it in a separate area.

How to arrange companion plants in the tomato bed

Start with the tomato plant in the center or along a trellis. Measure 12 to 18 inches out from the stem in all directions—this is the zone where you can plant shallow-rooted companions like carrots, onions, and lettuce without crowding the tomato roots. Plant herbs like basil and oregano in this zone too, since they stay small and won't shade the tomato plant.

Place taller companions like borage and nasturtium on the north side of the tomato, where they'll get morning sun but won't cast afternoon shade on the tomato leaves. Marigolds can go anywhere in the bed, but clustering them in groups of three or four is more effective than scattering single plants.

Leave space between companion plants so air can circulate. Crowded plants trap moisture and encourage fungal diseases. If you're using a tomato cage, plant companions outside the cage perimeter. If you're using a stake or string trellis, plant companions to the sides rather than directly beneath the tomato canopy.

Timing: when to plant companions with tomatoes

Plant basil, marigolds, and nasturtium at the same time you plant tomatoes, or a week or two after if you're starting from seed. These plants grow quickly and will be established by the time pests arrive in mid-summer. If you're planting tomato seedlings from a nursery, you can plant basil seedlings at the same time.

Sow carrot and lettuce seeds directly in the soil around the tomato plant once it's 6 to 8 inches tall and the soil has warmed. This gives the tomato a head start so it won't be shaded out by the companion plants. Plant onions and garlic in fall (in cool climates) or early spring, before you plant tomatoes, so they're established when the tomato goes in.

Parsley takes a long time to germinate (two to three weeks) and grow, so start it indoors 6 to 8 weeks before your last frost date, or buy seedlings from a nursery. Plant it out at the same time as tomatoes so it has the whole season to establish and attract beneficial insects.

Frequently Asked Questions

Can I plant basil and tomatoes in the same pot?

Yes, if the pot is at least 5 gallons. Plant the tomato in the center and basil around the edge, 6 to 8 inches away from the tomato stem. Water regularly because container soil dries out faster than garden soil. Pinch off basil leaves as it grows to keep it from shading the tomato plant.

Do I have to plant companions, or will tomatoes grow fine alone?

Tomatoes will grow without companions, but companion plants reduce pest damage and can increase yield. If pests are a problem in your garden, companions are worth trying. If you've never had pest issues, you may not need them.

What if I plant something that turns out to compete with tomatoes?

Pull it out as soon as you notice the tomato plant is struggling—yellowing leaves, slow growth, or wilting despite regular watering. Don't wait to see if it improves. Removing the competing plant quickly gives the tomato a chance to recover.

Can I plant tomatoes near mint?

Mint spreads aggressively through underground runners and will take over a garden bed. Plant it in a pot or a separate raised bed, not in the ground near tomatoes. If you want mint nearby for cooking, keep it contained.

Should I plant the same companions every year?

Rotating companions is a good idea if you've had pest or disease problems. If hornworms were bad last year, plant parsley this year to attract parasitic wasps. If you had fungal disease, focus on companions that improve air circulation. Rotating also prevents any one companion from depleting specific nutrients year after year.