The best companions for tomato plants

Basil, carrots, parsley, and marigolds are the most reliable plants to grow beside tomatoes. Basil repels spider mites and whiteflies that damage tomato leaves. Carrots and parsley do not compete for the same soil nutrients, so they grow well in the same bed without slowing each other down. Marigolds attract beneficial insects and deter nematodes — microscopic pests that live in soil and feed on tomato roots.

The key to companion planting is matching plants that either help each other or at least do not harm each other. Some companions improve pest control. Others straightforward use different parts of the soil or grow at different heights, so they do not shade or starve their neighbours. A few actually improve the soil itself.

Tomatoes are heavy feeders — they pull a lot of nitrogen from the soil — so pairing them with nitrogen-fixing plants like beans or peas can help replace what the tomato takes. Onions and garlic repel spider mites and some beetles. Borage attracts pollinators and predatory wasps that hunt tomato hornworms.

Key Takeaways

  • Basil, marigolds, carrots, and parsley are proven companions that either repel pests or do not compete with tomatoes for space and nutrients.
  • Beans and peas fix nitrogen in the soil, replacing what tomatoes consume, and should be planted at the same time as tomatoes or slightly before.
  • Onions, garlic, and borage repel specific pests — spider mites, beetles, and hornworms — that commonly damage tomato plants.
  • Avoid planting brassicas (cabbage, broccoli, kale) and fennel near tomatoes because they compete for the same nutrients and can stunt growth.

Plants that repel tomato pests

Basil is the most effective pest deterrent for tomatoes. It produces oils that repel spider mites, whiteflies, and some beetles. Plant basil in the same bed or in a pot near the tomato cage — the closer the better. Basil also grows quickly and can be harvested throughout the season, so you get a practical benefit beyond pest control.

Marigolds work differently: they attract beneficial insects that prey on tomato pests, and their roots release compounds that kill root-knot nematodes in the soil. Plant marigolds around the perimeter of your tomato bed or intersperse them among the plants. They bloom all season and tolerate the same watering schedule as tomatoes.

Onions and garlic repel spider mites and some aphids. They also do not compete with tomatoes for nutrients because they pull from different soil depths. Plant them at the edge of the bed or between tomato plants — they take up little space. Garlic is planted in fall and harvested in summer, so it will be gone before your tomatoes reach full size.

Borage attracts pollinators and parasitic wasps, which lay eggs inside tomato hornworms and kill them from the inside. Borage is a tall plant with blue flowers, so plant it on the north side of your tomato bed so it does not shade the tomatoes. It self-seeds readily, so one plant can spread across seasons.

Plants that do not compete with tomatoes

Carrots and parsley grow in shallow soil and do not pull the heavy nitrogen that tomatoes need. They can be planted directly beneath or beside tomato plants without slowing either one down. Carrots are ready to harvest in 60 to 80 days, so you can replant the space with another shallow-rooted crop once they are gone.

Lettuce and spinach are also shallow-rooted and grow quickly. They mature before tomatoes reach full size, so you can harvest them and replant without disturbing the tomato roots. These leafy greens also provide some shade to the soil in hot climates, which helps retain moisture.

Chives are a mild allium that repel some pests without the strong smell of onions or garlic. They come back year after year if left in the ground, so they are a permanent edge plant for a tomato bed. Chives also attract pollinators.

Nitrogen-fixing plants that improve soil

Beans and peas have a symbiotic relationship with bacteria in the soil that convert atmospheric nitrogen into a form plants can use. When you plant beans or peas beside tomatoes, they gradually add nitrogen back to the soil as they grow. This is especially useful if you are growing tomatoes in the same bed year after year.

Plant beans or peas at the same time as tomatoes, or plant them two to three weeks earlier so they are established before the tomatoes get large. Bush beans are better than pole beans for companion planting because they stay low and do not shade the tomatoes. Peas can be trellised on the north side of the bed.

After you harvest the beans or peas, you can leave the plant material in the soil to decompose, which adds organic matter and releases the stored nitrogen slowly over the next few weeks.

Plants to keep away from tomatoes

Brassicas — cabbage, broccoli, kale, and cauliflower — compete with tomatoes for the same nutrients and can stunt both crops. They also attract some of the same pests. Keep them in a separate bed or at least 3 feet away from tomatoes.

Fennel is allelopathic, meaning it releases compounds that inhibit the growth of nearby plants. Tomatoes are especially sensitive to fennel. Do not plant fennel anywhere in a tomato bed, and keep it at least 5 feet away if possible.

Potatoes and peppers are in the same family as tomatoes (nightshades) and are susceptible to the same diseases. If one gets sick, the others are likely to follow. Separate them by at least 3 to 4 feet, or grow them in different beds entirely.

Corn is a heavy feeder like tomatoes and will compete for nitrogen. It also shades the ground heavily, which can reduce air circulation around tomato leaves and increase disease risk.

How to arrange companions in a tomato bed

Plant tall companions on the north side of the bed so they do not shade shorter plants. Basil, borage, and pole beans can go on the north edge. Tomatoes and medium-height plants like marigolds go in the middle. Shallow-rooted plants like carrots, parsley, lettuce, and chives go at the edges or between tomato plants.

Space tomatoes 24 to 36 inches apart depending on the variety. Basil can go 6 to 12 inches from the tomato stem. Marigolds can be planted 12 inches apart around the perimeter. Carrots and parsley can be sown directly in the soil between tomatoes — thin them as they grow.

If you are using containers, a 5-gallon pot can hold one tomato plant and a few basil plants or chives around the edge. Larger containers (10 to 15 gallons) can hold a tomato plant, basil, and shallow-rooted herbs like parsley or lettuce.

Timing and planting order

Plant nitrogen-fixing crops like beans and peas two to three weeks before tomatoes so they are established first. Plant basil, marigolds, and other warm-season companions at the same time as tomatoes, after the last frost date in your area. Plant carrots and parsley directly in the soil around tomatoes once they are in the ground.

If you are planting garlic, do that in fall — typically September or October in most regions — so it is ready to harvest before tomatoes are planted in spring. Onions can be planted in fall or early spring depending on your climate.

Lettuce and spinach can be planted in the same bed as tomatoes in spring, and then replanted in late summer for a fall crop after tomatoes are done producing.

Frequently Asked Questions

Can I plant basil and tomatoes in the same pot?

Yes. A 5-gallon container can hold one tomato plant and two or three basil plants around the edge. Basil roots are shallow and do not compete with tomato roots. Water regularly because containers dry out faster than garden beds, and both plants need consistent moisture.

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

Tomatoes will grow without companions, but companions reduce pest pressure and can improve soil health over time. If you have had problems with spider mites or hornworms in the past, adding basil and borage is worth the space. If pests have not been an issue, companions are optional.

What if I plant something that turns out to be a bad companion?

Pull it out. If a plant is shading the tomatoes or competing for nutrients, removing it will help the tomatoes recover. There is no penalty for experimenting — companion planting is flexible, and your garden conditions may differ from general guidelines.

Can I plant tomatoes next to herbs like oregano or thyme?

Yes. Oregano and thyme are shallow-rooted, do not compete with tomatoes, and attract pollinators. They are not as effective at repelling pests as basil, but they do not harm tomatoes and give you another harvest from the same bed.

Should I remove companion plants when I harvest tomatoes?

It depends on the plant. Remove annuals like basil and marigolds at the end of the season. Leave perennials like chives and oregano in place — they will come back next year. If you are replanting the bed with a fall crop, remove anything that will shade or compete with the new plants.