What are good companion plants for tomatoes

Companion Herbs for Tomato Gardens

Worst Tomato Companion Plants

These plants are infamous for inhibiting tomato plant growth and increasing their susceptibility to pests or diseases and should not be planted with tomatoes.

• Cabbage (Brassica) family: Relatives of cabbage cultivars stunt the growth of tomato plants (including broccoli, Brussels sprouts, cabbage, cauliflower, collards, ornamental kale, kohlrabi, rutabaga varieties, and turnip). However, some gardeners do like placing collard greens a few feet away from their tomato plants to lure away damaging harlequin bugs.
• Sweet Corn: The corn earworm is the same as the tomato fruitworm (Helicoverpa zea). Growing plants in proximity that are susceptible to the same pests can invite disaster and a decimated garden.
• Eggplant, hot peppers, and heirlom potatoes: These plants are in the nightshade family like tomatoes, and are all susceptible to early blight and late blight, which can build up in the soil and get worse each year. Avoid planting them near each other or in place of each other for at least three years. Tomato hornworms (Manduca quinquemaculata, the larva stage of the five-spotted hawkmoth) love the foliage and fruit of tomatoes, peppers, and eggplants and can quickly decimate plants. Also, planting tomatoes near potatoes can make the potatoes more susceptible to potato blight.
• Fennel: Fennel secretes a substance from its roots that inhibits tomato plant growth. This secretion affects many other garden plants, too. However, some gardeners deploy fennel to manage aphid invasions.
• Walnuts: Do not plant tomatoes under walnut or butternut trees, which produce an allelopathic chemical called juglone that inhibits the growth of tomatoes (and all the members of the nightshade family). Tomatoes are also susceptible to the disease walnut wilt.

Tomatoes and Roses

While several plants are touted as terrific tomato companions, tomatoes can act as companion plants, too. Tomatoes have been shown to protect flowering roses from a disease called black spot.

If you can't plant tomatoes among your roses, make a spray of liquefied tomato leaves, a tablespoon of cornstarch, and about 4 pints of water. Spritz your roses once a week to keep black spot at bay.

Great Companion Plants for Roses

Article Sources

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1. Cover Crops. USDA.

2. Pest Control Companion Planting Chart. Brigham Young University. 

3. Phytophthora Blight. University of Massachusetts Vegetable Extension Program.

4. Baker, Brian P. and Grant, Jennifer A. Garlic and Garlic Oil Profile. New York State Integrated Pest Management. Cornell University.

5. Companion Planting Chart. University of California Cooperative Extension.

6. Gardening: It’s a Risky Business. Mississippi State University Extension, 2019. 

7. Gevens, Amanda; Seidl, Anna; Hudelson, Brian. Late Blight. University of Wisconsin-Madison Extension, 2017.

8. Bauske, Mitchell J.; Robinson, Andrew P.; Gudmestad, Neil C. Early Blight in Potato. North Dakota State University, 2018. 

9. Herb Gardening. Colorado State University Extension.

10. Walnut Wilt. Kansas State University Research and Extension, 2022.

11. Gray, Laveryne. Companion Plantings: Tomatoes and Roses. Marion County Master Gardeners.  

22 Science-based Plant Partners for Tomatoes

Have you wondered if there are plants you can grow side by side with your tomatoes to maximize harvests and grow healthier plants? You’ve probably heard of companion planting before. Maybe you know gardeners who swear by it. Or maybe you’ve heard that it doesn’t actually work. Old-school companion planting was deeply rooted in folklore and conjecture with little to no science to back it up. As a horticulturist, I’ve always had a hard time believing in the merits of traditional companion planting. However, thanks to research for my newest book, I look at the practice a bit differently these days. Today, I’d like to open your eyes to a more modern, science-based approach to companion planting and then introduce 22 tomato companion plants that are proven to help grow healthier, more productive tomatoes.

A new kind of companion planting

In writing my book, Plant Partners: Science-based Companion Planting Strategies for the Vegetable Garden (Storey Publishing), my goal was to look at companion planting through a science lens. I wanted to sort through current university and agricultural research that looks at the possible benefits of partnering plants and then put it all together into a book to help gardeners make smart planting decisions.

In the research community, plant partnering isn’t called companion planting (probably because of the term’s questionable reputation). Instead, it’s known as interplanting, intercropping, or creating a polyculture. But no matter what you call it, there’s some fascinating scientific research out there that looks at ways we can combine plants together to gain a benefit. Sometimes the partnerships consist of two plants grown near each other. Other times, the plants are planted in succession with one another (one crop after another in the same space). And still other times, it’s more about planting a plethora of plants together to create a diverse, more resilient growing environment.

The benefits of companion planting

While controlling pests is probably the most popular goal gardeners are trying to achieve by partnering certain plants together, there are many other benefits to companion planting. Did you know that some types of companion planting can also reduce weed or disease pressure in the garden? In addition, certain plant combinations can improve soil fertility or structure, enhance pollination, or encourage pest-eating beneficial insects. In the book, I look at hundreds of studied plant partnerships aimed at achieving these goals, but today, let’s keep it simple and focus on companion plants that meet one or more of these goals for the world’s most popular garden crop: the tomato.

Tomato companion plants

The 22 tomato companion plants featured below are categorized by the benefits they achieve, starting with partnerships for pest reduction and moving on from there. I offer basic details on each partnership so you can start using these companion plants today, but if you want more details on each combo, I encourage you to check out Plant Partners.

Tomato Companion Plants for Pest Control

The following tomato companion plants are aimed at managing pests in the vegetable garden. Some of these combinations act to disrupt a pest’s egg-laying behaviors, while others are meant to serve as a sacrificial trap crop to lure pests away from your tomato plants.

1. Thyme (Thymus vulgaris):

If yellow-striped armyworms are problematic in your garden then thyme is a great choice among tomato companion plants. Researchers at Iowa State found that interplanting tomatoes with thyme (or basil) resulted in a reduction in egg-laying by adult armyworms. Thyme makes a great living mulch around tomato plants. Just keep in mind that it’s perennial, so the plants will have to be moved when tomato plants are rotated to a new garden spot each season.

2. Cowpeas (Vigna unguiculata):

Cowpeas are a favorite of the southern green stink bug. Because of this, a nearby planting of cowpeas lures green stink bugs away from your tomato crop, saving it from significant damage. Primarily problematic in the Southern US, green stink bugs feed on many different fruits and veggies, causing stipping and corking of the flesh. Plant cowpeas several feet away from tomatoes (stinkbugs are good fliers) and sow them several weeks before planting your tomatoes.

3. Radish (Raphanus sativus): 

Plant radish around the base of your tomato plants to lure flea beetles away. Flea beetles don’t move very far, so for these tomato companion plants to work, they must be immediately adjacent to your tomatoes. Flea beetles much prefer radish foliage to tomatoes and will chew ragged holes in the radish leaves instead of destroying young tomato plants. Mature tomato plants can withstand a good bit of flea beetle damage, but young transplants can really suffer. Pac choi makes another excellent sacrificial trap crop for flea beetles.

4. Collards (Brassica oleracea var. viridis):

If harlequin bugs attack your tomatoes every season, then this companion planting strategy is for you. Harlequin bugs are most prevalent in warm regions of the US, but their range is expanding northward. They favor plants in the cabbage family (cole crops) and can be lured away from tomatoes (and even other cole crops) by planting collards nearby. These bugs produce several generations per year, so plant your sacrificial collards several weeks before planting your tomatoes and place them around the periphery of the garden, several feet away from the plants you want to protect.

5. Basil (Ocimum basilicum):

Not only is basil a great tomato companion on a plate, it’s also one of the most important tomato companion plants for the garden, most notably when it comes to deterring thrips and tomato hornworms. While traditional companion planting may tell you this is because the scent of basil drives away these pests, this likely isn’t the case. More recent research is indicating it works because the volatile chemicals (odors) released by basil plants mask the scent of tomato plants, making it harder for these pests to find their host plant. On tomatoes, thrips transmit tomato spotted wilt virus and cause stunted growth and stippling on the fruits. Hornworms eat the foliage of tomato plants, leaving only the stems behind. Interplanting tomatoes with basil has been shown to limit egg-laying behaviors of the adult hornworm moths and to limit damage from thrips.

Tomato Companion Plants to Increase Beneficial Insects

Biocontrol is the practice of attracting, supporting, and even releasing beneficial insects into the garden to help manage pests. There are tens of thousands of species of predatory and parasitoidal insects that naturally keep pest populations in check in our gardens. Frankly, there’s no need to purchase and release beneficial insects when you can simply provide the resources needed by the good bugs already living in your yard. Since most beneficial insect species need both the protein found in their prey and the carbohydrates found in nectar at some point in their lifecycle, some of the best tomato companion plants provide these insects with this much needed nectar. Having these resources available encourages the good bugs to stick around and help manage pests.

6. Dill (Anethum graveolens):

The tiny flowers of dill supply nectar and pollen to many different beneficial insects, including ladybugs, lacewings, minute pirate bugs, parasitic wasps, tachinid flies, and more. For tomatoes, tiny parasitic wasps feeding on dill blossoms also lay eggs in tomato hornworms, tomato fruit worms, and other pest caterpillars. Always have plenty of dill in the garden and allow it to go to flower to help encourage beneficials.

7. Fennel (Foeniculum vulgare):

Similar to dill, the small flowers of fennel provide nectar for a diverse array of beneficial insects. I often find the eggs of predatory lacewings clinging to my fennel leaves. Of particular importance to tomatoes are the parasitic aphidius wasps that use aphids to house and feed their developing young. Aphids can become problematic on tomato plants and interplanting with fennel could help limit their numbers.

8. Oregano (Origanum vulgare):

Another important herb to include in your tomato patch, oregano doesn’t just taste good, it’s also one of the best tomato companion plants. But for oregano to do its job, you have to let it go to flower. Oregano plants and flowers support many different pest-eating beneficial insects.

9. Cilantro (Coriandrum sativum):

In the same plant family as dill and fennel, the blooms of cilantro are yet another valuable nectar source for the predatory insects that consume many common tomato pests. Grow it in and around your garden and be sure to let it go to flower after you’ve made a moderate harvest.

10. Sweet alyssum (Lobularia maritima):

Most studied for its use in improving biological control on lettuce farms, sweet alyssum is another favorite among tomato companion plants. Its small white blooms are an exemplary food source for both the syrphid flies and parasitic wasps that help manage aphids. I won’t grow tomatoes without a “skirt” of alyssum beneath them!

Tomato Companion Plants for Weed Control

These plant partnerships are aimed at minimizing weeds. The first three involve using cover crops and living mulches. The fourth uses another common veggie as a weed-reducing companion plant for tomatoes.

11. Winter rye (Secale cereale):

This cover crop is on this list of tomato companion plants for its ability to reduce weeds around tomato plants. Winter rye contains some 16 different allelochemicals (compounds produced by some plants that restrict the growth of neighboring plants). It is one of the most commonly studied and utilized examples of a cover crop that can help limit weed growth. The allelochemicals found in winter rye prevent weed seed germination, but they do not harm transplants of tomatoes, peppers, eggplants, and other veggies that are grown in the residue left behind after cutting down the cover crop. For this plant partnership, sow rye in the fall as a winter cover crop. When spring arrives, mow the plants down to the ground just as they are coming into flower (don’t cut them too soon or they’ll re-sprout, and don’t wait too long or they’ll drop seeds). Leave the residue in place and plant your transplants right through it. No need to disturb the soil by tilling.

12. Oats (Avena sativa):

Oats are the perfect cover crop for beginners. They are winter-killed in climates with regular freezing temperatures, and in the spring, you can plant your tomatoes right through the residue. Fall-planted oats help control weeds by protecting the soil through the winter and early spring, forming a mat that’s impenetrable to weeds. Plus, as the debris decomposes, it adds organic matter to the soil.

13. Crimson clover (Trifolium incarnatum):

When grown as a living mulch, crimson clover serves as one of the best tomato companion plants. Plant it in between tomato rows or in between tomato plants and let it grow all season long. Not only will it outcompete weeds, since it is a legume, it will also provide nitrogen to the soil and nearby plants through nitrogen fixation. Sow crimson clover seeds in spring or fall for a living mulch around tomatoes. Mow, weed whack, or cut back the clover several times a year to restrict its growth and return the nutrients in its cut off shoots back to the soil. Crimson clover also supports high densities of beneficial insects and pollinators. Always cut it back before the plant drops seed. Crimson clover is winter killed where winter temps regularly dip below 0°F.

14. Cucumbers (Cucumis sativus):

You might be surprised to learn that cucumbers also produce several growth-inhibiting allelochemicals, cinnamic acid being the most studied. Cucumbers can be used as a weed-management tool when grown as a thick groundcover of living mulch around taller crops, like corn, tomatoes, and okra. They also act to shade weed seeds and reduce germination. Don’t use them if you’re growing partner crops from seed, but they’re perfect tomato companion plants because you’re starting with transplants instead of seeds.

Tomato Companion Plants to Reduce Disease

These tomato companion plants have been found to reduce fungal diseases, sometimes in unique ways. The first two are used as standard garden crops while the second two are used as cover crops.

15. Sweet Potatoes (Ipomoea batatas):

When it comes to tomato companion plants, sweet potatoes are tops for reducing diseases. No, they don’t provide some cool disease-fighting compound, instead they shield the tomato plants from the “splash up effect” and keep fruits off the ground. The spores of many fungal diseases, including Septoria leaf spot and early blight, live in the soil. When raindrops hit the soil and splash up onto the tomato leaves, the fungal spores travel with them, infecting the plants. By growing a dense cover of sweet potatoes over the soil around tomato plants, the splash up effect is reduced. Combining this partnership with the use of a cover crop whose residue is left in place, was shown to be even better for reducing disease transmission via the splash up effect.

16. Bush Beans (Phaseolus vulgaris):

This plant partnership reduces diseases by increasing air circulation. Since fungal disease spores thrive in damp, humid conditions, interplanting tall tomato plants with shorter bush beans opens up more space between the plants and has been shown to reduce disease prevalence when compared to tomato plants situated closely together. And it doesn’t have to be beans. Any short-statured plant would also separate the plants and improve air circulation.

17. Hairy vetch (Vica villosa):

Another deterrent for Septoria leaf spot and early blight, a cover crop of hairy vetch has been shown to reduce foliar disease in tomatoes more than the use of plastic sheet mulches. And because it’s a legume, hairy vetch also adds nitrogen to the soil. Plant it in the fall and cut the plants down by hand, or with a mower or weed whacker, right when the first seed pods appear on the vetch plants in late spring. Don’t wait until the pods swell. Leave the residue in pace and plant the tomatoes right through it. This also works to deter weeds.

18. Mustard greens (Brassica juncea):

Verticillium wilt is a problem for many tomato growers. Growing mustard greens as a cover crop prior to growing tomatoes reduces the prevalence of this disease, but only if the mustard plants are turned into the soil a few weeks prior to planting the tomatoes.

Tomato Companion Plants to Increase Pollination

Tomatoes are self-fertile (meaning each blossom is capable of pollinating itself), but a vibration is needed to jostle the pollen loose. Wind or an animal bumping into the plant can knock the pollen loose, but bumble bees improve pollination rates even further, possibly giving you better fruit set. Bumble bees (Bombus spp.) are an easily recognizable group of bees that visit a huge variety of vegetable crops. For self-fertile crops like tomatoes (and peppers and eggplants), bumble bees participate in what’s known as buzz pollination. They vibrate their flight muscles and knock the pollen loose. The following tomato companion plants can help boost the number of bumble bees in and around your garden.

19. Sunflowers (Helianthus spp.):

If you’ve ever grown sunflowers you know they are a favorite of bumble bees (and many other bee species, too). Always plant sunflowers in your vegetable garden to ensure a steady nectar source for bumble bees.

20. Beans (Phaseolus vulgaris):

Plants with hooded flowers, including snapdragons, baptisia, monkshood, lupines, and many members of the pea and bean family (including the ones you’re growing in your veggie garden), can only be opened by the heavy bodies of bumble bees. Yes, peas and beans are also self-fertile, but bumble bees enjoy feeding on their nectar. Always grow either pole or bush beans in your garden to help lure in bumble bees to pollinate your tomatoes.

21. Coneflowers (Echinacea spp.):

Because the large, wide blooms of coneflowers make great landing pads for chubby bumble bees, and they are also pretty darn beautiful, plan to include some in and around your vegetable garden to improve pollination of many crops, including tomatoes.

22. Red clover (Trifolium pratense):

Red clover is another favorite nectar source of bumble bees. Use it as a living mulch to enhance pollinator numbers. It’s also been shown to support a diverse array of other beneficial insects, too. And don’t forget about clover’s ability to fix nitrogen. A win-win tomato companion plant for sure.

Our online course Organic Pest Control for the Vegetable Garden, provides even more information about managing pests using companion planting and other natural techniques in a series of videos that total 2 hours and 30 minutes of learning time.

Be the scientist in your own garden

I hope you’ve found a few science-backed tomato companion plants to include in your garden this season. I encourage you to constantly “play scientist” yourself when working with these different plant partnerships. Observe and take notes, and don’t be afraid to be curious and ask questions. This modern approach to companion planting has much to offer home gardeners, but there’s no doubt personal experimentation will also provide valuable insight and a chance to grow the best garden possible.

For more science-based companion planting strategies, check out my book, Plant Partners.

For more on growing healthy tomatoes, please visit the following articles:

• Tomato Growing Secrets
• Grow a Healthy Tomato Garden
• Control Tomato Disease Organically
• What to Do With Tomato Suckers

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Companion plants for 5 popular crops in the garden - AgroXXI