7 Best Companion Plants for Tomatoes (and 3 to Avoid): Top Picks With Prices
Plant these 7 beside your tomatoes this season to reduce aphids, nematodes, and hornworms — with current seed prices from $2.69 per packet.
Most tomato pest problems — hornworms, aphids, whiteflies, root-knot nematodes — can be reduced significantly before you ever reach for a spray bottle. The strategy is companion planting: growing specific plants within a few feet of your tomatoes that confuse pests, attract their natural predators, or sacrifice themselves as decoys.
Much companion planting advice online is recycled folklore with little evidence behind it. This guide focuses on combinations with real research backing from university extension trials, explains exactly why each plant works, and gives you specific variety recommendations with current seed prices. For the broader principles behind pairing vegetables strategically, our vegetable companion planting guide covers the full system. This article focuses entirely on the tomato bed.
Why Companion Planting Works: The 4 Mechanisms
Not every companion plant works the same way. Knowing the mechanism helps you choose the right companion for your specific problem — rather than planting everything and hoping for the best.
Aromatic interference. Strongly scented plants — basil, garlic, chives — release volatile compounds that disrupt how flying insects locate their host plants. Pests navigate partly by scent; competing aromas create interference that makes it harder to lock onto a target. Basil’s key oils are eugenol and linalool, both documented as deterrents for aphids and whiteflies.
Seasonal Garden Calendar
Know exactly what to plant, prune and sow — every month of the year.
Beneficial insect recruitment. Some flowers attract the insects that eat pests. Borage draws in parasitic wasps that lay eggs inside hornworm larvae, killing them from within. French marigolds attract ladybugs that consume aphid colonies. Nasturtiums attract adult hoverflies — whose larvae are ferocious aphid predators.
Allelopathy. French marigolds (Tagetes patula) release a compound called alpha-terthienyl from their roots — directly toxic to root-knot nematodes in the surrounding soil [1][3]. This is one of the most evidence-backed effects in companion planting, confirmed across multiple field and greenhouse trials by university researchers.
Trap cropping. Nasturtiums are so attractive to aphids that they draw pest colonies onto themselves and away from tomatoes. Sunflowers work the same way for stink bugs — but only if planted early enough to be flowering when tomatoes need the protection most [2].
One honest caveat worth stating upfront: much companion planting advice is anecdotal rather than experimentally verified. A University of Illinois Extension review found that while herb companions consistently outperformed bare-soil controls for pest management in trials, the quality of evidence varies considerably by plant and pest [4]. The seven companions below represent the strongest combined evidence.
Top 5 Companion Plants for Tomatoes — Quick Comparison
These five options cover the most common tomato pest problems and offer the best value per seed packet. All prices from Botanical Interests, checked April 2026.
| Product | Best For | Price |
|---|---|---|
| French Marigold ‘Naughty Marietta’ (Botanical Interests) | Root-knot nematodes + whiteflies | $2.69/packet |
| Italian Genovese Basil — Organic Heirloom (Botanical Interests) | Pest confusion + disease early warning | $2.99/packet |
| Nasturtium ‘Jewel Blend’ (Botanical Interests) | Aphid trap crop + hoverfly attractor | $2.69/packet |
| Borage (Botanical Interests) | Hornworm control + pollination boost | $2.69/packet |
| Common Chives (Botanical Interests) | Aphids + spider mites — perennial value | $2.69/packet |
The 7 Best Companion Plants for Tomatoes
1. French Marigold (Tagetes patula) — Best for Nematodes and Whiteflies
If you add one companion plant to your tomato bed this season, make it French marigold. The evidence case is stronger here than for almost any other combination. University of Minnesota Extension confirmed that marigolds reduce thrip populations in both field and greenhouse conditions, and specifically that French marigolds protect tomatoes from whiteflies through the emission of airborne limonene [1]. At root level, alpha-terthienyl — a compound produced in marigold roots — is directly toxic to root-knot nematodes, one of the most damaging soil pests for tomatoes in warm climates [3].
For nematode control specifically, reach for varieties ‘Nemagold’ or ‘Golden Guardian’, which were developed with elevated alpha-terthienyl concentrations [5]. For general companion planting across a mixed bed, ‘Naughty Marietta’ — the classic single-petal yellow-and-maroon French marigold — is widely available and performs well across the full range of companion functions.
Plant marigolds 12 inches apart, interplanted directly within tomato rows rather than confined to the bed edge. The allelopathic root compounds need to be in the soil zone around your tomatoes to suppress nematodes; perimeter planting only protects the perimeter.
2. Basil — Best for Pest Confusion and Disease Early Warning
Basil is the most popular tomato companion and the most misunderstood one. The widely repeated claim that growing basil alongside tomatoes improves tomato flavor was specifically investigated by Joe Masabni, Ph.D., vegetable specialist at Texas A&M AgriLife Extension — he found no evidence that basil affects tomato taste [2]. That myth is worth retiring. The genuine benefits are more practical.
Basil’s aromatic oils create olfactory interference that makes it harder for flying insects to lock onto their tomato target. University of Minnesota Extension research found reduced thrip pressure when basil was intercropped with tomatoes [1], and an Iowa State University study found herbs as companions consistently produced better pest management outcomes than no-companion controls [4].
The underrated benefit is disease early warning. Basil develops powdery mildew before tomatoes when humidity and temperature become favorable [2]. Treat the first white powder on basil leaves as an alarm — the conditions spreading to your tomato crop are already forming. Act on prevention while you still have time.
3. Borage — Best for Hornworm Control and Pollination
Borage (Borago officinalis) is the companion plant most tomato gardeners overlook. Its star-shaped blue flowers are exceptional at attracting Cotesia congregatus — a parasitic wasp that lays its eggs inside tomato hornworm larvae. The wasp larvae consume the hornworm from within, eliminating it without any intervention from you. One established borage plant can maintain a stable foraging population of beneficial wasps across roughly a 10-foot radius of garden bed.
A useful ratio: one borage plant per four tomato plants. That’s enough to sustain beneficial insect recruitment without borage dominating the bed. Place it at corners or intervals rather than interplanted throughout the rows.
One important note: borage self-seeds aggressively. It will return the following season whether you plan for it or not. Plant it where you’re comfortable having it come back permanently.
4. Nasturtium — Best Aphid Trap Crop
Nasturtiums work on a sacrifice principle: aphids prefer them strongly enough to colonize nasturtium foliage while largely ignoring nearby tomatoes. You’re providing a more attractive target to draw the pest away from your crop — a strategy called trap cropping. When aphid colonies appear on nasturtiums, you can remove affected leaves or introduce predatory insects without disturbing your main planting.
The secondary benefit is hoverfly recruitment. Nasturtium flowers are excellent nectar sources for adult hoverflies, whose larvae are highly effective aphid predators. You’re simultaneously baiting aphids and providing habitat for the insects that eat them.
Plant nasturtiums at the bed perimeter rather than throughout the tomato rows. Easy access to monitor and remove infested leaves matters — the ‘Jewel Blend’ sprawling variety works well for this purpose and establishes quickly from direct-sown seed.
5. Chives — Best Low-Maintenance Perennial Companion
Chives offer some of the best return on investment of any tomato companion: plant once, and they return every spring without replanting. As an allium, chives produce organosulfur compounds that repel aphids and spider mites — the same mechanism that makes garlic and onions effective companions. The perennial advantage means your companion planting infrastructure is already in place before you put tomato transplants in the ground each spring.
In USDA zones 3–9, established chive clumps emerge in early spring, well ahead of tomato planting time. Divide clumps every two to three years to keep them productive. One packet of seed started along the tomato bed perimeter can establish a permanent companion border for the life of your garden.
6. Asparagus — The Long-Game Mutual Symbiosis
The asparagus-tomato relationship is one of the few genuinely bidirectional companion pairings in the vegetable garden. Tomatoes produce solanine — a compound toxic to asparagus beetles — providing real pest protection for the asparagus bed [5]. In return, asparagus releases compounds into the surrounding soil that suppress early blight and botrytis, two of the most damaging tomato fungal diseases [5]. Both crops benefit from the other’s presence, and the relationship compounds over time as both plantings mature.
Because asparagus takes two to three years from crowns to produce harvestable spears, this is a long-term bed design decision rather than a quick seasonal fix. If you’re establishing a new asparagus bed, position it adjacent to where you grow tomatoes annually. For soil preparation details that apply to both crops, see our complete tomato plant care guide.
Start with crowns rather than seeds — ‘Jersey Knight’ and ‘Jersey Giant’ are reliable high-yielding varieties, available for approximately $10–$15 per pack of 10 at most nurseries and garden centers.
7. Garlic — The Scent Screen (With One Important Caveat)
Garlic’s sulfurous compounds disrupt the scent-based navigation that hawk moths use to locate host plants for egg-laying. Since tomato hornworm damage begins with moth eggs deposited on tomato foliage, planting garlic at establishment creates a chemical screen at the most critical stage [5]. Plant cloves in early spring alongside tomato transplants; garlic harvested in July leaves the bed clear just as your tomatoes hit peak production.
The caveat: if your garden has a persistent thrips problem, alliums — garlic, chives, and onions — can attract thrips rather than deter them. Thrips transmit Tomato Spotted Wilt Virus (TSWV), which is far more damaging than the pest pressure alliums help prevent [5]. In a thrips-affected garden, build your companion strategy around basil and marigolds instead, and hold off on all alliums until thrips pressure is resolved.
3 Plants to Keep Away From Your Tomatoes
Potatoes — A Disease Highway
Potatoes and tomatoes are both nightshades (family Solanaceae) and share the same pathogens: early blight (Alternaria solani) and late blight (Phytophthora infestans). Growing them together does not cause blight — but it creates a connected, concentrated host population. If blight arrives in your garden, both crops are vulnerable and adjacent, giving the disease a direct pathway between them [3]. Spores travel by wind and through the soil via infected tubers, so physical proximity matters enormously.
Separate potatoes and tomatoes as far as your garden allows. If space forces a compromise anywhere, make this the separation you protect above all others.
Fennel — The Allelopathic Outlier
Fennel is toxic to most of its neighbors. Its roots release chemical compounds that inhibit growth and reduce germination rates in adjacent plants — a documented allelopathic effect that affects tomatoes, most vegetables, and even many herbs. Nearby fennel stunts tomato growth and reduces yield.
Fennel belongs in its own dedicated bed, isolated from vegetables. If you want the significant beneficial insect attraction fennel provides (it’s excellent for hoverflies and parasitic wasps), plant it as an isolated feature on the opposite side of the garden — far enough that its root zone never reaches the vegetable beds.
Helicoverpa zea is a single insect with two common names: the tomato fruitworm when it attacks tomatoes, and the corn earworm when it attacks corn. Growing both host crops together creates a concentrated, overlapping pest population that supports larger infestations than either crop alone would sustain [5]. Late summer is when populations peak and moths move freely between neighboring plants.
Keep corn and tomatoes in separate garden sections with a different crop type between them. The pest pressure reduces substantially with even modest physical separation.
How to Set Up Your Companion Planting Bed
Distance: Texas A&M AgriLife research confirmed that companion plant benefits extend up to 5 feet from tomato plants — companions do not need to be physically touching tomatoes or in the same row [2]. This gives you practical flexibility within existing bed layouts.
Quantity: University of Illinois Extension specifically notes that sparse companion plantings underperform — the quantity of companion plants matters for benefits to materialize [4]. Aim for at least one aromatic companion (basil, chives, or garlic) per two to three tomato plants, and for marigolds, interplant at least one per row section rather than placing a single plant at the bed corner.
Timing: Start marigolds, basil, borage, and nasturtiums indoors 6–8 weeks before your last frost date, or direct-sow them at tomato transplant time. Garlic cloves go in alongside tomato transplants. Sunflowers used as a stink bug trap crop require earlier planting so they’re flowering when tomatoes are at peak vulnerability [2]. Chives from established perennial clumps are already up in spring before tomatoes go in — no timing coordination needed.
Practical layout: Interplant French marigolds and basil directly within tomato rows. Position nasturtiums at bed edges for easy monitoring and leaf removal. Place one borage plant per four tomatoes at corners or intervals. Let chives establish as a permanent perimeter border that returns each year without replanting.
Frequently Asked Questions
Does companion planting replace pesticides?
No — treat it as one layer in an integrated pest management (IPM) strategy, not a replacement. University of Illinois Extension is explicit that no companion combination provides full-season protection, and benefits depend on the companion plants being actively growing [4]. Use companion planting alongside physical barriers, beneficial insect habitat, and regular monitoring rather than instead of them.
When should I plant tomato companions relative to my tomatoes?
Most companions — marigolds, basil, borage, and nasturtiums — go in at or just before tomato transplant time, after your last frost date. Start seeds indoors 6–8 weeks ahead if you want established plants at transplant time, or direct-sow them the same week you transplant tomatoes. Garlic cloves go in at the same time as tomato transplants. Asparagus crowns are established in a dedicated bed years in advance. Perennial chives are already growing in spring if you planted them the previous season.
Sources
- University of Minnesota Extension — Companion Planting in Home Gardens
- Texas A&M AgriLife Today — Improving Tomato Plants Through Companion Planting (2023)
- Virginia Tech Cooperative Extension — Companion Planting in Gardening (SPES-620)
- University of Illinois Extension — Companion Planting: Anecdotal or Tried and Tested?
- Garden Design — Top 10 Tomato Companion Plants (& What Not to Grow With Them)
- Botanical Interests — Naughty Marietta French Marigold Seeds ($2.69): botanicalinterests.com/products/naughty-marietta-french-marigold-seeds
- Botanical Interests — Italian Genovese Basil Seeds, Organic ($2.99): botanicalinterests.com/products/italian-genovese-basil-seeds
- Botanical Interests — Nasturtium Jewel Blend Seeds ($2.69): botanicalinterests.com/products/Jewel-Blend-Nasturtium-Seeds
- Botanical Interests — Borage Seeds ($2.69): botanicalinterests.com/products/borage-seeds
- Botanical Interests — Common Chives Seeds ($2.69): botanicalinterests.com/collections/chives
