Companion planting is one of gardening’s most appealing ideas. Plant basil beside your tomatoes and pests disappear. Add marigolds and nematodes supposedly flee. Tuck in a few herbs and your tomatoes will somehow taste better.
Some of those claims have been repeated for generations, but not all of them hold up particularly well when researchers put them to the test.
That doesn’t mean companion planting is useless. Far from it. Growing a mixture of vegetables, herbs, and flowers can increase garden diversity, provide nectar and pollen for beneficial insects, make it harder for certain pests to locate crops, use garden space more efficiently, and sometimes reduce pest damage.
The trick is understanding what a companion plant can realistically do.
These seven plants make particularly useful neighbors for tomatoes—not because they possess magical pest-repelling powers, but because there are practical reasons to grow them together.
🌿 1. Basil
Basil is probably the most famous tomato companion, and this is one pairing that has more going for it than tradition alone.
Research summarized by Penn State Extension indicates that basil planted with tomatoes can interfere with the way thrips locate tomato plants. Basil may also reduce egg-laying by adult tomato hornworm moths. University of Minnesota Extension likewise notes studies in which basil intercropping reduced thrip populations in tomatoes.
That doesn’t mean a basil plant creates an invisible force field around your tomatoes. Think of it as one tool within a more diverse garden rather than a replacement for checking plants regularly for pests.
Basil and tomatoes are also practical growing companions because both enjoy warmth, sunshine, and reasonably consistent moisture. You can harvest fresh basil throughout tomato season, making the pairing just as useful in the kitchen as it is in the garden.
Give each plant enough room, though. A tomato should not be surrounded so densely with basil that airflow around its lower foliage disappears.
For a closer look at the science behind this classic pairing, see Planting Basil with Tomatoes: Does Companion Planting Really Work?.
🌼 2. Marigolds
Marigolds deserve a place in vegetable gardens, but perhaps not for all the reasons you’ve heard.
You’ll often see claims that simply planting a marigold beside a tomato will repel almost every imaginable pest. Research doesn’t support such a broad promise.
There is, however, evidence worth paying attention to. University of Minnesota Extension notes that several studies found basil and marigolds effective at reducing thrip populations in tomato plantings. Flowers can also provide resources for beneficial insects that help create a more diverse garden ecosystem.
Research into marigolds and nematodes is more complicated. Certain marigold species and cultivars can suppress particular root-knot nematodes under appropriate growing conditions, but that effect shouldn’t be translated into the claim that one decorative marigold automatically protects every neighboring tomato from every soil pest.
Plant marigolds around the edges of a tomato bed or in gaps where they have enough sunlight.
They add color, bloom over a long season, and help make the vegetable garden a more diverse habitat. Even without exaggerated pest-control claims, that’s plenty of reason to grow them.
🌱 3. Thyme
Low-growing thyme makes an interesting partner for tomatoes because it occupies a very different part of the garden.
A mature tomato grows upward while thyme remains close to the soil, allowing both plants to share space without competing for exactly the same growing niche.
There is also some evidence for a pest-management benefit. Penn State reports that basil and thyme used with tomatoes can interfere with egg-laying by yellow-striped armyworm moths. Flowering thyme can also provide nectar for beneficial insects and pollinators.
That doesn’t mean you need to carpet the entire tomato bed in thyme. Tomatoes need plenty of water during fruit production, while established thyme prefers relatively well-drained conditions and doesn’t appreciate constantly wet soil.
Planting thyme toward the sunnier, drier edge of the bed often makes more sense than placing it directly against a heavily watered tomato stem.
Let some plants flower if attracting beneficial insects is part of your goal.
🌸 4. Sweet Alyssum
Sweet alyssum may not appear on every traditional tomato companion chart, but it deserves more attention.
Its clusters of tiny flowers provide food for beneficial insects including hoverflies, lady beetles, lacewings, and parasitic wasps. Many of those insects are predators or parasitoids of garden pests.
Research in Florida high tunnels found that sweet alyssum growing alongside subsequent tomato crops attracted multiple groups of beneficial insects, including lady beetles, soldier beetles, hoverflies, lacewings, and parasitic wasps. Iowa State Extension also recommends sweet alyssum as a way to provide floral resources for beneficial insects.
Its growth habit makes it especially convenient in small gardens. Sweet alyssum stays relatively low, so it can be planted near the edge of a tomato bed without shading the crop.
In hot climates, it may struggle during the hottest part of summer and perform better in spring or fall. In milder areas, it can flower for a surprisingly long season.
The benefit here isn’t that alyssum directly “repels” tomato pests. It helps create habitat for the insects that eat some of them.
That distinction is an important part of modern companion planting.
🌿 5. Dill
Dill is another companion whose real strength lies in the insects its flowers attract.
Once dill blooms, its broad clusters of tiny flowers become feeding stations for numerous beneficial insects. Plants in the carrot family—including dill, cilantro, fennel, and related species—are particularly useful to small parasitic wasps and flies.
Penn State Extension specifically identifies dill among herbs that can attract beneficial parasitoid wasps associated with control of caterpillar pests, including tomato hornworm and tomato fruitworm.
That doesn’t mean a blooming dill plant guarantees you will never see a hornworm. Instead, it provides resources that can help natural enemies remain in and around your garden.
Dill can grow fairly tall, so don’t place a dense stand where it will block sunlight or airflow from your tomatoes. A few plants along the back or edge of the garden usually work better.
And if your goal is beneficial insects, don’t harvest every plant before it flowers.
Allow at least some dill to bloom.
🌱 6. Cilantro
Cilantro is useful for many of the same reasons as dill, although gardeners don’t always think of it as an insectary plant.
When cilantro bolts and produces its delicate white flowers, those flowers provide accessible nectar and pollen for small beneficial insects.
Penn State recommends cilantro and other members of the carrot family for attracting predators and parasitoids such as lacewings, lady beetles, hoverflies, and parasitic wasps. Increasing this kind of plant diversity can help build a more complex garden food web rather than relying entirely on pest-control products.
Cilantro has another useful characteristic: its preferred season doesn’t completely overlap with peak tomato growth.
Cilantro enjoys cooler weather and tends to bolt as temperatures rise—usually just as tomatoes are beginning to take off. Instead of considering bolting a failure, allow a few cilantro plants to flower among or near the tomatoes.
By midsummer, the tomatoes can occupy more of the space as the cilantro completes its life cycle.
It’s a simple form of succession planting that makes better use of a garden bed.
🥬 7. Lettuce
Lettuce makes this list for a completely different reason.
It doesn’t need to repel an insect to be a good companion.
Tomatoes take time to become large plants. Early in the growing season, considerable open ground may remain between young transplants. Cool-season lettuce can use some of that space before the tomato canopy fills in.
Later, the shade created by taller tomato plants may help protect lettuce from intense sun and delay heat stress for a little longer. Oregon State University Extension specifically suggests using tall crops such as tomatoes to provide shade for lettuce during warmer weather.
This is companion planting in its simplest and often most useful form: fitting plants together according to their size, season, and growing habits.
Harvest the lettuce as tomatoes become larger and need more room for roots, light, and air circulation.
You gain another crop from space that might otherwise have remained bare early in the season, while the tomato eventually gets the bed largely to itself.
🍅 What Companion Planting Can Actually Do for Tomatoes
The old version of companion planting often treats plants as though they have friendships and grudges.
Tomatoes supposedly “love” one plant and “hate” another. Plant the correct combinations and everything thrives; make the wrong pairing and your garden is doomed.
Plant relationships are more complicated than that.
Researchers increasingly describe companion planting in terms of intercropping, plant diversity, habitat creation, trap cropping, and biological pest management. University of Delaware Extension notes that many traditional companion-planting claims are based largely on folklore, while the better-supported benefits of plant diversity often involve providing nectar and pollen to predators and parasitoids that help control pests.
The arrangement matters, too.
Simply owning a basil plant isn’t enough. Plant density, spacing, flowering time, variety, local pest populations, and environmental conditions can all influence whether an interplanting strategy provides a measurable benefit.
That is why two gardeners can try the same combination and get very different results.
🐛 Companion Plants Won’t Replace Pest Monitoring
Even the best companion planting doesn’t mean you can stop looking at your tomatoes.
Check the foliage regularly, including the undersides of leaves. Watch for missing leaves, chewing damage, spots, discoloration, curled growth, eggs, caterpillars, aphids, whiteflies, or anything else that seems unusual.
Finding a tomato hornworm early is much easier than discovering it after half the plant has disappeared.
At the same time, don’t assume every insect needs to be eliminated.
Spiders, lady beetles, lacewings, predatory bugs, hoverfly larvae, and parasitoid wasps are part of the garden’s natural pest-control system. Planting flowers and herbs nearby is partly about making the garden hospitable to these useful predators.
A garden containing insects is not necessarily an unhealthy garden.
Often, it’s exactly the opposite.
🌻 Diversity May Matter More Than the Perfect Pair
One of the most useful ways to rethink companion planting is to stop searching for one perfect plant.
A garden containing tomatoes, basil, thyme, dill, marigolds, alyssum, lettuce, and other flowers and vegetables offers more structural and biological diversity than an uninterrupted row of tomato plants.
That diversity can make it harder for certain pests to find their preferred crop and provide food and shelter for a wider range of beneficial organisms.
Illinois Extension notes that garden-scale intercropping can provide advantages, but simply combining supposedly compatible species isn’t enough. Planting density, timing, proportions, and environmental conditions all influence the outcome.
So instead of asking, “What one plant should I put beside my tomato?” it may be more useful to ask, “How can I make this vegetable garden more diverse without creating excessive competition?”
That opens up many more possibilities.
📏 Don’t Plant Companions Too Close to Tomatoes
More plants aren’t automatically better.
Tomatoes need room for their roots and foliage. Overcrowding can restrict airflow, make harvesting difficult, increase competition for water and nutrients, and create dense foliage that remains wet longer after rain.
Follow the recommended spacing for your tomato variety first.
Then place companion plants in the unused spaces, bed edges, pathways, or nearby containers where they can contribute without smothering the tomatoes.
Low-growing thyme and alyssum can fit near bed edges. Tall dill can go farther back. Basil can grow between well-spaced tomato plants. Lettuce can occupy temporary early-season gaps.
Think in layers rather than packing every square inch.
🚫 What About Plants You’re Supposed to Keep Away From Tomatoes?
Companion-planting charts often include equally dramatic lists of “enemy plants.”
Fennel is frequently accused of inhibiting everything around it. Brassicas supposedly stop tomatoes from growing. Corn and tomatoes are said to hate each other. Potatoes are commonly placed on the forbidden list.
Some combinations may indeed be impractical, but the reasons are often more ordinary than mysterious chemical warfare.
Tomatoes and potatoes belong to the same plant family and can share diseases and pests, so concentrating both crops in the same small area may complicate pest and disease management. Large crops can shade one another. Plants with very different water requirements can be awkward bedmates. Two heavy feeders planted too densely may simply compete.
There is far less evidence for many of the absolute “never plant these together” rules circulated online.
Use growing requirements, spacing, crop rotation, pest history, and common sense before relying on a colorful companion chart.
🌱 Give the Tomatoes What They Need First
No companion plant can compensate for poor tomato-growing conditions.
Tomatoes perform best with plenty of sunlight, fertile well-drained soil, adequate spacing, and consistent access to water.
Keep weeds under control and add mulch to conserve moisture and reduce soil splash. Support indeterminate plants with sturdy cages, stakes, or trellises before they become too large to handle easily.
Water deeply when necessary rather than continually wetting only the surface, and try to avoid dramatic cycles of bone-dry soil followed by saturation.
If you’re still putting your garden together, 10 Tips for Starting a Vegetable Garden covers the basic decisions that matter more than any companion-planting combination.
Healthy tomato plants are better equipped to tolerate the ordinary challenges of summer.
🌼 So, What Should You Plant Around Your Tomatoes?
If you want the simplest answer, start with basil.
It has some of the clearest tomato-specific research behind it, shares similar summer growing conditions, and gives you something delicious to harvest.
Then add flowering plants.
Marigolds, sweet alyssum, thyme, dill, and cilantro can increase diversity and provide nectar or pollen for beneficial insects. Use lettuce early in the season to make productive use of the open space around young tomato plants.
You don’t need all seven.
Choose plants that you actually enjoy growing and that make sense for the space you have.
That may be the best companion-planting rule of all: build a diverse garden in which every plant has a purpose, rather than expecting one supposedly magical pairing to do all the work.
🌿 Companion Planting Works Best Without the Myths
There’s nothing wrong with traditional garden knowledge. Many useful practices began with gardeners noticing patterns long before scientists studied them.
But companion planting becomes much more useful when we separate plausible benefits from exaggerated promises.
Basil isn’t a pesticide. Marigolds don’t create a pest-free bubble. Dill won’t summon an army of beneficial insects on command.
What these plants can do is contribute to a more diverse garden. Some may interfere with particular pests. Some support predators and parasitoids. Some use otherwise empty space. Others simply grow comfortably under similar conditions while giving you another crop to harvest.
That’s a less magical version of companion planting.
It’s also a much more useful one.
🔗 Related Articles
- Planting Basil with Tomatoes: Does Companion Planting Really Work?
- 10 Tips for Starting a Vegetable Garden
- June Gardening Checklist: What to Plant, Prune & Do This Month
- Heirloom Tomatoes: A Guide to Growing and Cooking
📚 Sources & Further Reading
- Penn State Extension — Herbs Make Good Plant Partners and Companions
- University of Minnesota Extension — Companion Planting in Home Gardens
- University of Delaware Cooperative Extension — The New Companion Planting: Adding Diversity to the Garden
- University of Florida IFAS Extension — Push-Pull Technology and Companion Planting
- Iowa State University Extension — Sweet Alyssum to Attract Beneficials
- Penn State Extension — Attracting Beneficial Insects
- Oregon State University Extension — Companion Planting
