There’s nothing quite like the taste of a homegrown tomato, warm from the sun and bursting with flavor. For many of us, getting a great tomato harvest feels like the ultimate gardening win. But even if you give them sunshine, water, and love, one hidden mistake can ruin all your efforts.
Some plants, when placed too close, can quietly sabotage your tomatoes—competing for nutrients, inviting pests, or even stunting their growth. I’ve learned the hard way that not every plant makes a good neighbor in the garden.
Knowing which plants to keep at a distance can make all the difference. With a little planning, you can protect your tomatoes and enjoy baskets full of juicy fruit all season long.
1. Potatoes
You might think keeping nightshade family members together makes sense, but potatoes and tomatoes share more than family ties. They’re vulnerable to the same devastating diseases, particularly late blight. I learned this lesson after losing an entire tomato crop that was planted near my potato patch.
Underground competition is another issue. Both plants are heavy feeders with similar nutritional needs, creating a battle for resources that tomatoes typically lose. Their root systems overlap in the soil, fighting for every bit of water and nutrients.
Potato beetles also love to munch on tomato plants once they’ve had their fill of potato leaves. Keep these cousins at opposite ends of your garden for best results.
2. Corn
Tall stalks of corn create perfect hiding spots for tomato hornworms, those large green caterpillars that can strip a tomato plant overnight. Corn also attracts earworms that happily migrate to your tomato fruits once they’re done with corn.
The height factor causes problems too. Corn creates shade that tomatoes hate, as these sun-loving fruits need at least 6-8 hours of direct sunlight daily. My neighbor’s corn rows cast afternoon shadows over my tomatoes one year, and the yield dropped by half.
Both plants are also heavy nitrogen feeders, creating fierce competition in the soil that can leave your tomatoes nutrient-starved and struggling to produce.
3. Fennel
Among the worst neighbors for almost any vegetable, fennel releases compounds that inhibit growth in nearby plants. These allelopathic chemicals essentially act as natural herbicides, stunting tomato development and reducing fruit production significantly.
The feathery herb attracts beneficial insects, which sounds positive until you realize it’s drawing pollinators away from your tomato blossoms. When I planted fennel near my Cherokee Purples, the tomatoes grew oddly twisted and produced fewer fruits than plants in other parts of my garden.
Fennel’s extensive root system also competes aggressively for water and nutrients. Give this Mediterranean herb its own dedicated space far from your precious tomato plants.
4. Walnuts
Black walnut trees are notorious tomato killers due to juglone, a toxic substance they produce. This chemical seeps from all parts of the tree—roots, fallen leaves, and even the nuts. Tomato plants exposed to juglone wilt dramatically and often die within weeks.
The danger zone extends well beyond the tree canopy. Walnut roots can spread 50-60 feet from the trunk, silently poisoning your tomato patch even when the tree seems far away. I once planted tomatoes in what seemed a safe spot, only to watch them mysteriously wither.
Even after removing a walnut tree, the soil remains toxic for years. Raised beds with fresh soil are your only option for growing tomatoes near present or former walnut territory.
5. Brassicas (Cabbage Family)
Broccoli, cabbage, cauliflower and their relatives compete fiercely with tomatoes for calcium in the soil. When tomatoes don’t get enough calcium, they develop blossom end rot—those dark, sunken spots on the bottom of fruits that ruin your harvest.
The cabbage family also attracts cabbage moths and other pests that can easily hop over to your tomato plants. After placing Brussels sprouts next to my Romas one season, I spent weeks battling cabbage worms that had migrated to the tomato foliage.
Heavy feeding brassicas deplete soil nutrients quickly, leaving little for neighboring plants. Keep these greedy vegetables in a separate garden bed from your tomatoes for healthier plants and better harvests.
6. Cucumbers
Growing habits cause the primary conflict between these summer favorites. Cucumber vines spread aggressively along the ground or up trellises, often smothering nearby tomato plants. Last summer, my cucumber vines escaped their trellis and wrapped around a Roma plant, breaking several branches.
Both plants are susceptible to similar fungal diseases that spread easily between them, particularly powdery mildew. Water splashing from cucumbers to tomatoes can transfer pathogens that neither plant can fight off effectively when growing so close together.
Cucumber beetles love to munch on tomato plants too, making pest management more difficult when these crops share space. Keep at least four feet between these popular garden vegetables.
7. Eggplant
Another nightshade family member, eggplant shares too many problems with tomatoes to make a good neighbor. Colorado potato beetles find both plants equally delicious, and infestations spread rapidly between them. When I planted them together, I watched beetles move from eggplant to tomatoes in just days.
Verticillium wilt and early blight affect both plants, creating reservoirs of disease that can devastate your entire nightshade crop. The spores travel on wind, water, and garden tools, making containment nearly impossible when plants grow close together.
Resource competition is also significant, as both plants need similar nutrients at the same growth stages. This timing means they’re fighting for the same resources simultaneously, weakening both crops.
8. Dill (When Mature)
Young dill actually benefits tomatoes by attracting beneficial insects, but everything changes when dill matures. The adult plants release compounds that can stunt tomato growth and reduce fruit production. I’ve noticed my tomatoes struggle whenever mature dill grows nearby.
Timing creates the biggest conflict. When dill begins to flower and set seed, it sends chemical signals that inhibit tomato development. The tall, mature dill plants can also shade tomatoes, reducing the sunlight needed for optimal fruit production.
The solution is crop rotation and careful planning. Plant dill for early-season benefits, but harvest it before it flowers, or keep it in a separate area where it can complete its lifecycle without harming your tomatoes.
9. Peppers
Surprising to many gardeners, peppers compete directly with tomatoes for the same nutrients. Both being heavy feeders from the nightshade family, they quickly deplete the soil when planted together. My pepper and tomato plants always look nitrogen-starved by mid-summer when grown in the same bed.
Disease transmission becomes a major concern with these related plants. Bacterial spot, early blight, and verticillium wilt easily jump between peppers and tomatoes. One infected plant can spread disease throughout your entire nightshade section.
Flea beetles and hornworms happily feast on both crops, multiplying pest problems in your garden. Though it’s tempting to group these summer favorites together, keeping them separated by less-related plants creates a healthier garden ecosystem.
10. Sunflowers
Those cheerful giants release chemicals through their roots that inhibit tomato seed germination and growth. Known as allelopathy, this natural defense mechanism helps sunflowers compete for resources but spells trouble for neighboring tomatoes.
Height creates another problem. Mature sunflowers can reach 6-12 feet tall, casting significant shade over sun-loving tomatoes. The shade not only reduces photosynthesis but also creates humid conditions that promote fungal diseases in tomato plants.
Sunflowers also attract specific types of molds that can spread to tomato plants. Keep these sunny-faced flowers in a separate part of your garden where they won’t interfere with your tomato harvest.
11. Kohlrabi
Few gardeners realize kohlrabi’s strong growth habit makes it a terrible tomato neighbor. Its shallow, spreading root system competes directly with tomato roots in the top layers of soil where most nutrients are concentrated.
Like other brassicas, kohlrabi is a heavy calcium feeder. Without sufficient calcium, tomatoes develop blossom end rot, leaving you with inedible fruits that have black, leathery bottoms. The competition for this vital nutrient is fierce and tomatoes usually lose.
Kohlrabi also attracts cabbage loopers and other pests that don’t normally bother tomatoes but will happily cross over when plants are close together. Keep these aggressive brassicas far from your tomato patch.
12. Strawberries
Fungal diseases create the biggest problem when strawberries and tomatoes share garden space. Both are highly susceptible to verticillium wilt, with strawberries often carrying the fungus without showing severe symptoms. Meanwhile, your tomatoes wilt and die from the same infection.
Strawberry plants spread by runners, quickly invading tomato root zones and competing for nutrients. Their shallow roots take up water and fertilizer meant for your tomatoes. I once planted strawberries as a ground cover under tomatoes, only to watch the tomato plants struggle all season.
Both crops also attract similar pests, particularly slugs and fruit flies that damage ripe fruits. When planted together, these pests have a continuous buffet, making control nearly impossible. Keep berries and tomatoes in separate garden areas.
13. Okra
Gardeners in warm climates often underestimate okra’s impact on nearby tomatoes. These tall, demanding plants grow quickly and cast dense shade that tomatoes can’t tolerate. After planting okra too close to my Brandywines one year, the tomato production dropped dramatically as the okra towers matured.
Root competition creates another significant problem. Okra develops extensive root systems that aggressively seek water and nutrients, often stealing resources from neighboring plants. During dry spells, this competition becomes even more intense, leaving tomatoes stressed and vulnerable.
Both plants are also susceptible to root-knot nematodes, microscopic soil pests that damage roots. When planted together, these nematodes can build up to damaging levels more quickly, affecting both crops.
14. Broccoli
Heavy feeding habits make broccoli a particularly bad tomato neighbor. Like all brassicas, broccoli demands high levels of calcium and other nutrients that tomatoes also need. I’ve watched tomatoes develop nutrient deficiencies right before my eyes when planted too close to broccoli rows.
The timing creates problems too. Fall broccoli gets planted when tomatoes are at peak production, setting up direct competition when tomatoes need resources most. Spring broccoli is still occupying garden space when it’s time to plant tomatoes, complicating crop rotation plans.
Broccoli also releases compounds that can inhibit tomato growth. These allelopathic effects aren’t as strong as with some other plants, but they’re enough to reduce your tomato harvest. Keep these popular vegetables in separate garden beds.
15. Brussels Sprouts
Few vegetables are as hungry as Brussels sprouts, making them terrible companions for equally hungry tomatoes. Their extensive root systems and long growing season mean they’re competing for nutrients for months. My tomatoes planted near Brussels sprouts last year produced smaller fruits with less flavor.
Pest problems multiply when these plants grow together. Brussels sprouts attract cabbage worms, aphids, and other pests that don’t normally target tomatoes but will happily move over when plants are adjacent. The pest population can quickly spiral out of control.
Both crops also prefer different growing conditions. Brussels sprouts thrive in cooler weather, while tomatoes need heat to produce well. This fundamental difference means one crop is always compromised when they share garden space.
16. Pumpkins And Winter Squash
Their aggressive vines quickly overtake garden space, climbing tomato cages and sometimes even pulling plants down. After my butternut squash smothered two tomato plants last summer, I learned to keep significant distance between them.
Both crops are also susceptible to powdery mildew and other fungal diseases that spread rapidly between plants. The large leaves of squash plants create humid microclimates that promote disease development in nearby tomatoes.
Squash vine borers and squash bugs that primarily target pumpkins and winter squash can damage tomato stems when populations build up. These pests rarely seek out tomatoes on their own, but proximity makes crossing over easy.
17. Cauliflower
Competitive feeding habits make cauliflower one of the worst tomato neighbors. These brassicas require massive amounts of nutrients to form their heads, leaving little for nearby plants.
Soil pH preferences also conflict. Cauliflower prefers slightly alkaline conditions, while tomatoes thrive in slightly acidic soil. This fundamental difference means one crop always suffers when they share garden space.
Root competition creates another significant problem. Cauliflower develops shallow, spreading roots that compete directly with tomato roots for water and nutrients in the top layers of soil. This competition weakens tomato plants and reduces their ability to produce healthy fruits.
18. Red Cedar Trees
Cedar apple rust creates havoc when cedar trees grow near tomatoes. This fungal disease requires both cedar and plants in the rose family to complete its lifecycle, but the spores can affect tomatoes too. Living near several cedars, I’ve battled strange spotting on my tomato leaves that appeared after spring rains.
Cedar trees also produce dense shade and have extensive root systems that compete aggressively for water. During drought conditions, these trees can pull moisture from surprising distances, leaving nearby vegetable gardens parched.
Birds roosting in cedar trees create another problem, as they drop seeds and leave droppings that introduce weeds and potential diseases to your tomato patch. If you can’t remove nearby cedars, plant tomatoes in the sunniest spot farthest from the trees.
19. Asparagus
Although it seems harmless, asparagus competes with tomatoes below the surface more than you might expect. Their roots grow deep and wide, remaining active for years and creating long-term competition for space and nutrients.
Timing is another issue. Asparagus is a perennial crop that wakes up early in the spring and stays in the ground year-round, disrupting tomato crop rotation and nutrient replenishment cycles. Tomatoes prefer a bed that’s fully cleared and enriched before planting—conditions asparagus doesn’t allow.
Asparagus beetles, which normally target ferns, have been known to damage tomato foliage as well when populations get out of hand. These overlapping pest issues make the two poor neighbors in any setup.
20. Anise
This licorice-scented herb may smell sweet, but it harbors a secret weapon—allelochemicals that inhibit the growth of nearby plants, including tomatoes. When I experimented with growing anise for its seeds, the tomatoes nearby had spindly stems and pale leaves, unlike their vibrant counterparts across the garden.
Anise’s volatile oils can interfere with the delicate chemical balance tomatoes rely on in the soil. This disruption leads to delayed flowering and reduced fruiting over the course of the season.
Insects drawn to anise, like aphids and some parasitic wasps, can also create unbalanced pest dynamics in a tomato patch. For best results, treat anise like fennel: give it a wide berth and plant it in its own space well away from your vegetables.