Companion planting involves strategically placing different plant species near one another to create a mutually beneficial garden environment. Tomatoes are heavy feeders highly susceptible to pests, so this approach can significantly improve their overall health and yield. Choosing neighboring plants with specific properties helps address common tomato challenges like nutrient depletion, pest infestation, and disease pressure.
Plants That Offer Pest and Disease Protection
Plants with strong aromatic properties disrupt the chemical signals pests use to locate tomato plants. Basil is a classic example; its pungent aroma confuses the adult tomato hornworm moth, preventing egg-laying on the foliage. Basil also attracts parasitic wasps, which are beneficial insects that prey on hornworm larvae, offering biological control.
Marigolds, particularly the French variety, protect tomatoes beneath the soil surface. Their roots release alpha-terthienyl, a compound toxic to root-knot nematodes—microscopic worms that damage tomato roots and hinder nutrient uptake. Planting marigolds densely before the tomato season, or interplanting them, helps suppress these soil-borne pests. Alliums, such as garlic and onions, emit strong sulfur compounds that repel insects like spider mites and aphids by masking the tomato plant’s natural scent.
Borage is a valuable companion focused on attracting beneficial insects rather than repelling pests directly. Its star-shaped blue flowers attract bees and tiny parasitic wasps, which are important pollinators and natural predators. Borage also helps deter tomato hornworms and is thought to release trace amounts of calcium and potassium into the soil, which can mitigate blossom end rot in tomatoes.
Plants That Enhance Soil Health
Tomatoes require a steady and abundant supply of nutrients, especially nitrogen, potassium, and calcium, to fuel vigorous growth and fruit production. Certain companion plants actively contribute to the soil’s chemical composition and physical structure to meet these demands. Bush beans, a type of legume, form a symbiotic relationship with soil bacteria that convert atmospheric nitrogen into a usable form. This nitrogen is mostly released when the bean plant dies and decomposes.
A strategy known as “chop and drop” allows the gardener to use nitrogen-fixing plants, like bush beans or clover, as a green mulch once their growing cycle ends. Chopping the plant and leaving the residue on the soil surface allows the nitrogen stored in the roots and foliage to decompose and become available to neighboring tomato plants. Deep-rooted plants, such as daikon radishes or comfrey, enhance the physical soil environment. Their strong taproots penetrate compacted soil, creating channels that improve aeration, water infiltration, and drainage for the tomato’s root system. When these deep roots decay, they leave behind macropores and draw up minerals from deeper soil layers, making them accessible to the shallower-feeding tomato roots.
Plants That Provide Physical Support or Shade
Beyond chemical interactions, some plants provide physical benefits that help regulate the microclimate around the tomato base. Low-growing, leafy plants like lettuce or spinach can be planted under the tomato canopy to act as a living mulch. This foliage shades the soil, keeping the root zone cooler, suppressing weed growth, and reducing water evaporation.
Taller plants can be strategically placed to offer protection from intense summer heat, which can cause sunscald on ripening tomato fruit. Non-competing, vertical growers like sunflowers or pole beans, positioned on the south or west side of the tomatoes, provide light, dappled shade during the hottest part of the afternoon. This deliberate shading regulates the temperature of the foliage and fruit, preventing heat stress without significantly blocking the tomato’s overall light requirement.
Plants to Never Grow Near Tomatoes
While many plants offer synergistic benefits, some pairings actively hinder tomato growth and must be avoided. The Brassica family (cabbage, broccoli, and cauliflower) are heavy feeders that compete aggressively with tomatoes for essential nutrients and water. Both tomatoes and Brassicas demand large amounts of nitrogen and other minerals, and this competition often results in stunted growth and lower yields.
Fennel is a recognized antagonist because of its allelopathic properties; it releases biochemicals that inhibit the growth of nearby plants, particularly tomatoes. This actively suppresses the tomato’s development and should be kept separate from the garden bed. Other pairings, such as corn and potatoes, are problematic because they share susceptibility to certain pests and diseases, increasing the risk of an outbreak. Corn attracts the corn earworm (the same species as the tomato fruitworm), and potatoes can transmit early or late blight to tomatoes, as both belong to the nightshade family.