Companion planting is a gardening strategy where specific species are grown near one another to create a mutually beneficial environment. This practice means certain plant pairings can boost growth, improve health, or increase the yield of neighboring crops. For tomatoes, carefully chosen companions can offer natural protection from pests, enhance nutrient uptake, and contribute to a more robust growing season.
Plants That Repel Garden Pests
Many herbs and flowers serve as a natural defense system for tomatoes by deterring harmful insects through strong scents or chemicals. The aromatic oils in basil, for instance, repel common tomato pests, including whiteflies, aphids, and the destructive tomato hornworm. Planting basil nearby helps mask the appealing scent of the tomato foliage, making it difficult for adult moths to locate host plants for egg-laying.
French marigolds (Tagetes patula) offer a specific form of protection directly in the soil. The roots of certain varieties release alpha-terthienyl, a compound toxic to root-knot nematodes, microscopic worms that damage tomato roots. For maximum effectiveness, marigolds should be planted densely, ideally before the tomatoes are introduced, to significantly reduce the nematode population.
Borage is another valuable companion, particularly noted for deterring the large tomato hornworm. This annual herb is believed to repel the pest, though some evidence suggests it may also work as a trap crop, luring the hornworms to its own leaves instead. The coarse, hairy texture of the leaves and stems may also contribute to a less appealing environment for the pests to maneuver or lay eggs.
Plants That Improve Soil and Nutrient Availability
Some companion plants are beneficial because they directly enhance the growing conditions for tomatoes, rather than focusing on pest control. Certain root vegetables, such as short-rooted carrots, break up and aerate the soil as they grow, which improves drainage and allows tomato roots better access to oxygen and water. This mechanical action helps mitigate soil compaction around the tomato’s deeper root system.
Borage contributes to soil health by acting as a dynamic accumulator. Its leaves contain trace minerals, including potassium and calcium, which are released back into the soil as the plant material decomposes. Similarly, certain low-growing legumes like bush beans host Rhizobium bacteria on their roots, which fix atmospheric nitrogen into a form usable by plants.
Low-growing plants, such as crimson clover or parsley, serve as a living mulch around the tomato base. This ground cover helps suppress competing weeds and keeps the soil cooler and more consistently moist, which is beneficial for the tomato’s shallow feeder roots.
Plants That Attract Beneficial Insects
A separate ecological strategy involves planting species that attract predatory insects, which then manage pest populations naturally. These companions are designed to be a food source or habitat for the pest’s natural enemies. Dill and parsley, when allowed to flower, produce tiny umbel-shaped flower heads that are excellent nectar sources for small beneficial insects.
These flowers attract parasitic wasps, which lay their eggs inside tomato hornworms, and hoverflies, whose larvae are voracious predators of aphids. Sweet alyssum is another low-growing flowering plant that provides a consistent nectar source, successfully drawing in a variety of beneficial insects like lacewings and minute pirate bugs. The presence of these predators establishes a localized biological control system, offering consistent, long-term pest management.
Cosmos and yarrow are taller flowering options that can be planted at the borders of the tomato patch to serve as insectary plants. By providing pollen and nectar, these flowers encourage the predatory insects to remain in the area and patrol the nearby tomato plants for prey. This approach fosters a healthy ecological balance, reducing the need for chemical intervention.
Plants to Never Plant Near Tomatoes
Just as some plants offer support, others can actively inhibit a tomato plant’s growth, making careful placement a necessity. Fennel is a prime example of an antagonistic companion, as it exhibits allelopathy, releasing chemical compounds through its roots that suppress the growth of almost all nearby plants, including tomatoes. It is best grown in isolation, far from the main vegetable garden.
Potatoes and eggplants belong to the same nightshade family (Solanaceae) as tomatoes and should be kept separate because they share susceptibility to the same diseases, most notably early and late blight. Planting them together increases the risk of a disease outbreak quickly spreading between crops, potentially devastating the entire harvest. They also attract many of the same insect pests, such as the Colorado potato beetle.
Members of the Brassica family, including cabbage, broccoli, and cauliflower, are considered heavy feeders that compete aggressively with tomatoes for soil nutrients. Tomatoes require substantial nitrogen, phosphorus, and potassium, and the high demand from brassicas can lead to stunted growth and reduced fruit yield. Additionally, corn is problematic as it is both a heavy feeder and a very tall plant that can cast too much shade over sun-loving tomatoes.