Companion planting is a gardening technique involving the strategic placement of different plant species near each other to create a mutually beneficial environment. This practice enhances the growth, vigor, and yield of the primary crop by leveraging the natural properties of its neighbors. For home gardeners, selecting the right companions simplifies garden management. When growing tomatoes, certain herbs are well-suited to share space, offering natural protection and flavor enhancement.
Beneficial Herbs for Pest Control
Many herbs possess strong aromatic compounds that confuse or repel insects that commonly target tomato plants. French Marigolds, often treated as herbs in this context, offer powerful protective properties. Planting varieties like Tagetes patula helps control root-knot nematodes, which are microscopic worms that damage tomato roots. The marigold roots release alpha-terthienyl, a substance toxic to these soil-dwelling pests.
Mint is a highly effective deterrent, particularly against aphids, whiteflies, and flea beetles, due to its strong concentration of menthol and pulegone. The powerful scent masks the odor of tomato foliage, making it difficult for pests to locate the host plant. However, mint has an aggressive, spreading root system. It must be planted in a container near the tomatoes rather than directly in the garden bed to prevent competition for water and nutrients.
Other herbs like Rue repel pests such as aphids and whiteflies due to their intensely bitter and pungent nature. The oils from these herbs create a protective barrier around the tomato plant. Thyme, for example, produces essential oils that disrupt the host-finding behavior of the tomato hornworm. These aromatic herbs provide a non-toxic defense, supporting a robust and productive tomato season.
Beneficial Herbs for Soil Health and Flavor
Certain herbs contribute to the tomato plant’s success by improving the surrounding soil or enhancing the fruit’s characteristics. Basil is the most well-known companion herb, with many gardeners believing it enhances the tomato fruit’s flavor profile. While the exact chemical mechanism for flavor improvement is debated, basil may release volatile compounds that prime the tomato’s defense system. This leads to a healthier plant that can focus its energy on fruit production.
Borage, with its blue, star-shaped flowers, is an excellent companion offering environmental and growth benefits. The plant is considered a dynamic accumulator because its deep taproots draw up trace minerals, such as calcium and potassium, from deeper soil layers. When borage leaves decompose, these minerals are released near the soil surface, becoming available to the shallower tomato roots.
Borage also attracts beneficial insects, including honeybees and parasitic wasps, which are crucial for pollination and natural pest control. Parsley is another herb that attracts beneficial predators. Once parsley is allowed to flower, it attracts hoverflies, whose larvae are voracious predators of aphids and other insect pests. This helps maintain a healthy balance in the garden ecosystem.
Placement and Care Strategies
Successful companion planting relies on appropriate placement to maximize benefits while minimizing competition. For flavor-enhancing herbs like Basil, planting them in close proximity—9 to 12 inches away from the tomato stem—is recommended. This close spacing facilitates the exchange of root chemicals and volatile organic compounds. When planting in containers, the tomato should be the central focus, placed in the middle of the pot. Herbs should be positioned around the edge to allow the tomato’s root system maximum room to develop.
Herbs chosen primarily for pest control, such as Marigolds, should be planted as a border around the tomato patch or interplanted between the tomato plants. This creates a continuous ring of defense against pests like nematodes and whiteflies. All companion herbs must share the same basic requirements as tomatoes: full sun and rich, well-draining soil. Ensuring similar watering needs is also important, as consistent moisture is necessary for both plants to thrive without causing root rot.
Herbs to Never Plant Near Tomatoes
Just as some herbs enhance tomato growth, others can actively inhibit it through allelopathy. Fennel is the most prominent example of an herb that should never be planted near tomatoes or most other garden vegetables. Fennel releases allelochemicals from its roots that actively stunt the growth, seed germination, and fruit production of nearby plants.
Fennel’s negative effect is so pronounced that it should be isolated in its own container or planted far away from the main vegetable garden. Furthermore, Fennel attracts aphids, which can easily migrate to susceptible tomato plants, creating a pest problem. Mature Dill plants can also be detrimental, as they compete aggressively with tomatoes for nutrients and water, potentially stunting growth and yield.
The dense, wide-growing habits of certain plants, even if not allelopathic, can cause problems by shading out sun-loving tomato plants and competing for resources. Members of the brassica family, such as cabbage, should be avoided due to their heavy consumption of soil nutrients also needed by tomatoes. Avoiding these detrimental companions ensures the tomato plant has access to the light and resources required for a successful harvest.