Companion planting is a horticultural strategy involving the close proximity of different plant species to achieve mutually beneficial outcomes in the garden. This practice moves beyond simple monoculture to create a dynamic ecosystem where plants support each other’s growth and defense mechanisms. The primary aim is to increase the overall health and yield of the tomato crop by improving soil conditions and managing pests organically. By carefully selecting companions, gardeners can harness natural plant interactions to enhance nutrient availability, attract beneficial insects, or confuse harmful pests, contributing to a more sustainable and productive growing environment.
Plants That Naturally Repel Pests
Many aromatic herbs and flowers act as proactive defenders for tomato plants by utilizing their strong scents or chemical compounds to deter damaging insects. Planting these species strategically creates a protective barrier that interferes with a pest’s ability to locate its host plant. This natural defense reduces the need for chemical treatments and supports a healthier overall environment.
French Marigolds (Tagetes patula) are particularly noted for their ability to suppress soil-dwelling nematodes, which are microscopic roundworms that attack tomato roots. The roots of certain marigold varieties release sulfur-containing compounds called thiophenes, such as alpha-terthienyl, which are toxic to these pests. This chemical is nematicidal, meaning it directly kills the nematodes or prevents their eggs from hatching.
The strong, distinctive aroma of Basil (Ocimum basilicum) acts as a form of scent camouflage, making it difficult for flying pests to detect the tomato plant’s foliage. This masking effect helps repel insects like the tomato hornworm moth, whiteflies, and thrips, which are common threats to the plant. Furthermore, basil’s shallow root system does not compete aggressively with the deeper roots of the tomato plant for water or nutrients.
Similarly, Allium species, such as Garlic and Onions, contribute to pest control through the emission of pungent, sulfurous compounds. These strong odors mask the tomato’s scent and are known to deter a range of smaller pests, including spider mites. A diluted spray made from garlic can also exhibit fungicidal properties, offering a natural defense against common tomato diseases like late blight.
Companions That Enhance Tomato Growth
Other companion plants offer benefits that focus on ecological support, such as improving soil structure, providing essential minerals, or attracting beneficial predators. These supporting species enhance the growing environment, leading to a more vigorous and productive tomato harvest.
Borage (Borago officinalis), a flowering herb with striking blue flowers, is a valuable companion for its ability to attract beneficial insects, primarily bees, which are essential for pollination and fruit set. The plant’s deep taproot structure is capable of mining minerals, notably calcium and potassium, from deeper soil layers. When borage leaves decompose, these minerals are released near the soil surface, providing a natural source of nutrients that can help tomato plants combat calcium-deficiency disorders like blossom end rot.
Interplanting Carrots or other small, quick-growing root vegetables helps to naturally aerate the soil around the tomato’s main root zone. Their root growth creates tiny channels that improve water penetration and oxygen exchange, contributing to better root health for the more established tomato plant. The foliage of these root crops can also attract predatory insects like parasitic wasps, which seek out and control destructive pests such as the tomato hornworm.
Legumes, including bush beans, are included in tomato plantings because of their unique ability to fix atmospheric nitrogen into the soil. Bacteria residing in the root nodules of legumes convert nitrogen gas into a usable form, which is highly beneficial to heavy feeders like tomatoes. This natural process helps replenish soil nitrogen levels, supporting the vigorous vegetative growth required for a large tomato harvest.
Certain flowering herbs like Dill and Yarrow provide a necessary resource for predatory insects, which control pest populations. Dill’s umbrella-shaped flower heads, when allowed to bloom, attract beneficial species like ladybugs and tiny parasitic wasps that prey on aphids and other soft-bodied pests. Yarrow serves a similar function, drawing in hoverflies and lacewings, which are highly effective natural predators.
Plants Never to Combine With Tomatoes
Not all plant neighbors are helpful, and some species can actively harm tomato growth through chemical interference or aggressive competition for resources. Avoiding these detrimental pairings is important to ensure a successful harvest, as negative interactions can stunt growth or reduce the final yield.
Fennel is a detrimental companion due to its potent allelopathic properties. This plant releases chemical compounds from its roots into the surrounding soil, which actively inhibits the growth and development of many nearby plants, including tomatoes. The fennel’s secretions can significantly stunt the tomato’s size and fruit production.
Aggressive competitors like Corn should also be avoided, as they vie directly with tomatoes for soil nutrients, moisture, and light. Corn is a tall, heavy feeder that casts significant shade, a condition detrimental to tomatoes, which require full sun for optimal fruit development. Furthermore, corn and tomatoes share the corn earworm as a common pest, meaning planting them together can result in a larger, more devastating infestation for both crops.
Plants belonging to the Brassica family, such as Cabbage, Broccoli, and Cauliflower, are poor companions because they are vigorous, heavy feeders with high nutrient demands. When planted next to tomatoes, these plants aggressively deplete the soil of nitrogen and other essential elements, leading to nutrient deficiencies and weakened growth. Similarly, the Black Walnut tree should be kept far from tomatoes, as its roots secrete a toxic substance called juglone, which is lethal to many plants, including all members of the nightshade family.