Companion planting is an agricultural practice where specific plant species are grown near one another to create a mutually beneficial environment. This strategy is valuable for members of the Solanaceae family, such as tomatoes and peppers, which are heavy feeders that demand high nutrient levels and are susceptible to common pests. Pairing these crops with suitable neighbors can improve soil health, enhance fruit quality, and establish natural defenses against biological threats. This technique builds a more resilient and balanced garden ecosystem.
Companion Plants That Enhance Vigor and Flavor
Many companion plants offer advantages that contribute to the productivity and taste profile of tomatoes and peppers. Basil (Ocimum basilicum) is a common example. Growing basil nearby is believed to increase the essential oil content in tomato fruits, enhancing the tomato’s umami and sweetness while balancing its acidity. Basil also thrives alongside tomatoes because they share similar preferences for warmth, sun exposure, and soil moisture.
Borage (Borago officinalis) provides multiple benefits. Its blue flowers are rich in nectar and attract beneficial pollinators, notably bees, which improves the fruit set on tomato and pepper blossoms. The plant’s leaves are thought to enrich the soil with trace minerals, including potassium, which is linked to robust fruit development and improved flavor. Borage can also help deter the destructive tomato hornworm, though its main benefit is through soil and pollination support.
Root vegetables like carrots and radishes can be interplanted between the main crops to improve soil structure. Carrots and radishes have root systems that occupy different soil layers than the deep taproots of tomatoes and peppers, preventing direct competition for nutrients. As the root vegetables are harvested early in the season, they leave behind small channels that help aerate the soil and improve water infiltration for the deeper roots of the nightshades. Radishes offer an additional benefit by acting as a minor trap crop, drawing flea beetles away from young tomato and pepper plants.
Functional Companions: Natural Pest and Disease Deterrents
Pest and disease management is a primary motivation for companion planting, and certain species provide specific defensive functions. The French marigold (Tagetes patula) is planted for its roots, not its flowers. This plant releases alpha-terthienyl into the soil. This biochemical compound acts as a natural nematicide, suppressing and killing root-knot nematodes (Meloidogyne incognita). These microscopic roundworms can severely damage the root systems of tomatoes and peppers.
Alliums, such as garlic, chives, and onions, function as repellents due to their pungent, sulfur-containing volatile compounds. The release of these compounds, including allicin from garlic, can mask the scent of the tomato and pepper plants, deterring insects like aphids and spider mites. These compounds also demonstrate antifungal properties, potentially inhibiting the germination of fungal spores near the base of the plants.
Nasturtiums (Tropaeolum majus) exemplify a defensive strategy known as trap cropping. These plants attract common garden pests, particularly aphids and whiteflies, which find their foliage irresistible. Planting nasturtiums strategically around the perimeter or interspersing them among the main crops draws insects away from the tomato and pepper plants. The trap crop becomes a sacrificial distraction, allowing the gardener to monitor the pest population and remove the infested plant if necessary, preventing a widespread outbreak.
Incompatible Neighbors: Plants to Avoid
While many plants promote healthy growth, some species actively inhibit tomatoes and peppers and should be kept at a distance. Black walnut trees (Juglans nigra) are an example of allelopathy, where a plant releases biochemicals to suppress the growth of competitors. Black walnuts produce juglone, a toxic compound that is detrimental to nightshade plants, causing wilting, stunting, and eventual death.
Fennel also exhibits allelopathic properties, releasing compounds like anethole from its roots that can stunt the growth of nearby tomatoes and peppers. This aromatic herb should be given its own dedicated space in the garden, isolated from most vegetable crops.
Planting other members of the Solanaceae family, such as potatoes and eggplant, near tomatoes and peppers is ill-advised. These related crops share a susceptibility to the same soil-borne diseases, most notably blights, allowing pathogens to spread rapidly. Corn should also be avoided because it is a tall, heavy feeder that competes with tomatoes for sunlight and soil nutrients. Additionally, corn and tomatoes share common destructive pests, such as the cotton bollworm, which can easily migrate between the two crops.