Tomatoes and eggplant can be successfully planted in close proximity within a garden. Their compatibility stems from their shared botanical classification as members of the Solanaceae family, commonly known as nightshades. Both crops thrive under the same environmental conditions, making their cultivation together efficient for the gardener. The primary challenge lies in their shared vulnerabilities, which require careful management to ensure a healthy harvest.
Shared Growing Requirements
The mutual preference for intense sunlight is a major reason these plants are often intercropped. Both tomatoes and eggplants require a minimum of six to eight hours of direct sun daily for vigorous growth and abundant fruit. They are also heat-loving crops, preferring daytime temperatures between 75°F and 85°F to stimulate flowering and fruit set.
Soil conditions also align for both nightshades, as they thrive in fertile, humus-rich, and well-draining soil. An ideal soil pH level for both crops hovers around 6.5, which is slightly acidic. Both plants are considered heavy feeders, requiring a consistent supply of nutrients throughout the growing season, especially nitrogen and phosphorus.
Their watering schedule is nearly identical, requiring consistent moisture to prevent stress, fruit cracking, or blossom end rot. Gardeners should aim to supply about one to two inches of water per week, ensuring the soil remains evenly moist but never waterlogged. This shared need for uniform moisture simplifies the overall care routine when planting them together.
Identifying Common Vulnerabilities
The shared family relationship that makes their cultural needs similar also creates their greatest risk: a shared susceptibility to pests and diseases. If one plant develops a problem, its close relative is highly likely to be affected by the same pathogen or insect. This concentration of vulnerable hosts in a single area allows pest and disease populations to multiply rapidly.
Both crops are attractive to the tomato hornworm (Manduca quinquemaculata) and the tobacco hornworm (Manduca sexta), large caterpillars capable of quickly defoliating plants. Eggplants are a particular favorite host for flea beetles (Epitrix spp.), small insects that chew numerous “shot-hole” perforations into the leaves, which can severely stunt growth.
The most serious shared threats are soil-borne fungal diseases, such as Verticillium Wilt and Fusarium Wilt. These pathogens can persist in the soil for years and target many species within the Solanaceae family. Additionally, diseases like Early Blight (Alternaria solani) can easily jump from a tomato plant to a nearby eggplant, causing concentric brown spots on leaves and premature defoliation.
Strategic Placement for Success
Mitigating the shared vulnerability requires strategic placement and proactive management techniques. Proper spacing is the first line of defense against disease transmission, as it promotes good air circulation and prevents the spread of fungal spores. Tomatoes generally need 24 to 36 inches between plants, while eggplants require 18 to 24 inches, and these minimum distances should be maintained between the two species.
Implementing a strict crop rotation schedule is necessary to prevent the buildup of soil-borne diseases like the wilts. Gardeners should avoid planting any Solanaceae family member, including potatoes or peppers, in the same plot for a minimum of three to four years. This long rotation cycle helps starve out residual pathogens in the soil.
Physical barriers and companion planting can further reduce pest pressure and movement between crops. Placing cages or stakes on both tomatoes and eggplants keeps foliage off the ground, reducing contact with soil-borne pathogens. Companion plants like basil and marigolds can be interspersed; basil repels common pests like whiteflies, while marigolds help suppress soil nematodes.