Eggplant, a warm-season crop, is a member of the nightshade family, Solanaceae, alongside tomatoes, peppers, and potatoes. To ensure a successful harvest, it is important to understand the concept of companion planting, which involves strategically placing plants near one another to provide mutual benefits. Conversely, a good harvest also depends on recognizing which plants are incompatible and should be avoided. Planting poor neighbors can lead to resource depletion, increased disease and pest pressure, or physical inhibition, all of which result in stunted growth and low fruit production.
Resource Competitors
Eggplants are heavy feeders requiring consistent nutrients and moisture to develop large fruit. Placing them next to other aggressive feeders leads to direct competition for finite soil resources. This struggle quickly depletes available nitrogen, phosphorus, and potassium, resulting in poor yields.
Avoid large, sprawling plants like squash, pumpkins, and melons, as they are greedy for surface nutrients and water. These cucurbits rapidly extend their root systems and foliage, monopolizing moisture and fertility in the topsoil. Corn is also a powerful resource competitor; its deep, dense root structure aggressively vies for nutrients alongside the eggplant. This competition causes both crops to suffer from insufficient sustenance, leading to smaller, less vigorous plants.
Disease and Pest Magnets
The biggest risk comes from placing eggplant near plants that share common vulnerabilities to pests and diseases. Eggplant shares the Solanaceae family with tomatoes and potatoes, making these relatives the most problematic neighbors. Planting these crops in close proximity creates an easy pathway for shared pathogens and insects to cycle and rapidly spread through the garden.
For instance, the Colorado potato beetle and the tomato hornworm readily attack both eggplant and tomato plants. Nightshades are also susceptible to soil-borne fungal diseases like Verticillium Wilt, which can remain in the soil for years. When one nightshade plant is infected, planting another Solanaceae species nearby increases the pathogen load in the soil, almost guaranteeing a problem for the eggplant. Avoiding this family of plants prevents widespread infections.
Other problematic plants include geraniums, which carry a pathogen that can stunt eggplant growth, and members of the cabbage family. Although not related, plants like broccoli and cabbage attract pests such as aphids and flea beetles that easily migrate to the eggplant. This proximity turns the neighbor into a pest reservoir, making effective control more difficult.
Physical Growth Inhibitors
Eggplants require full sun exposure and good air circulation to thrive and produce fruit. Certain plants can physically inhibit growth by blocking sunlight or by releasing chemical compounds into the soil. This chemical inhibition, known as allelopathy, is a defense mechanism that can stunt the development of sensitive plants.
Fennel is a well-known allelopathic plant that releases substances inhibiting the growth of many vegetables, including eggplant. It is best grown in isolation, as its chemical properties stunt most nearby crops. Similarly, the black walnut tree produces juglone, a chemical highly toxic to most members of the nightshade family. Planting eggplant within the tree’s drip line or root zone results in yellowing, stunted growth, and likely plant death.
Overly tall or aggressively sprawling plants create excessive shade, reducing the eggplant’s ability to photosynthesize effectively. Lack of adequate sunlight directly limits fruit production. Furthermore, a lack of air movement around the leaves encourages the development of fungal diseases. Therefore, careful garden layout is necessary to ensure the eggplant receives the necessary six to eight hours of direct sun without being overshadowed or crowded.