Eggplant 101: A production guide

Genetics: There are a large variety of eggplant (Solanum melongia) or aubergine cultivars available. However, for hydroponic production in greenhouses, the most common cultivars are the purple or black Italian types. There are some cultivars developed for field production that are suitable for hydroponic greenhouse production, but there are also several cultivars developed specifically for controlled environments. While not the most commonly grown, specialty eggplants — such as the wide variety of Asian and Indian cultivars — may provide niche opportunities for commercial producers.

Production systems: The most common production systems used for eggplant are those systems used for other vining or high-wire crops, including Dutch buckets or a gutter system with slabs or bags of substrate. The proper substrate to use depends on the system selected. For Dutch buckets, the most suitable substrates are perlite or lightweight expanded clay aggregate (LECA), whereas slabs are most commonly rockwool or coconut coir.

Propagation and young plant production: Greenhouse eggplants are propagated by seed. Regardless of which production system is being used, eggplants are grown as seedlings and young plants prior to transplanting into final production systems. Seeds are initially sown in small propagation cubes (~50 to 200 seedlings per flat). Germinate eggplant seed between 74 and 79° F. Eggplant seedlings are transplanted into 4-inch blocks of rockwool or coconut coir to grow more before transplanting into systems. While propagation cubes for tomato and pepper seedlings are sometimes rotated, wrapping the stem around the roots, this technique should not be used for eggplant seedlings. Both fertilizer concentration and light intensity can increase after transplanting into blocks.

Nutrient solution: The nutrient solution for pepper plants can be divided into two different phases: 1) early; and 2) full production. Once the young plants are transplanted into their final systems, stronger fertilizer solutions (2.0 to 2.5 mS/cm) than those applied when growing seedlings and young plants are used. Additionally, a fertilizer with a higher nitrogen (N) to potassium (K) ratio can be used for seedlings and young plants, switching to a fertilizer with a more balanced N:K ratio when plants start to form fruits.

Temperature: Eggplant in controlled environments are best grown with air temperatures similar to those which are recommended and used for cucumbers. Daytime air temperatures should be maintained between 75 and 80° F, but should not exceed 85 to 90° F. Temperatures during the night should not drop below 65° F.

Light: As a fruiting vine crop, eggplant will benefit from a high daily light integral (DLI). However, it is likely that investing in supplemental lighting, including the capital and operating expenses, to increase the DLI would not be financially justifiable. Use of supplemental lighting during the seedling and young plant stages would be much more economically viable due to the high plant densities.

CO₂: Like other food crops grown in controlled environments, eggplant yield can be improved with the use of supplemental CO2 when ventilation is minimal.

Pollination: Like the other Solanaceous vine crops (tomato and pepper), eggplant are self-compatible. Pollination assistance, by bumblebees or mechanical means, is not required for adequate fruit set, but it improves yield.

Pruning and training: Eggplant can be trained much like pepper plants, with a single plant becoming bifurcated to produce two stems or leaders that are trained using vine twine. Once the two leaders have formed, remove side shoots throughout production to maintain the leader’s dominance. Stem clips should be used to support stems to the vine twine. Do not employ the lean-and-lower training used for tomato, nor the drape or umbrella methods used for cucumber.

Harvesting: Fruits should be harvested prior to becoming fully ripe in order to avoid tough skin and seed from developing. If fruits are allowed to mature, fruit quality may develop a pithy texture and bitter flavor.

Postharvest care: Short-term storage, less than two weeks, is acceptable. Eggplants are sensitive to chilling injury and are best kept at temperatures between 50 and 54° F.

Christopher (ccurrey@iastate.edu) is an associate professor of horticulture in the Department of Horticulture at Iowa State University.