Researchers find specialty eggplant varieties grow well in high tunnels

Researchers with the New Hampshire Agricultural Experiment Station at the University of New Hampshire (UNH) have found that eggplant varieties developed specifically for growing in greenhouses and high tunnels produced a prolific amount of fruit, offering Granite State growers another option for their summer vegetable production.

“A comprehensive survey of high tunnel producers that we conducted in 2016 indicated that a surprisingly high number of producers were growing eggplant in tunnels. This number increased further in a 2019 survey. While some cultivars are marketed as being suitable for high tunnel production, there have been no comprehensive studies available to guide selection of eggplant cultivars,” experiment station researcher Becky Sideman says.

According to the USDA’s Census of Agriculture, 92 Granite State farms were growing eggplant to sell fresh to consumers in 2017, an increase from 55 farms in 2012.

Sideman and Leah Ford, undergraduate research assistant, evaluated types of eggplant including several parthenocarpic varieties recently developed for greenhouse and tunnel production. The primary goal of the three-year study at the experiment station’s Woodman Horticultural Research Farm is to compare yields of eggplant varieties in high tunnel production conditions. In addition, they are investigating whether pruning would affect yields compared to no pruning and to compare quality of different varieties in post-harvest storage.

In the first year, researchers evaluated seven varieties of eggplants, Angela, Aretussa, Jaylo, Michal, Nadia, Traviata and White Star. They found only slight differences in total marketable yield between varieties, but varieties differed in percentage of marketable fruit.

“We were impressed by the early, prolific, and prolonged fruit production of high tunnel eggplant varieties. Cumulative yields exceeded six pounds per plant in some cases. We suspect that with earlier planting, this could likely be increased,” Sideman says.

Researchers found aphids and spider mites presented challenges to growing eggplants in high tunnels.

“Throughout the season, all varieties showed a good continuity of production, aside from a dip in early September. This may have been at least in part due to a spider mite infestation in August,” Sideman says. “Growers should monitor frequently for these pests and have a plan in place to manage them if they are detected.”

Regarding pruning, researchers found while the typical field strategy of corralling plants without pruning produced acceptable yields, pruning plants from two to four leaders increased yields. They caution that additional research is needed to confirm this result in additional years and/or locations, and more carefully assess the labor and management costs of these pruning systems.

Finally, some varieties were more susceptible to chilling injury, namely Aretussa, White Star and Michal, showing considerable browning under refrigerator conditions. The variety Angela remained firmer and lost less weight than other varieties when stored at warmer temperatures and showed very little browning when chilled.

“Our results clearly illustrate the problems caused by storing eggplant at temperatures that are too cold or too warm. At temperatures that were much warmer than ideal, such as in the packhouse, eggplant fruit lost much more weight and softened much more than if stored at cooler temperatures. At cold refrigerator temperatures, eggplant lost the least weight and remained very firm, but they suffered chilling injury, showing surface pitting and browning,” Sideman says.

Now in its second year, the experiment has expanded to include eight varieties, and portions of the experiment are being repeated by collaborators Olivia Saunders and Heather Bryant, both with UNH Cooperative Extension in Carroll and Grafton Counties, respectively.

According to Sideman, vegetable and berry growers in New Hampshire face several unique challenges, including a humid climate that favors disease and insect pressures, a short growing season and variable weather patterns, high land values and labor costs

Despite these challenges, the opportunities for local vegetable and berry production are vast. The strong relationship between producer and consumer encourages growers to market innovative crops and products that are unique to their farm or to the region, thereby differentiating themselves from other farms and from supermarkets.