Improving Lettuce Production in Deep Water Culture in the Southeastern United States

Abstract

Greenhouse lettuce production is a small, but growing industry in the Southeastern United States. High variability in the weather makes growing greenhouse lettuce in the southeast difficult. Growers need improved cultural practices to make the greenhouse lettuce industry more profitable. A series of experiments was conducted to determine the best cultivar recommendations and to improve cultural practices. In the first experiment twenty cultivars were trialed for heat tolerance. Nine were selected for a sensory evaluation based on median tipburn and bolting ratings at or below 1 and 2.5, respectively and were rated for crispness, bitterness, overall texture, overall flavor, and marketability. ‘Skyphos’ and ‘Adriana’ had the lowest marketability ratings. We recommend seven cultivars (‘Salvius’, ‘Rex’, ‘Aerostar’, ‘Sparx’, ‘Monte Carlo’, ‘Nevada’, and ‘Parris Island’) as heat tolerant, marketable lettuce in the southeast. Reducing energy costs is a way growers can cut down on the cost of growing greenhouse lettuce. In the second experiment, nutrient solution was heated in a Deep Water Culture system to determine effects of root zone temperature change on lettuce. Nutrient solutions were either unheated (control), continuously heated to a target temperature of 16 °C, or continuously heated to a target temperature of 22 °C using aquarium heaters. Head fresh weight was highest when nutrient solution was heated to 22 °C, but was not significantly different between 16 °C and unheated control treatments. Size index, root dry weight, and head fresh weight all increased linearly with root zone temperature. Heating greenhouse lettuce nutrient solutions during production may decrease energy costs and production times, thereby improving potential profits.