The crops of iceberg and other types of lettuce in water culture are growing well in the plastic (cabrio) greenhouse at Wageningen UR Greenhouse Horticulture in Bleiswijk. The lettuce is growing on the Dry Hydroponics system in two plastic greenhouses. In winter supplemental LED lighting is used during daytime. During hot weather conditions, the greenhouse roof and the side walls can fully open. In this project, year round durable cultivation of high quality iceberg lettuce is being tested. Certain customers, such as the processing industry, require an increasing year-round supply of a product with a constant high quality, which also includes food safety and a good shelf life.
Because of an increase in density from 20.8 to 25 plants/m2 (+ 20%), the head weight of various types decreased by 10%, but the total number of kilos increased by 8%. Compete Plus is added to some ponds monthly. In February, March and April this gave an extra net weight of 15, 5 and 0%, respectively. The effect decreased towards the summer. More growth light in combination with a higher greenhouse and water temperature resulted in the winter in faster growth. The water is heated to 15 or 17 degrees, depending on the light intensity of the artificial light (a higher temperature with more light).