Importance of Calibrating Cultural Greenhouse Growth Practices Using LED Technology in Tomato Production

Production results achieved between two commercial tomato producers in North Carolina highlighted the importance of cultural practices when adding LED lighting. Growers added LED lighting to their greenhouses winter 2014. They were 10 miles apart geographically with identical weather patterns. The growers differed in growing methods, and tomato variety.  To date production yield is significantly different. Grower A used hydroponic-cococoir, growing Heritage tomatoes in a 7,400 square-foot greenhouse housing 2,100 plants. The greenhouse was divided into three bays:  non-lit bay; guard bay; and a bay with 42 LED lights (1 light/59 square feet), photoperiod 15 h. Plants were planted October 2014 and germinated under sole source LEDs. At 8 weeks seedings were transplanted to the greenhouse. Plants under LED lights initially showed signs of phosphorus stress as indicated by anthocyanin in the leaves. We speculated that this stress was because the lights illuminated prior to dawn while the plants were cold from the night. Increasing temperature in the greenhouse 2 degrees centigrade eliminated stress. Water stress was introduced by manipulating fertigation at night to be delivered at 2-minute intervals. The first harvest of the LED-lit crop occurred in February, two weeks prior to the non-lit control. At the time of this submission yield under the LED lights provided a 32% increase over the non-lit control. Grower B used soil-based media in 5-gal pots growing Trust tomatoes in two side-by-side 1,300 square-foot greenhouses. One greenhouse served at the non-lit control and one was illuminated with 12 LED lights (1 light/109 square feet), photoperiod 15 hours. Plants were planted Nov. 2014 under the two growth conditions.  As plants have matured the non-lit control has several indicators of stress, including ethylene and nitrogen, as measured by height and apparent vigor. LED-grown plants were taller and with greater biomass. The first harvest occurred in March. At the time of this submission yield in the non-lit lights greenhouse demonstrate 40% more productivity over the LED greenhouse. Given the vigor of the LED plants they may eventually outperform the non-lit plants. This data will be available at the time of our presentation. Data from similar farms highlights the complexity of adding a new growth parameter. Careful consideration must be made when introducing LED lighting, or transitioning from other lighting.  Growth strategies need to be reconsidered and managed properly, particularly with regard to heating and fertigation.