2018 ASHS Annual Conference

Long-day plants (LDP) require night interruption to promote flowering when grown out-of-season (i.e., early spring). Accelerating flower development shortens the cropping cycle and thus reduces crop inputs like water and fertilization. There are multiple ways to promote flowering in LDP. Cyclic night interruption, night interruption applied in many short periods rather than one long continuous period, is less studied than other methods but can effectively provide night interruption. Many greenhouses use moving booms to apply irrigation, fertilization, and pesticides. Small lighting fixtures attached to these booms can successfully provide cyclic night interruption, often termed “boom lighting”. We hypothesize that boom lighting from light emitting diodes (LEDs) can promote flowering of Petunia x hybrida as well as traditional methods. A growth chamber with programmable lighting fixtures can accurately mimic moving irrigation booms by gradually increasing and decreasing the provided light intensity. The effects of cyclic night interruption on flowering was tested using night interruption lighting provided at 30, 60, 120, and 240 second intervals between simulated boom passes. Cyclic night interruption applied to seven-week-old petunia seedlings slightly reduced days to first open flower, by up to 3 days. Our highest cyclic night interruption frequencies, boom passes every 30 and 60 seconds, increased total number of visible inflorescences, but also increased plants height and resulted in less compact plants. To account for additional light from night interruption we also calculated days to flower and the number of inflorescences divided by the total light over a 24-hour period (daily light integral + treatment light integral). This showed that increasing cyclic night interruption frequency does not proportionally reduce days to flower but does proportionally increase the number of inflorescences. Further exploration into the lowest light intensity and lowest frequency that promote flowering are required to make boom lighting more commercially viable.