Spectrum of low-intensity screw-in horticultural light-emitting diode lamps influences time to flower and finished quality of long-day ornamental species

Abstract

Bedding plants with a long-day (LD) flowering requirement constitute a substantial portion of annuals and perennials produced in the United States for spring sales. However, greenhouse production often occurs when the day length is naturally short and not conducive for flower induction of LD plants (LDPs). Thus, growers must create artificial LDs through day-extension, cyclic, or night-interruption (NI) lighting to promote flowering of LDPs. Many low-intensity, screw-in horticultural light-emitting diode (LED) lamps are now commercially available, though their emission spectra vary. Therefore, the objective of our study was to quantify the influence of various commercially available low-intensity screw-in horticultural LED lamps on the flowering and growth responses of LDPs. We grew several obligate and facultative LD annuals under either a 9-h truncated short-day (SD), or a 9-h SD with NI lighting from 2200 to 0200 hr each day. NI treatments consisted of Feit 9-W Non-Dimmable Plant Grow Lights (Feit), General Electric (GE) 10-W Arize™ Greenhouse Pro-Photoperiodic LED Lamps (GE), Philips 13-W GreenPower LED flowering lamp 2.0 s (Philips), or TotalGrow ™ 16-W Pure Flowering 200 Lamps (TotalGrow). Philips and GE lamps hastened flowering of all LDPs studied, while TotalGrow lamps promoted or hastened flowering on a genus-specific basis. Flowering was delayed by up to 11 d under Feit lamps and plants developed more nodes and inflorescences at open flower than the other lighting treatments. Generally, the height of plants within genera were similar regardless of the lighting treatment. However, plants grown under TotalGrow lamps had a larger stem length than those grown under the other lighting treatments as they emitted the highest percentage of FR light. Therefore, greenhouse growers should not base their decision solely on the price of lamps.