Effects of White or Red Light Irradiation by LED on Growth and Flowering of Cut Carnation (Dianthus caryophyllus)

Abstract

This study aimed to investigate the effects of irradiation from light-emitting diodes (LEDs) on the growth of cut carnations using the standard-type variety ‘Moon Light’ and spray-type variety ‘Cherry Tessino’ in a warm-climate region of Japan. Carnations in this region are cultivated under heated conditions during the winter. The effects of irradiating carnations with white light (peak wavelengths of 450 and 628 nm) or red light (peak wavelengths of 625 nm) using LED-based continuous lighting or 16 h of extended daylight were examined by assessing the number of days from pinching to flowering, the number of flowers harvested, and flower quality. This study spanned from the first pinching in July to the end of cultivation in May. White or red light irradiation using LEDs reduced the number of nodes at flowering, shortened the number of days to reach flowering on lateral branches that undergo flower bud differentiation during the short-day period, and increased the total number of flowers harvested, although the effects varied depending on the variety and time of year. The effect on cut flower quality was also observed at both wavelengths, hardening the stems of cut flowers from the onset of flowering to December. A comparison of the effects of wavelength, showed that white and red light increased the total number of flowers to the same extent. Continuous lighting increased the number of cut flowers beyond the 16 h period. The findings of this study indicate that white light irradiation with two wavelength peaks is as adaptable as red light irradiation for cut flower carnation cultivation in a warm climate cropping system. Incorporating LEDs in actual cultivation requires consideration of night time operations in the facility when choosing a light source.