Effects of Irradiation with Red or Far-red LED Light on Growth and Flowering in Cut Carnation (Dianthus caryophyllus)

We investigated the effects of irradiation from a light-emitting diode (LED) on the growth of cut carnations using the standard-type carnation ‘Moon Light’ and spray-type carnation ‘Cherry Tessino’ in a warm climate region in Japan, where carnations are heated in winter. We examined the effects of irradiating carnations with light from a red or far-red LED all night or for 16 hr of an extended day on the number of days from pinching to flowering, number of flowers harvested, and flower quality, from the first pinching in July to the end of cultivation in June the following year. Irradiation with light from both a red and far-red LED accelerated growth compared with the control treatments. Light from the far-red LED was more effective at this than that from the red LED, and the all-night treatment was more effective than the 16 hr treatment in shortening the number of days from pinching to flowering and increasing the number of flowers harvested. Irradiation with light from the far-red LED also adversely affected the quality of the flowers harvested. For example, it promoted the production of soft flowers and insufficient number of lateral flowers in the spray-type carnation ‘Cherry Tessino’. The results suggest that red LED irradiation can be used to promote flowering in winter/spring-cropped cut carnation cultivation without quality loss.