Impact of lighting conditions during forcing on flowering time, morphology and postharvest transpiration of Hydrangea macrophylla

In this study, the main objective was to evaluate the impact of lighting conditions and to test effects of continuous lighting and light quality on morphology, number of flowering shoots, flowering time and postharvest transpiration. Hydrangea macrophylla 'Clarissa' was forced in controlled climate chambers. Extending the photoperiod from 16 to 24 h with high pressure sodium lamps (HPS) did not affect forcing time or morphology, but postharvest transpiration was more than 50% higher when the plants were forced at 24 h compared to 16 h lighting. Additional blue light (30% BL, 400-500 nm) in combination with HPS (HPS + BL) did not change the postharvest transpiration compared to HPS but resulted in more compact plants and one week earlier flowering. White light emitting diodes (LEDs) with 20% BL induced more compact plants, compared to HPS, but the flowering was delayed by one week, and postharvest transpiration increased compared to HPS.