Effect of night interruption with colorful LED lamps and fertilizer treatments on growth and flowering characteristics of Phalaenopsis orchid

Phalaenopsis (the moth orchid; Phalaenopsis spp.) is currently the most sold indoor potted crop in the world’s major floriculture markets. The effects of light quality in night interruption (NI) and NPK fertilizers were examined on the vegetative growth and flowering of Phalaenopsis, an Evolution cultivar, in a factorial experiment as a completely randomized design. Young 6-old months plants from the last days of August to October when the length of flower buds was about 5 cm, were grown under ambient light/dark of greenhouse (control), ambient light plus night interruption (23:00–03:00 h) with light intensity at 20 µmol m−2 s−1 with three spectra light including white (400-700 nm), blue (450 nm) and red (680 nm) LED lights. Also, three water-soluble NPK fertilizers including 19N-6P-20k, 12N-12P-36K and 20N-20P-20K were applied to plants at concentrations of 1/1000. The tallest plants (25 cm) at flowering were in the control group in the 20N-20P-20K fertilizer treatment. NI with white LED + 19N-6P-20k or control + 20N-20P-20K effectively increased floret number. To obtain early flowering using 12N-12P-36K (without NI) and NI treatment with white light + 20N-20P-20K and blue light + 12N-12P-36K during their reproductive stage could be suggested. Plants fertigated with 12N-12P-36K and NI with red LED, showed the highest amount of chlorophyll a (0.36 mg/FW) and b (0.17 mg/FW). The highest amount of K and P in all three light treatments were obtained in 12N-12P-36K fertilizer. The experimental results suggested that NI treatment can be used effectively to promote flower induction with an increased growth rate. To obtain high-quality plants, however, NI with red and white LEDs should be considered.