Phalaenopsis orchid (the moth orchid; Phalaenopsis spp.) is the most sold indoor's potted plant in the world’s major floriculture markets. In the present study, the effects of night interruption light (NIL) quality and different NPK fertilizers were evaluated on the vegetative growth and flowering of Phalaenopsis orchid ‘Evolution’ in a factorial experiment based on Randomized Complete Block Design (RCBD) with three replications. In the first factor, six-old month plants from the last days of August to October, when the length of flower buds was about 5 cm, were grown under NIL in the controlled chambers of a greenhouse. NI was provided by white (NI-W), red (NI-R) and blue (NI-B) LEDs at the significantly reduced intensity of 15-23 mmol m2 s1 PPF. The NIL qualities employed for 4-h a day throughout the dark period. Control plants received 10 h of light during the day. In the second factor, three water-soluble NPK fertilizers including 19-6-20, 12-12-36 and 20- 20-20 were applied separately throughout the entire vegetative and reproductive stage to plants at the concentration of 1 g L1. According to the results, NI-W and NI-B reduced the leaf area compared to the control, while NI-R had no effect. Flowering was not affected by the NIL quality, and all plants flowered upon employed treatments. Under the NI-B treatment, days to the first flower opening, as well as leaf area, were increased; meanwhile, chl a, b, total chl, carotenoid, and the number of leaves and florets in an inflorescence were decreased. Among NPK fertilizers, the highest leaf area and dry weight were found in 19-6-20 NPK. Flowering yield was practically unaffected by the kind of the NPK fertilizer used. However, NPK fertilizer 12- 12-36, led to an increase of P and K contents and a decrease of Ca content in the leaves of plant during the reproductive stage. These results suggest that both NIL quality and NPK fertilizers had different effects on growth and flowering. NI-R and NI-W had more pronounc
