In order to solve the problems of commercial orchid growers, who need to force Vanda flowering for both blooming on demand and uniformity, an appropriate environment to control flower development is a key factor. However, little research has been conducted on this topic. This research aimed to determine the effects of short day cycles on the flowering of Vanda 'Manuvadee', which usually has high productivity from September to February. Plants were grown under seven hour day lengths for three,

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... x, and nine weeks before being moved to natural day length (approximately 12 hours/day), and then compared with plants cultivated only under a natural day length condition (control). All flowers were grown in an environment of 25 ± 2°C, 70-80% relative humidity. 21-21-21 (N-P 2 O 5 -K 2 O) fertilizer was sprayed weekly at an average of 0.44 g per plant. Results showed that forcing under seven hour day lengths for six and nine weeks could on average delay flowering to 22 and 38 days later than the control treatment, respectively. Forced plants had 100% of first flower opening within 55 days, while the control treatment group gradually opened and took approximately 101 days to anthesis. The nine-week short day treatment provided the most inflorescences, and better longevity was obtained with the six and nine-week short day treatments. Short day cycles decreased TNC concentration in leaves, but did not affect C/N balance at the ninth week; however, P and K concentrations increased.