The production value of potted orchids in the United States has increased tremendously in the past decade, and they are now the second-most valuable potted flowering plant. Commercial orchid production has been impeded by the lack of information on flowering requirements of the vast majority of orchid species and hybrids. The objectives of this study were to determine if and how constant and fluctuating day and night temperatures influence flowering of four orchid hybrids. Phalaenopsis Miva Smartissimo x Canberra '450', Phalaenopsis Brother Goldsmith '720', Odontioda George McMahon 'Fortuna', and Odontioda Lovely Penguin 'Emperor' were grown at constant temperatures of 14, 17, 20, 23, 26, or 29°C, and day/night (12 h/12 h) temperatures of 20/14, 23/17, 26/14, 26/20, 29/17, or 29/23°C. After 20 weeks, ≥80% of plants of both Phalaenopsis hybrids had a visible inflorescence when grown at 14, 17, 20, 23, 20/14, or 23/17°C. None of the plants were reproductive when grown at temperatures of 29, 29/17, or 29/23°C. In both Odontioda hybrids, ≥90% of plants initiated an inflorescence that did not abort when grown at 14 or 17°C. Time to flowering data for Odontioda were used to develop a thermal-time model relating temperature with inflorescence development. These results indicate that a day/night fluctuation in temperature is not required for inflorescence initiation in these four orchid hybrids. This research information could be used by commercial orchid growers to improve production efficiency and schedule orchids in flower for specific market dates.
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