Potted mature Phalaenopsis `Joseph Hampton' orchid (clone Diane) plants were placed in each of four growth chambers with 0, 8, 60, or 160 μmol·m–2·s–1 photosynthetic photon flux (PPF) for 12 hours daily and at 20C day/15C night air. Plants under 160 or 60 μmol·m–2·s–1 PPF began spiking (an elongating reproductive bud protruding through the base of its subtending leaf) in an average of 28 or 34 days, respectively. None of the plants placed under 0 or 8 μmol·m–2·s–1 PPF started spiking within 6 weeks. These plants, following return to a greenhouse, spiked and flowered 8 weeks later than those receiving 160 μmol·m–2·s–1. In a second experiment, plants were placed in each of three growth chambers and kept in complete darkness at 20C day/15C night for 2, 4, or 6 weeks before exposure to 160 μmol·m–2·s–1 PPF. Air was maintained at 20C day/15C night for an additional 6 weeks and then raised to 25C day/20C night to accelerate flowering. Plants exposed to 2, 4, or 6 weeks of darkness required 45, 60, or 77 days, respectively, to reach spiking. However, all plants spiked at similar times (31 to 35 days) after lighting began. Anthesis occurred at progressively later dates for plants placed in darkness for increasing durations, but plants in all treatments required 123 days to reach anthesis following their exposure to light. Flower count and size were not affected in both experiments.
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