The potential photoperiodic effects and interactions with temperature were identified for flowering of german primrose (Primula obconica). The german primrose `Libre Light Salmon' was grown at long days (LD, 16 hours) or short days (SD, 8 hours) and 61 or 68 °F (16 or 20 °C). Visible bud (VB, 2-mm flower buds) averaged 90 days from seeding for plants grown at 61 °F independent of photoperiod or at 68 °F under LD. At 68 °F and SD, VB was delayed and flowering (horizontal petals) had not been observed at termination of the study (146 days from seeding). Flowering averaged 111 days at LD and 68 °F, 122 days at LD and 61 °F, and 133 days at SD and 61 °F. When plants within each temperature were shifted at weekly intervals from one photoperiod to the other, increasing duration of initial SD resulted in slower VB and at 68 °F more than 8 weeks resulted in no flowering. Changing to SD from initial LD did not affect VB or flowering at either 61 °F or 68°F. These results suggest flowering of german primrose is faster under LD than SD at the recommended production temperatures of 65 to 68 °F (18 to 20 °C).
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