Effects of Temperature On Poinsettia Production

Because of higher fuel prices and low production margins, poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) growers are becoming more interested in growing at cooler temperatures for energy-saving benefits; however, quantitative data on plant growth and development of poinsettia cultivars grown under lower temperatures throughout production is lacking.  The objective of this study was to evaluate forty trial poinsettia cultivars from Syngenta Flowers and Paul Ecke Ranch grown in separate greenhouses at temperatures of 65°F (18-19 °C) during the day and 60°F (15-16 °C) at night for cold production, or 75°F (23-24°C) during the day and 70°F (21-22 °C) at night for warm production.  The experiment was conducted at the Oklahoma State University Research Greenhouses starting in August 2009.  Data was collected on number of cyathiums, number of inflorescences, number of bracts, plant height, plant width, and stem diameter in December 2009.  There was a significant difference (P= 0.05) among the interaction between cultivars and greenhouse temperatures for all measured traits for both production systems.  Cultivar and temperature combinations that optimized each trait were determined.  Poinsettia cultivars with the largest stem diameter in both warm and cold production included ‘39-02B’, ‘7-07’, ‘Classic White’, and ‘Enduring Red’.  Poinsettia cultivar ‘HC-18B’ was the only one in the group for highest number of bracts and number of cyathiums in both warm and cold production.  Only one cultivar, '1266', had the most number of inflorescences, and no cultivars were found with the most height or width in both production systems.