Abstract
This study evaluated forty poinsettia cultivars to determine which cultivars perform well under cool
growing temperatures. Poinsettias were grown in separate greenhouses at temperatures of 20°C during
the day and 17°C at night for cold production, or 25°C during the day and 22°C at night for warm
production. Number of lateral shoots leading to inflorescences, number of bracts, canopy diameter, and
stem diameter was determined. A significant (P= 0.03) cultivars by greenhouse temperature interaction
existed for all parameters measured. Cultivars were then separated into classes based on greatest
values for each trait. Poinsettia cultivars with the largest stem diameter in both warm and cold
production systems included ‘39-02B’, ‘7-07’, ‘Classic™ White’, and ‘Enduring™ Red’. Poinsettia
cultivars ‘HC-18B’, ‘Winter Blush’, ‘Cortez™ Burgundy, ‘Winter Rose™ Early Red’, ‘7-07’, ‘Silverstar™
Red’, ‘Topez’™, ‘Classic™ Red’, ‘Enduring™ White’, Novia™ Red’, Advent™ Red’, ‘Silverstar™ Marble’,
and ‘1232’ had high bract numbers in both warm and cold production. Only one cultivar, '1266',
produced a large number of lateral inflorescences in both production systems. Poinsettia cultivars
‘Classic™ White’, ‘Mira™ White’, ‘Novia™ Red’, Early ‘Orion™ Red’, ‘Mars’™ Pink’, and ‘Enduring™
Red’ had larger canopy diameters when grown in cool temperatures than under warmer conditions.
Key words: Greenhouse production, temperature, Euphorbia pulcherrima, plant physiology, plant architecture
