Temperatures

Growing Temperatures

For best bract development, maintain temperatures of 67 to 68°F nights and 72 to 74°F days. After the middle of October until two weeks before shipping, temperatures can be lowered to 70°F days and 68°F nights. Night temperatures greater than 73°F can cause a delay in bract coloration or even prevent flower initiation. (If the plants need to be pushed, a night temperature of 70°F can be used.) Too low of an average daily temperature will slow plant development, delayed color, reduced bract size, and result in lower leaf loss. The effects of temperatures are discussed under: Temperature Related Disorders.

Cold temperature delay of coloration.
Click on images for larger versions. (images © Brian Whipker, NCSU)

Temperatures should be maintained at 70°F days and 68°F nights until after bracts have formed. Reducing temperatures before bract formation will reduce bract size. After the bracts have formed, temperatures can be dropped to 60 to 62°F. This should be done gradually by decreasing temperatures by 2°F per day. Lower temperatures help improve bract coloration and help prevent premature cyathia abscission. Temperatures should be maintained above 55°F to prevent chilling injury to poinsettias. Temperatures above 75° F after the bracts have formed will cause fading of bract color and a generalized decrease in plant quality. The concept of DIF (difference between the day and night temperature) can also be used to control plant development. DIF is described under Height Control.

Chilling injury to poinsettia bracts.
Click on image for larger version. (image ©Joe Love, NCSU)