Because flower initiation depends upon the length of the dark period, your poinsettia must be kept completely dark from 5 p.m. to 8 a.m. The time to give this treatment is from the end of September until December 15. Once you can see the flowers developing in the growing plants, i. e., when the floral bracts start to show definite color, it is not as important to continue giving the dark period, though it is advisable to continue until the bracts are almost fully expanded. During the day give the poinsettia as much sunlight as possible. Reduce the amount of fertilizer given after bringing the plant indoors.
Growth is slower in the lower light intensity inside the house.
High night temperatures, coupled with low-light intensity, low nutrition, dry soil or improper photoperiod may delay maturity.