To prevent your poinsettia from getting too tall, pinch off or prune the growing tips when they are about 4-6 inches long. If the new shoots grow another 5 inches before late August, repeat the process. Pruning shapes the plant to form an attractive compact growth. Beginning Sept. 25, poinsettias need complete darkness from 5 pm to 8 am daily. Lights from any lamps will prevent normal flowering of an uncovered plant.
Poinsettias bloom according to daylength.
Varieties are grouped according to the amount of time between shorticulture days and the appearance of colored bracts. Cultivars such as Amy and Lady will bloom about eight weeks after the onset of shorticulture days. Other cultivars may respond differently. If plants get too tall and you want to propagate them, take leafy cuttings during early to mid-August. Cuttings should be about 4 inches long and may be rooted in any pasteurized media.