At Christmas time, poinsettias put on a brilliant display of red floral leaves called bracts. However, this phenomenon is only one phase of the interesting life history of this perennial treasure from the tropics.
A Tropical Bush
The poinsettia is a tropical plant that grows and blooms year after year. Eventually it becomes a bush five to 10 feet high.
Poinsettias grow from seeds, cuttings or shoots. A shoot planted in spring will grow to vegetative maturity by the onset of autumn.
A Short-Day Plant
Some plants called short-day plants will bloom only when their leaves are subjected to darkness for a sufficiently long period of time each night. The required period varies with the species. The poinsettia is a short-day plant. In nature the poinsettia will flower in tropical areas where the winter nights do not exceed 13 hours in length. However, to ensure timely flowering in artificial conditions in the United States, it is recommended that plants be subjected to 14 or 15 hours of complete darkness for eight to 10 weeks in autumn.
The showy red flowers of the poinsettia are actually a whorl of bracts called a cyathium (from the Greek word "kyathos," meaning cup). At the center of this red cup the true flowers rest.
The poinsettia flowers continue to bloom until the end of January or even longer. Then the showy bracts and leaves fall off and the plant becomes dormant.
About the beginning of May, the plant begins to grow again. If subjected to sufficient darkness in October and November, it will bloom again in December.