If you haven't done so already, now is the time to place your poinsettia (Euphorbia pulcherrima) plants in total darkness for 12 to 14 hours a night in order to force blooming. A dark closet or an unused room with no light leaks works well.
Any source of light during the night may prevent your poinsettia from blooming. That applies to light cast from outside sources, like street lights, or stray light from under a door — even the light from a nightlight may be enough to cause an issue with blooming.
Move your poinsettia plant to bright light during the day and return it to darkness at night until the bracts (modified leaves) begin to turn color. This will take several weeks, but should occur in early December. Once they begin to show color you can safely move your poinsettia to the desired location. Bright color will continue to develop.
I just started putting my poinsettia in darkness last night. I have had moderate success in the past because it was difficult to keep it in total darkness in my old home. I tried putting a heavy, black trash bag over it at night, but that didn't really work for me as light always found a way inside. This year my poinsettia will go into a closet with absolutely no light and will not be disturbed until morning.
NOTE: Contrary to popular belief, poinsettias are not a danger to small children and pets. Although the sap can cause minor skin irritations and may cause stomach upset if ingested the National Capital Poison Center explains that poinsettias are safe around children and pets, but suggests keeping them out of reach to avoid accidental ingestion and risking upset tummies.
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