This is the poinsettia production greenhouse of Kenneth Cranfill. He’s a terrific grower, and his poinsettias are always second to none. However, they pretty much look like a greenhouse full of cabbage plants at this point in September.
Things are about to change, however. Nights are getting longer, which means that poinsettias will begin to turn from vegetative to reproductive growth. These green leaves will gradually give way to brightly colored floral bracts by Thanksgiving.
Kenneth has no ambient light (street lights, motion detectors, security lights, etc.) to contend with, so he does not pull shade fabrics over his poinsettias. Growers in more urban areas, however, must pull black shade cloth late each afternoon and remove it early the next morning. Light destroys the flower-inducing hormones that are produced in poinsettias’ growing tips. (It’s the same process with mums, kalanchoes and Christmas cacti.)
If you’re growing your own poinsettia plant, and if you want it to produce its floral bracts on time for Christmas, you’ll need to give it 14 hours of total and uninterrupted darkness each night. The remaining 10 hours each day must be full sunlight. Put it in a closet overnight every night, or put it in a room where no one will turn on lights. Then, during the daytime, put it back outside when temperatures are warmer than 50 degrees. That process needs to start October 1.