Ask the Master Gardener: Light exposure is major factor for poinsettia rebloom

By: Elaine Applebaum Placer County Master Gardener
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Question: Can I keep a poinsettia and have it rebloom next year? Answer: While it is possible to get a poinsettia to rebloom in time for Christmas, you may decide it is just not worth the trouble. Poinsettias are native to Mexico where they grow 10 feet tall and live for many years. But they are frost tender and will not survive outdoors in our cold winters. Here, they must be kept indoors between October and May when night-time temperatures drop below 55 to 60 degrees. After the holidays, keep your poinsettia as a houseplant in a spot with bright light. Keep the soil evenly moist (not soggy) and fertilize it once a month. Cut the stems back to about 6 inches in March. Replant into a larger pot in June and move it outside. Once outdoors, continue to fertilize monthly, keep moist and provide six- to-eight hours of direct sun. For a compact plant with many blooms, pinch back each stem every six weeks. Bring the pot back to its bright indoor spot in early fall and continue to water and fertilize regularly. Getting blooms before Christmas is the tricky part. In nature, poinsettias bloom mid-winter to early spring. Flowering is brought on photo-periodically; buds set only when plants experience regular dark periods of 12 hours or more. Commercial growers get holiday bloom by controlling night length and temperatures in greenhouses; homeowners must resort to lower-tech methods. Starting on Oct. 1, your plant will need to be kept in total darkness each night from 5 p.m. to 8 a.m. and then brought into bright light every day. Even a brief exposure to light during the dark period can result in delayed, or no flowering. Daytime temperatures should be between 70 and 80 degrees and then drop 10 degrees lower at night. Continue regular watering and fertilizing during this period. Once the bracts have begun to color, usually around Thanksgiving, you can stop the daily regimen of moving the plant from dark to light and back again. You will need to continue to provide at least six-to-eight hours of bright light each day to develop full color. At this point, you should discontinue fertilizing to prolong bloom. Too much work? Buy new poinsettias for the holidays next year, and enjoy the blooms of your old plants in January or February as nature intended.