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Released: October 01, 2004

Making Last Year’s Poinsettia Bloom Again

MANHATTAN, Kan. – For plant lovers who hung on to last year’s poinsettias, there are ways to make them flower again this holiday season, according to a Kansas State University horticulturist.

Poinsettias are known as “short-day” plants. That means that flower formation is triggered by long periods of uninterrupted darkness, said Ward Upham, horticulturist with K-State Research and Extension.

Plant lovers can start by placing the plants in the sunniest location available during the day. The plants need the light to draw enough energy for good bract coloration, Upham said.

But the next step is just as critical. Poinsettias also need at least 12 hours of uninterrupted darkness.

“Providing uninterrupted darkness can be a problem, unless there’s a room in which the lights are never turned on,” he said.

If such a room is not available, he suggested that the poinsettia be placed in a dark closet or covered with a cardboard box each night for the needed 12 hours. If using the box, all seams should be taped with duct tape to cut off any light.

“Poinsettias take eight to 11 weeks to flower once the dark treatment has been started,” Upham said.

Normally dark treatment starts in early October. Having six weeks, with 12 hours of uninterrupted darkness is critical, he said. For every night in those weeks that the poinsettia doesn’t get 12 hours of darkness, two days should be added to the bloom time. After the six-week dark treatment, the buds have set and the dark treatment is no longer needed.

Nighttime temperatures also have an effect on poinsettias, Upham said. They tend to like temperatures in the 60- to 65-degree F range at night and at 65 to 75 degrees F during the day.

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K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus, Manhattan.

Story by:
Crystal Rahe
cer5665@ksu.edu
K-State Research& Extension News

Additional Information:
Ward Upham is at 785-532-1438