Patricia M. Arledge, Sharpe, Kenneth W. | 11/13/2015 10:23:41 PM
News Article for October 12, 2015:
If you still have your poinsettias from last year it is time to control their darkness period if you want them to have colored bracts at Christmas.
Poinsettias have a photo period requirement that has to be met if they are going to show color. The requirement, unlike some plants, is based not on the amount of light but the amount of total darkness. Most growers will give poinsettias 13 to 14 hours of total darkness for 40 days and that will initiate the bracts to turn red or the color of that specific variety.
If it were possible to grow poinsettias in an uninhabited area without any sources of light, the normal night length would probably be enough to meet the requirements but artificial lights are a problem. You might think that it is dark where you live but take a look at the outdoor security lights, lights from homes, car lights and even lightning storms can be a problem.
Growers will use greenhouses and cover them with shade cloth to keep light out. They usually start this around October 5th -12th but since you do not need any extra days to market your poinsettias you should be fine if you start now.
Some people have told me that they put their poinsettias in a closet at night but if you do make sure to seal around the frame and bottom of the door to block all light. Any light that interrupts the dark period will delay the onset of color and you have worked so hard to keep that plant alive all year.
The LSU AgCenter and the LSU College of Agriculture