When night temperatures become cool, 55?F-60?F, bring the plant indoors toa sunny location. Beginning Sept. 25, poinsettias need complete darkness from 5pm to 8 am daily. Put a cardboard box or other device over the plant to provide the "shorticulture day". Lights from any lamps will prevent normalflowering of an uncovered plant. Continue this "shorticulture day" treatment until the plant bracts show color in late November

But the major thing to remember is that poinsettias require long periods of darkness starting in October in order to achieve their bright displays during the holidays. That means about 15 hours a day, from 5 p.m. to 8 a.m., during which the plant is kept in a dark closet or under a cardboard box, with no light at all, to produce what is called a 'shorticulture day.'