Caring for a poinsettia is easy. As long as the plant is in bloom, keep it in a well-lighted spot (direct sun is not necessary once it blooms), with evenly moist (not soggy) soil. Feed the poinsettia every two weeks, year-round, with a complete fertilizer such as 10-5-10.
      Dr. Marc Cathey, director of the U.S. National Arboretum, Washington, D.C., and the Paul Ecke Poinsettia Ranch, suggest the following "holiday" schedule for poinsettia care:

  1. On St. Patrick's day, cut back bracts (the large, brightly colored modified leaves that are often mistakenly called flowers).
  2. Re-pot the plant in a larger container on Memorial Day, and put the plant outdoors for the summer.
  3. Cut stems back by six inches on Independence Day.
  4. Move the plant back indoors to a sunny window on Labor Day.
  5. On Columbus Day, start giving the plant 14 hours of darkness daily. It is a photoperiodic plant, setting colorful bracts and blooms (the small yellow berries in the center of the bracts) in response to shorter daylight periods. Cover it with a large cardboard box if you don't have a light-tight closet — it must have absolute darkness.
          Continue the darkness treatment for eight-10 weeks, putting the plant in a window during the day where it will receive four-six hours of direct sun. Water and feed as usual. As soon as the poinsettia comes to bloom, discontinue the closet procedure.

With this care, and a bit of luck, you will have a colorful plant again for Christmas.