Most people toss their Poinsettias after Christmas but with the proper care you can keep them until next Christmas, according to the University of Georgia Extension Service. 

Poinsettia's like temperatures in excess of 60 degrees, so keep them inside a warm home and away from heating vents of drafty windows.

The plants which originate from a warm climate thrive in  bright, but indirect sunlight for at least 6
hours per day. Premature leaf drop can occur under improper lighting conditions and fluctuations in
temperature. The soil should be kept moist, but not soggy. It’s best to check the pot daily and water when the soil feels dry to the touch. Use water at room temperature and pour out any runoff water that might collects in the tray underneath the pot. Excessive watering can cause root rot.

If your pot is wrapped with decorative foil remove the foil or poke drainage holes in it. Poinsettias do not need fertilizer while the bracts are still colored. Once the bracts have faded prune the plant back to about 8 inches tall. By May it should have put on new growth. Begin fertilizing now with a well balanced liquid houseplant fertilizer. Feed it every 2 – 3 weeks throughout spring, summer and fall.

When nighttime temperatures remain above 55° F your poinsettia can be
placed outside, but protect it from direct sunlight which can scorch the leaves. If it needs re-potting, transplant it into a pot no more than one or two inches in diameter wider than its original pot. Plant it in a potting mix containing a considerable amount of organic matter such as humus or peat moss. Maintain its compact shape, by occasionally pinching or pruning off new growth where the stems branch. However, do not prune it  after September 1st.

If the plant has survived and thrived through the year as a regular green houseplant it can
be brought back indoors in the fall and made to change colors in time for Christmas. Lighting and temperature are critical for a poinsettia to change its colors. 

Around October 1st poinsettias need to be kept in total darkness for 12 – 14 hours every night. Place them in a room, or closet, or under a box where light can be completely shut out each night. During the day time, poinsettias will need to receive 6 – 8 hours of bright, but indirect sunlight everyday during this period. During the night it needs a constant temperature between 60° and 70° F. Continue watering and fertilizing at the regular summer rate. Follow this procedure carefully, and in 8 – 10 weeks your poinsettia should produce colored bracts in time for next Christmas.