A relatively recent addition to the U.S. holiday houseplant landscape, poinsettias have, in only 70 years, become this country's No. 1 potted flowering plant. Originally from southern Mexico, poinsettias (Euphorbia pulcherrima) were known as the Mexican flame leaf. In the mid-1800s, Col. Joel Roberts Poinsett, an American ambassador to Mexico, brought samples back to his home in North Carolina. The plant's green and red coloration combined with its natural bloom time---late November and December---secured its place in holiday decor history.
Keep plants in the right location. Poinsettias prefer indirect light. Direct light will cause the flowers to fade and drop more quickly. If your ideal display location is in a sunny location, keep your plants in a lower light "holding area" and move them to their display area for short periods of time---as soon as the guests leave, back they go.
Maintain even moisture. Poinsettias prefer evenly moist soil conditions, but do not allow the soil to dry out. When the top inch of the soil becomes dry to the touch, water thoroughly until water escapes the drainage hole. Do not allow the plants to sit in water. Place the pots on a small amount of gravel or simply pour excess water out of the saucer when drainage is complete.
Keep the plant in a draft-free location with even temperature. Poinsettias prefer stable temperatures between 60 and 70 degrees Fahrenheit.
Maintain your poinsettia after the holidays with regular watering and a monthly application of water soluble, 10-10-10 fertilizer. Periodically trim any dead or damaged leaves. Plants can be set outside when all danger of frost is past and night temperatures do not fall below 55 degrees. Bring them indoors before the first frost in the fall.
Encourage your poinsettias to bloom again. In mid-September, move the plants to a location where they will get complete darkness for 12 hours per day. Any light at all---even lamp light---will diminish bloom color, so put the plant in a closet or cover with light-proof fabric. Water regularly during this phase. Continue this program for six weeks. Move the plant to a bright, southern window. New leaf growth will be red.