General
Say Christmas flower and the Poinsettia is probably the first thing that comes to mind and for good reason. The Poinsettia is the third largest flowering plant sold in the United States with approximately 65 million pots sold in 2006. Poinsettias are grown in all 50 states but California tops the list with about 27 million pots sold in 2006. The Poinsettia is native to southern Mexico through northern South America where it grows to a height of roughly 12 feet tall and is a woody, small tree of the Euphorbia family.
The popularity of the Poinsettia is the brightly colored bloom which is actual modified leaves called "Bracts", with the actual blooms being small yellow bead-like clusters in the center of the bracts. The range of color for Poinsettia's range from red, salmon, pink, yellow, cream, white and bi-colors. Red is still the primary color sold, but new colors and forms are being introduced every year.
Light
Poinsettias prefer bright light, but no direct sunlight while in bloom. During the warmer months Poinsettias will do best if moved outdoors where they will receive a few hours of morning sun but light shade the rest of the day.
Temperature
Poinsettias will tolerate hot temperature outside provided they are given mid day and afternoon shade and ample water. Otherwise, Poinsettias have few demands other than during the resting and blooming periods, which are discussed in detail later. But in general, Poinsettias need to be kept cool during dormancy and a cooler environment during bloom will greatly improve bloom longevity.
Water
The soil should never be allowed to dry out (except during dormancy) and if the leaves start to wilt, it is to late and the plant will start to drop its leaves. Water the plants when the soil is dry on the surface and never allow it to stand in water. In general, the Poinsettia prefers to remain moist, but not wet at all times except during dormancy. Remove the plant from foil wrappers or decorative pots to water the plant and discard standing water in the saucer.
Fertilizer and Feeding
Continue to feed your Poinsettia with an organic slow release fertilizer 
during the growing season according to label directions. Discontinue feeding when dormancy begins. During the blooming period indoors, feed your Poinsettia with a 1/2 strength liquid houseplant fertilizer with every 3rd or 4th watering.
Soil
Poinsettias are not particular about their soil as a general rule. Use a high quality potting mix that drains well and is high in organic matter. Avoid potting mixes with added fertilizer, as these tend to have to much fertilizer, especially nitrogen that will interfere with blooming.
I'm not a big fan of "polymer moisture crystals", especially for house plants in the winter. I have suspicions that they may keep most plants to wet in the winter time and especially when you are already trying to hold back water a little. If you choose to use these products, do so with caution and bear in mind that if the roots start to rot or the bract coloring starts to be effected because of them, it is possibly to late to correct the problem.
Potting
The standard rules of potting apply to Poinsettias. When you need to repot, move up only one pot size at a time. The exception being that if you root your own cuttings, you plant into a 3 inch pot to get it established and then you should pot up to the finish pot size, usually 6 or 8 inch diameter. After which, repot as normal.
Blooming
The Poinsettia is a plant that has become a staple in many homes, churches and businesses at Christmas each year and is relatively easy to grow and it will rebloom as long as certain strict requirements are met. Keep your Poinsettia away from drafts, heat registers and quick or extreme temperature fluctuations. Keep the plant in a temperature of around 72 degrees F during the day and 60 degrees F at night.
To get your Poinsettia to rebloom, it requires short days (9 hours) and long nights (13 hours) in order for the bracts to start turning color. This process is not difficult, but it is extremely demanding in its discipline and do not attempt this process if you do not have the time or ability to stick to it. Choose times that will work for you to cover and uncover the plant each day, say 6 P.M. and 7 A.M. Starting around the middle or later part of September at the time you chose move the plant into total darkness or cover the plant with a light-proof covering. Each morning at the time you chose, uncover the plant and place it back in bright light. When the leaves start turning color, discontinue the dark periods as the cycle has now started and keep the plant in a warm location in bright light as described above.
When you start the process of dark periods, you must not allow any interruptions either in days or during the period of darkness. Any interruptions will normally interrupt the cycle and you will need to start over. But this just means your plant will flower later than you wished (Poinsettias normally bloom in January and February in the wild). The discipline of providing dark periods without interruptions or exceptions for a period of 2 to 2 1/2 months is the part of the process that causes many to give up on Poinsettias and for some writers to recommend not attempting it. But if you have the determination and willingness to adhere to this strict discipline for a short time, you will be richly rewarded with beautiful color each Christmas that was created (coaxed) by you.
Dormancy
