Poinsettias need bright, but filtered light, away from strong sun and draughts. They need a minimum temperature of 13-15°C (55-59°F).
Be careful when transporting poinsettias from the shop to your home in the winter, as the cold outdoor temperatures can damage the foliage. Always ask if the shop can wrap the plant in paper right around the top of the foliage, or put it in a plastic bag so that it is completely protected.
Sometimes a poinsettia will start wilting once you get it home, and continue to deteriorate, no matter what you do. This could be due to the plant having been stored in cold conditions in the shop before you bought it. Unfortunately there is little you can do about this. Buying plants from reputable suppliers is recommended.
Water poinsettias sparingly as overwatering can damage plants. As a rule of thumb, only water when the surface of the compost has begun to dry out. The flowering life of plants is extended by humidity, so mist plants regularly.
Feed monthly with a low nitrogen, high potassium fertiliser.
If potting up poinsettias, use three parts John Innes No 3 to one part grit.
Getting plants to colour up again next year
Poinsettias are often disappointing in their second year, but this is the best way to try and get a good display from them in their second year.
Prune back the plants hard in April, to about 10cm (4in).
Repot them, growing them in a light, cool place over summer. A temperature of 15-18°C (60-65°F) is ideal.
Flowering and bract colouring is initiated by short winter day-length, occurring naturally in December and January. So from November onwards, plants should be put in a dark room after twelve hours of daylight and protected from artificial light sources.
Plants need a constant temperature of around 18°C (55°F) to colour up well, so make sure they do not get too cold.
Poinsettias can be propagated by softwood cuttings in May, making sure you wear gloves, as the milky sap can be an irritant.
source: Royal Horticultural Society