We often get asked how long a poinsettia should last indoors. It's a difficult question to answer, but we often have customers coming back in March with their poinsettias still flowering. Growing all out poinsettias on-site reduces the stress on the plant considerably and increases the life of the plant right from the start.
A number of factors can affect the flowering time of poinsettias. The variety has a quite large effect on flower time. Some start changing colour sooner than others. Finding a poinsettia that hasn't fully changed colour is one way to have it last longer since you know some blooms are yet to come.
The second major factor in poinsettia lifespan is the temperature. Poinsettias hate the cool temperatures. They don't like any drafts at all and even a very short time in the cold will cause the the plant to deteriorate. Keep the poinsettia away from heat registers or ducts and away from drafty windows or doors. And of course, never transport an unwrapped poinsettia, regardless of how warm it is outside!
Poinsettias also like even moisture. If they dry out, they quickly drop leaves so trying to keep a poinsettia evenly moist is your best bet. At the nursery, we lift our poinsettias and judge the amount of water by the weight of the plant. Don't let your poinsettia dry out, and also be sure it doesn't sit in water. If you have a saucer, water the plant thoroughly so the water runs into the sauce, but empty the saucer within 15 minutes of watering so it's not sitting in water.
Drooping leaves are a sign the poinsettia has gotten too cold. Curling and dropping leaves happens when a poinsettia gets too dry. Poinsettias will often survive these conditions, but they will defoliate and not look as nice for the holiday season.
With those few simple rules, you can keep your poinsettias over the holidays quite easily and often into mid-January or even February and beyond.