Those poinsettias look so perfect when you buy them before the holidays, but it seems as the decorations get packed up and Christmas spirit dwindles, so does your plant.
According to multiple gardening blogs the care you give to poinsettias needs to change with the seasons.
At Christmastime, your poinsettia needs to be in a sunny room, getting at least six hours of bright, indirect sunlight each day. Make sure it's kept between 65 and 70 degrees during the day and slightly cooler at night. Water the plant when the soil is dry to the touch, and allow plant to drain.
Local plant and garden expert Craig Hignight recommends taking off the decorative wrap that often comes with poinsettias. He also notes that poinsettias are averse to drafts: both warm and cold.
During the springtime, in either March or April cut the plant back (recommendations come between four inches and eight inches tall). Water your poinsettia regularly, keeping the soil moist, not soggy. Once each month fertilize the plant with an all-purpose fertilizer. By the end of May it should be growing, leading you to your next step...
In the summer re-pot your plant into a larger container. Once you're certain you can count on nighttime lows that don't stoop under 55 degrees, you can put your poinsettia outside. Continue to water regularly and start fertilizing more often, every two or three weeks. To keep your plant bushy, not tall, prune stems that grow beyond four or five inches, clipping off just the tips. Stop doing this once you near fall.
The fall months are when you need to start reducing the plant's sunlight exposure. Poinsettias need to be in the dark for at least half the day (at least 12 hours) and need strong sunlight for six to eight hours. Craig Hignight recommends putting the plant in a dark room or underneath a box. That extra time in the dark is what causes poinsettias to start budding and producing flowers. Make this your regular practice for about 10 weeks before the holidays. Continue to water and fertilize as you did during the summer.
If you do all of this, your poinsettia should be ready for Christmas once again.