To keep them looking good, give poinsettias a sunny, south-facing windowsill or bright filtered light. Don’t press them close to a cold windowpane however, because this can damage the leaves. Keep them at about 68 degrees F during the day, and cooler at night, to prolong the display.
Poinsettias should be watered regularly and kept evenly moist. Never let plants sit in water; always empty their saucers or planters shortly after watering.
With proper poinsettia care after Christmas, you can get a plant to perform again. Water it until mid-spring, then let it dry out and allow the stems to shrivel. Keep it cool. At the end of spring, cut all growth to a couple of inches above the soil and repot it in new soil. Water well and keep it warm, feeding it with houseplant fertilizer when new growth appears. A month later, move the plant outside to a shady location, pinching out the growing tips in midsummer, before returning it indoors. Give it a sunny spot, watering and feeding regularly; then from mid-autumn, keep the plant in total darkness between 5 p.m. and 8 a.m. It will then re-flower and produce colorful bracts.
It’s common for a few poinsettia leaves to turn yellow and drop off when you first bring them home. Don’t be alarmed — the plant is just reacting to its new living conditions.