Place near a sunny window. South, east or west are preferable to a north facing window.
Poinsettias are tropical and will appreciate as much direct sunlight as you can provide.
Maintain a temperature of 65°F-75°F during the day. Dropping temperatures to 60°F at night will not hurt the plant. However, cold drafts or allowing leaves to touch a cold window can injure the leaves.
Water the plant whenever the surface feels dry to the touch. Water until it drains out the bottom, but don’t let the plant sit in water.
Lack of humidity during dry season, particularly in winter, is an ongoing houseplant problem.
If your home tends to be dry and your poinsettia is in direct light, you will find yourself watering it frequently, possibly every day.
January through March
Keep watering whenever the surface is dry.
Starting April 1, gradually decrease water, allowing the soil to dry between waterings. Be careful the stem does not begin to shrivel. In a week or two when the plant has acclimated to this drying process, move it to a cool spot like the basement or heated garage. Temperature around 60°F is ideal.
In mid-May, cut the stems back to about 4 inches and replant into a slightly larger container, with new soil. Water it well and place the newly potted plant back into the brightest window you have. Keep the temperature between 65°F-75°F. Continue to water whenever the surface of the soil feels dry. Once new growth appears, begin fertilizing every two weeks following label instructions.
June and July
Move the poinsettia outside keeping it in a partially shaded location and maintain watering and fertilizing routine.
In early July, pinch back each stem by about an inch.
August and September
By mid-August, the stems should have branched and leafed out. Once again, pinch or cut the new stems, leaving 3-4 leaves on each shoot. Bring the plant back indoors to the sunny spot and continue watering and fertilizing.
Poinsettias are short-day plants, meaning their bud set is affected by the length of light. To re-bloom, poinsettias need about 10 weeks with 12 hours or less of sunlight per day. Beginning October 1, keep your plant in complete darkness from 5pm to 8am. Any exposure to light will delay blooming. Move the plant back to the sunny window during the daytime and continue watering and fertilizing.
November and December
Around the last week of November you can stop the darkness treatment and allow the plant to remain in the window. You should see flower buds at this point. Stop fertilizing about December 15. Keep watering and treat your plant the way you did when you first brought it home in bloom.