Light and Temperature
Place the newly acquired poinsettia in a bright sunny window but avoid any area where there is a draft or sudden fluctuations in temperature. Do not allow the leaves to touch cold windowpanes. The poinsettia flower bracts last longer when daytime temperatures are from 60 to 70 degrees F. and there is a slight drop in temperature at night. Thus, the plant does best in a cool room.
Water the poinsettia thoroughly when the top layer of soil feels dry to the touch. Discard the excess water accumulated in the saucer. Do not allow the plant to sit in water.
Fertilize the poinsettia regularly with a water soluble houseplant food following the label directions.
In order to have a well shaped bushy plant for the following Christmas, cut the stems back to 6 inches in height sometime between February and March. Be sure to make the cuts just above a node- the point where a leaf is attached to the stem. Place the poinsettia back on a sunny window sill and water and feed as described above.
Are Poinsettias Poisonous?
This myth has been in place as long as Poinsettias have been available. Because of this myth, and the Poinsettias popularity, the plant has been tested numerous times, and is probably the most tested commercially available seasonal plant. An Ohio State University study has shown that no part of the Poinsettia is toxic to humans or pets. So enjoy without fear.
Spring & Summer
Re-pot, Prune, Place Outdoors, and Prune Again
After danger of frost has past (mid-May in this area) it's time to place the poinsettia outdoors. However, before doing so, check to see if the plant has grown too large for its container. Roots growing through the drainage holes, water running through the soil unusually fast, and soil which dries rapidly between waterings indicates that re-potting is necessary. Place the poinsettia in a new container which is one or two inches in diameter larger than the old one. Use a composted potting soil.
Before placing the poinsettia outdoors prune all shoots to approximately 10 inches in height. Again, make the cuts just above a node. The resulting cuttings can be rooted in water and then potted in potting soil.
Place the poinsettia outdoors where it will receive morning sun and partial shade during the afternoon. While the plant is outdoors check daily to see if watering is needed and continue to fertilize regularly.
Cut off the tips of each shoot at least once while the poinsettia is outdoors to promote branching. Check regularly for insect and disease problems.
Bring the plant indoors and provide total darkness from sunset to sunrise
In order to get the poinsettia's flower bracts to turn red by Christmas, the plant must be in total darkness between sunset and sunrise each day, beginning in early September. Obviously, the plant will be subjected to this dark period while outdoors, but should be brought back inside before the first frost (early to mid October) and placed in a room which is completely dark from sunset to sunrise.
Leave the plant in this room until the bracts begin to turn red, around mid December. The temperature in this room should not be above 70 degrees F. If such a room is unavailable, an absolutely light tight box can be placed over the plant each evening and removed early every morning.
Failure to provide this totally dark period each night can prevent the poinsettia from blooming again.