If you must try, remember that poinsettias are considered “short day” plants, meaning that they need a short light period for several weeks before they will bloom. This will require your constant attention and will require that you place the plants in total darkness every night from about 6 p.m. to 8 a.m. the next day. This procedure must continue for 10 weeks or so, or until the plants start to “rebloom” or develop color.
After Christmas, grow the poinsettia as a houseplant. Keep it evenly moist and in fairly bright light. In late February or early March cut back each of the old flowering stems to 4 to 6 inches in height to promote new growth.
In May repot into a slightly larger pot. Water well and place in a sunny window. When all danger of frost has passed and night temperatures are above 60 degrees, place your poinsettia outdoors in a semi-shady location. Sink the pot in a protected outdoor flowerbed. Some morning sun is OK.
Periodically turn the poinsettia pot to prevent rooting through the bottom hole and to keep the shape uniform. To have a short plant with many flowers, pinch out the top one-fourth inch of the growing shoots to encourage branching. Do this in three- to four-week intervals, according to the rate of growth.
Two or three large fully expanded leaves should be left below the pinch. Continue this practice until mid August, when the plant should have a satisfactory shape and number of shoots.
Keep the plant growing actively all summer by regular watering and fertilizing. Use a complete soluble houseplant fertilizer according to label directions.
Before temperatures fall below 55-60 degrees at night, lift the pot and drench the leaves and soil with water to help remove any pests. Bring the poinsettia indoors to a sunny location and keep it moist, but reduce fertilization.
With poinsettias, as well as Christmas cactus and kalanchoe, flowering is “photoperiodically” induced. This means that flowers begin to form when the days are a certain length, or, more accurately, when the nights are long enough. The poinsettia is a short-day or long-night plant. Without long nights, poinsettias will continue to produce leaves but will not flower.
Very short periods of lighting at night may be enough to prevent or interfere with flowering. Even light from a streetlight can stop flowering. If the plant is to be grown in a room that is lighted nightly, cover it completely at dusk — 5 p.m. — every day with a heavy paper bag, a piece of opaque black cloth, other light-tight cover or place in a dark closet. However they must receive light during the day.
Flower initiation begins in late September and early October. Dark periods longer than 12 hours are necessary for flower set.
Because flower initiation depends upon the length of the dark period, your poinsettia must be kept completely dark from 6 p.m. to 8 a.m. In order to get them in flower at Christmas, this treatment should start at the end of September and run until Dec. 15.
Once you can see the flowers developing and the bracts show color, it is not as important to continue giving the dark period, though it is advisable to continue until the bracts are almost fully expanded.
Temperatures should be no less than 55 degrees at night, but not more than 70 degrees. High night temperatures, coupled with low-light intensity, low nutrition, dry soil or improper photoperiod may delay flowering.
If all this seems like a lot of work, then it may be best to leave growing poinsettias to the professionals.
Randy Drinkard is a technical writer for The University of Georgia Center for Urban Agriculture and ANR Agent for Troup/Meriwether Cooperative Extension. The Troup County Extension office is located at 114 Church St. in LaGrange, and may be reached at 706-883-1675, Monday through Friday, 8 a.m. to 5 p.m.