Your poinsettia isn't done yet
IOWA STATE UNIVERSITY EXTENSION
If you bought or were given a poinsettia for the holidays, you may be wondering how long it will last. If given proper care, they should retain their colorful bracts for two or three months. Toss the poinsettia when you grow tired of it or it becomes unattractive.
For those home gardeners who enjoy a challenge, it is possible to get the poinsettia to bloom again next season. Here’s how to do it.
Cut the stems back to 4 to 6 inches above the soil when new sideshoots develop below the bracts or when the bracts fade in March or April. The poinsettia also may be repotted at this time. When new growth appears, place the poinsettia in a sunny window with temperatures of 65 to 75 degrees. Water the plant when the soil surface becomes dry to the touch and fertilize every two weeks with a houseplant fertilizer.
In late May, move the poinsettia outdoors. Harden or acclimate the plant to the outdoors by placing it in a shady, protected area for two to three days, then gradually expose it to longer periods of direct sun. Once hardened, dig a hole in an area that receives four to six hours of sunlight (preferably morning sun and afternoon shade) and set the pot into the ground.
To obtain a compact, bushy plant, pinch or cut off the shoot tips once or twice from late June to mid-August. Continue to water and fertilize the plant outdoors.
The poinsettia should be brought indoors in mid-September. Place the plant in a bright, sunny window. The poinsettia is a short-day plant. Short-day plants grow vegetatively during the long days of summer and produce flowers when days become shorter in the fall.
To get the poinsettia to flower for Christmas, the plant must receive complete darkness from 5 p.m. to 8 a.m. daily from early October until the bracts develop good color, usually early to mid-December. Protect the plant from light by placing it in a closet or by covering with a box. During the remainder of the day, the poinsettia should be in a sunny window.
-- By James Romer, a horticulturist at Iowa State University Extension, Ames