Dec. 15 is only 14 weeks away. With these lovely, warm temperatures that we're enjoying, why think about December? Believe it or not, if you want your poinsettia to bloom in time for Christmas, you have to start forcing it now.
With temperatures at night dropping below 55 degrees, it's time to bring in poinsettias from outside. Wash off the tops and bottoms of the leaves to rid the plant of pests, and place it in a sunny south window. Give it a light application of houseplant fertilizer. A slow-release type works well.
Now comes the forcing part. A poinsettia only blooms when the days are short and the nights are long. If the nights aren't long enough, the plant only produces leaves, but no flowers (bracts).
Since a poinsettia cannot differentiate the source of light, whether it is the sun, a streetlight, a night light, or a lamp, you have to make sure it receives no light from any source from 5 p.m. until 8 a.m. Even short periods of light during this time can prevent flowering. To ensure that the plant is not exposed to any light, cover it completely at 5 p.m. each day, and leave it covered until 8 a.m. A paper bag can work as long as no light gets underneath the edges of the bag. An opaque piece of black cloth or an upside-down trash can also do the trick. Or, place the plant in a dark closet, but remember never to open it 5 p.m. to 8 a.m.
Give the poinsettia this long-night treatment from the end of September until Dec. 15. Depending on the variety, temperature and daytime light intensity, flowers will mature in 60 to 85 days. The long-night routine is not as critical once you see color on the flowers, but for the best flower production, continue covering the plant until the flowers are almost fully developed.
Try to keep the temperatures at night between 55 degrees and 70 degrees. The lower-end temperatures will produce better flowers. The ideal daytime temperature is 70 degrees. Provide bright sunlight during the day, but keep the plant away from warm and cold drafts. Fertilize the plant only when you bring it indoors in September. Do not fertilize it when it is in bloom. Water it when the soil is dry.
In their native country of Mexico, poinsettias are perennial shrubs that can reach 10 feet tall. With proper care and the long-night treatment, you can keep your poinsettias blooming for years of holiday celebrations.
For more information on plant care and gardening, contact me, 887-2252 or firstname.lastname@example.org, or your local University of Nevada Cooperative Extension office. Check out many useful horticulture publications at www.unce.unr.edu. "Ask a Master Gardener" by e-mailing email@example.com.
-- JoAnne Skelly is the Carson City/Storey County Extension Educator for University of Nevada Cooperative Extension.