Q. Many folks say they save their poinsettias and get them to re-bloom the following year. How is this done?
A. What we often think of as the "flowers" of poinsettia are actually leaves that are called "bracts." The bracts surround the yellow flowers in the center of the pigmented leaves. Once all the pollen is shed from the yellow flowers, the plant begins to drop its leaves. At this point you can begin the process to rebloom Poinsettias from year-to-year by following the steps below.
Start the process after the holidays and plan on keeping the plant healthy during the spring and summer.
• Allow the plant to dry out when about half the leaves have fallen. The plant will go dormant at this point. Keep it in a cool, dark, dry location and water only enough to keep the stems and roots from drying out.
• In early to mid spring, cut the plant back 4 to 6 inches from the soil. You may repot the plant at this point to encourage new growth. Place it in a sunny window and water when the soil is dry as you do other houseplants. You can fertilize occasionally with a diluted liquid fertilizer.
• You can move the plant outside when all danger of frost has passed and night temperatures are 60 degrees. Locate the plant in a garden that gets full sun at least six hours early in the day with shade in the afternoon, and plant it into a hole big enough to include the pot. Turn the pot periodically to allow even growth, and keep the roots from growing outside the pot. Pinch off new shoots to help the plant stay compact. Water regularly and fertilize every couple of weeks.
In Autumn the plant is ready to begin the process of photoperiodism, which is the physiological response poinsettia's have -- leaves changing color -- to the variation in light as nights grow longer.
• Bring the plant indoors when the night temperatures are moving toward 55 to 60 degrees. Water it well, watch for pests, and then place it near a sunny window during the day.
• Water when dry as before, but reduce fertilization.
• The plant should be kept in total darkness from 5 p.m. to 8 a.m. from the end of September to Dec. 15 to allow the process of changing leaf color to occur. You can carefully cover the plant with something opaque and/or place it in a closet or pantry during those hours. If any light, even indoor light, gets to the plant, it will mean green leaves only for Christmas.
• Move the plant at 8 a.m. back to the sunny location.
I hope you are successful in getting your Christmas poinsettia to rebloom next year.
-- Nancy E. Degnan
• Provided by Master Gardeners through the Master Gardener Answer Desk, Friendship Park Conservatory, Des Plaines, and University of Illinois Extension, North Cook Branch Office, Arlington Heights. Call (847) 298-3502 on Wednesdays or email firstname.lastname@example.org. Visit web.extension.illinois.edu/mg.