Q. How can I get my poinsettia to rebloom?
Poinsettia, Euphorbia pulcherrima, also known as Christmas star, lobster plant, or Mexican flame leaf, has become an essential element of the holiday/Christmas scene. This colorful plant is a descendant of a 6-foot-tall shrub that grows wild in Mexico. Growers in Scandinavia and California developed the strains that have been scaled down for seasonal houseplants.
Poinsettias flower in winter and are notable for their colorful bracts (not flowers). Their greenish-yellow flowers are insignificant, but each cluster of these tiny flowers is surrounded by 10-20 attractively colored bracts (modified leaves), which look like narrowly pointed (or roughly heart-shaped) broad leaves.
Commercial growers subject their poinsettias to a strict regimen that is almost impossible to follow in the average home. All poinsettias are short-day plants--i.e., flower bud and bract formation can be initiated only by an eight-week period of no more than 10 hours of light and no less than 14 hours of total, uninterrupted darkness per day. In addition, the plants are treated with a hormone that reduces stem length. The resulting short-stemmed plants crowned by large and handsome bracts are normally sold when they are in full bloom in early winter, but may also be timed for Easter.
It is possible to grow the plant in the home to bloom again by following the steps below, although the result may not be like commercially grown plants.
- After the bracts have faded and fallen, cut top growth down to 1-2 inches from the base, and allow the potting mixture to become almost but not completely dry.
- When growth stops, keep the dormant plant at normal room temperature in bright filtered light until April; then flood it with water. The plant, still in its old pot, will soon begin to grow again.
- Two ways of proceeding are then possible. You can take 3-inch long tip cuttings from the new side shoots and root them to make new plants. Alternately, you can allow the stump of the old plant todevelop an entire new season's growth.
- If you take tip cuttings, the cut ends should be treated with water to seal in the latex, and they should then be inserted in small pots containing a mixture of equal parts of peat moss and coarse sand or perlite. Keep them in filtered light and keep mix barely moist. Allow the top two-thirds to dry out between waterings. When rooting has occurred in about 3-4 weeks, move them into pots of fresh soil-based potting mixture.
- If you choose to use the old plant instead of taking cuttings, replant the newly growing old plant in fresh soil-based potting mix. Do not use a larger pot than the original one. Bigger pots merely encourage the rapid growth of lush foliage at the expense of flowers and bracts; the result is likely to be a huge plant unrecognizable as the desired poinsettia.
- Once the cuttings or the old plant are repotted, administer monthly applications of standard liquid fertilizer until September.
- After September, give the plant no less than 14 hours of total darkness per day for eight weeks (no easy task in most homes). After about 8 weeks, bracts and flowers should start to form. Then the plant is ready to be brought out into the light.
- Because the dwarfing chemical used by professional growers is rarely available for amateur use, the resulting plant will be much taller than commercially produced poinsettias.
For tips on a variety of gardening topics, see our Plant Information Guides.
- Courtesy of NYBG Plant Information Service