Author: Extension Horticulture Specialist, Agricultural Science Center at Los Lunas, New Mexico State University.
Poinsettias (Euphorbia pulcherrima) are popular winter houseplants because they flower in mid-winter, and because their beauty is the result of bracts (persistent colored leaves) instead of flowers, their attractiveness is long-lasting. They bloom naturally under the long night conditions of winter, so it is easy for nurseries to bring them into color in time for winter holidays. The beauty of poinsettias can persist from Thanksgiving through Christmas, and sometimes even to Valentine's Day. Some gardeners are not satisfied with this long season of indoor beauty and attempt to save the plants to re-bloom the following winter. Poinsettias can be kept year after year, and they will bloom each year if you give them proper care.
When the leaves begin to yellow or when the plant is no longer desired as an ornamental, gradually withhold water. The leaves will pale and fall off. The bracts (colorful leaves just below the true flowers) will be the last to go. Figure 1 shows the parts of the plant. After all the leaves have fallen, store the plant, in its pot, in a cool (50 to 60°F), dry, dark area. Keep the plant somewhat on the dry side; water only enough to keep the stems from withering.
Figure 1. Parts of the poinsettia. The showy part, usually considered the flower, consists of the colored bracts.
In April or May, bring the plant out of storage. Cut the main stems six inches above soil level. Remove the plant from the pot and gently wash the old soil from the roots. Repot the plant in fresh potting soil that has good drainage. Poinsettias are susceptible to stem and root diseases if the soil is heavy and retains excess moisture. Soak the soil well, and then allow all excess water to drain away. Place the plant in a warm, sunny spot for renewed growth. Keep the humidity high to encourage rapid new growth. Once the plant is growing actively, apply a weak fertilizer solution (one tablespoon of a soluble fertilizer, such as 20-20-20 or its equivalent, per gallon of water) at monthly intervals.
After frost danger is past, sink the pot into a protected and sunny bed. Light shade is ideal during the hottest part of the day. Lift the pot occasionally to prevent root growth into surrounding soil. If the plant becomes root bound, repot it into a larger pot. Watch for insects and control them promptly.
Keep the poinsettia plant actively growing all summer by watering and fertilizing regularly. When the top of the soil feels dry, liberally apply water to moisten the soil completely, and allow the excess to drain away. Add no more water until the top of the soil is dry again.
To obtain a bushy plant, pinch the tips of new shoots back leaving at least two nodes on each new shoot (Figure 2). Continue pinching new shoots until late August. Remove weak stems completely, so only a few of the stronger ones develop.
Figure 2. To create a bushy plant, poinsettias are "pinched back." The tip of each twig is removed (pinched) so that nodes remain. The new shoots that arise from the nodes are also pinched.
If more plants are desired, try propagating poinsettias from stem cuttings taken in place of pinchings. When the new growth is 8 to 12 inches high, cut off 4 to 6 inches for rooting (Figure 3). Leave at least two leaves on both the cuttings and the parent stem so the plant can continue to produce food. Cut in the morning, and place the cut stem in tepid water for one hour to stop the "bleeding." Treat the base of cuttings with rooting hormone to increase the chances for success. Place cuttings in a well-drained, moist rooting medium, such as a half perlite, half peat moss mix. Keep humidity high for rapid rooting. Place cuttings in bright, but not direct, light. Pot the newly rooted cuttings in a well-drained soil when the new roots are about 1/2 inch long. Care of these plants is the same as care for the parent plant.
Figure 3. Poinsettia softwood cuttings, 4 to 6 inches long.
The parent plant and all rooted cuttings will bloom at the same time. The thicker cuttings will produce larger blooms. Make as many cuttings as desired until late August, but remember, only strong stems produce strong plants.
As cool fall weather begins, take the plant inside to a south window with full sun. Poinsettias do best in full fall sun and the bracts (colored leaves below the flowers) obtain their deepest color in good light. Ventilation is important, but keep the plant away from drafts. Drafts, as well as low temperatures, waterlogged soil, and drought, can cause the lower leaves of the poinsettia to turn yellow and fall from the plant. Night temperatures of 60 to 65°F and day temperatures up to 75°F are recommended. If the night temperature is too high or too low, the plant is likely to flower later.
The poinsettia is known as a true short-day (or long-night) plant. This means that the plant must be in total darkness for about 14 hours out of every day for a four-week period to form flower buds. Beginning in late September or early October, make certain the poinsettia receives no artificial light after nightfall. Even brief periods of light from a single light bulb for one night may be enough to delay or interfere with flowering. If possible, keep the plant in a room without lights, in a dark closet, or under a fully light-proof cover from about 5:00 p.m. to 7:00 a.m. every day for four weeks.
Remember to put the plant in a sunny window in the daytime, and drench the soil when the surface is dry. It will probably need watering less often now. Continue fertilizing it monthly until mid-December. The opened flowers last longest at about 65°F.
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Revised and electronically distributed December 2009, Las Cruces, NM.