With a little coaxing -- and a lot of discipline -- you can get your poinsettias and Christmas cacti to bloom for this holiday season. Those gorgeous red or white poinsettias actually don't produce showy flowers. Their splashes of color are brightly hued leaf bracts, and the plants require special care to produce them.
If you have a poinsettia from last Christmas, keep its soil moist and fertilize it every seven to 10 days with one-half teaspoon of a soluble fertilizer such as 15-15-15 in a quart of warm water. These fertilizers are available at any garden center.
Poinsettias need long, dark nights to form their colorful bracts. Starting in October, keep your poinsettia in a completely dark place between 5 p.m. and 8 a.m. every night until Thanksgiving.
"During these hours, you must stay out of the closet or room where you're keeping the plant," says J. Robert Nuss, professor of ornamental horticulture in Penn State's College of Agricultural Sciences. "Even peeking in or briefly turning on the light will upset the process."
Between 8 a.m. and 5 p.m., set the poinsettia in a warm, sunny window. Soon you will see leaves and flower buds forming. "Poinsettias are sensitive to sudden changes in temperature and improper watering or light conditions," says Nuss. "Keep the temperature between 60 and 75 degrees, even during the times when the plant is kept in the dark."
After Thanksgiving, you can put your poinsettia out on display. Continue watering, fertilizing and giving it plenty of sun. Beginning in March, stop fertilizing and gradually reduce water to about a cupful once a week, storing the dormant plant in a cool, well ventilated place out of direct sunlight until May.
In May, cut the plant back to three to five inches high, start watering more and fertilizing regularly, and return the plant to a sunny window. "You can move poinsettias outside into light shade when nights are at least 60 degrees Fahrenheit," says Nuss. "To shape them, pinch back each shoot once during the summer."
When cool nights start in late August, bring your poinsettia inside to a sunny window in a room with temperatures no higher than 60 to 62 degrees Fahrenheit. Starting in October, begin the regimen of long, dark periods once again. "By following all these steps, you can keep poinsettias for years," says Nuss.
Christmas and Thanksgiving cacti are a little easier to care for and produce filmy, orchidlike flowers in red, white or pink. Some of these cacti also will flower at Easter.
"One of the main things to remember about these plants is that they're not like typical cacti," says Nuss. "They require as much water as other houseplants. Their soil should be kept moist but not soggy."
To develop blooms, these cacti require cool temperatures in the fall. If you need to bring your flowering cacti inside before October, keep them out of bright light in a cool room.
Bring them to a sunny window as soon as buds start to show. "If your cactus starts to drop its buds, the plant may need repotting, more sunlight or a lower temperature," says Nuss. "They seldom flower well at temperatures above 70 degrees Fahrenheit."
After the cactus stops blooming, keep it in a cool, sunny window. In summer, put it outside in light shade and leave it there as long as possible into the fall.
"Holiday-flowering plants are more challenging than a lot of houseplants," says Nuss. "But that adds to the enjoyment. It can be very satisfying to coax them into flowering."
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