Despite holding the official title of most popular potted plant, the familiar poinsettia remains full of surprises. Native to the hillsides of western Mexico, where they grow wild as shrublike plants reaching 15 feet tall, poinsettias -- after decades of breeding -- have been transformed into the colorful compact house plants that are ubiquitous during the holidays.
The brightly colored "flowers" of the poinsettia (Euphorbia pulcherrima) are actually petal-like leaves, called bracts -- the true flowers are the tiny beadlike yellow and green parts, called cyathia, at the center of the bracts. Unlike many flowering plants, which require long, sunny days to induce flowering, poinsettias produce their colorful bracts as the nights lengthen.
Once available only in red, poinsettias now come in a range of colors that includes pink, peach, yellow, and white. Some cultivars have marbled or speckled bracts while others have wavy or ruffled bracts that resemble pom-poms.
For healthy, long-blooming plants, choose poinsettias with tightly grouped cyathia at the tips of the stems and bracts that are fully colored (bracts that are greenish around the edges will never color fully). Unless you're purchasing poinsettia topiaries, which are trained to resemble trees, select sturdy plants with stiff stems and lush green leaves all the way to the soil.
Caring for Poinettias
In winter, during their bloom time, keep poinsettias in bright but indirect light (six to eight hours of filtered sun daily) and away from drafts and heaters, which can cause the leaves to drop. Plants thrive at room temperatures during the day (60 degrees to 75 degrees) and prefer slightly cooler nights (60 degrees to 65 degrees). Poinsettias are very cold-sensitive, so keep them away from chilly windows. Water plants only when the soil is dry.
In spring, after the bracts become a muddy green, cut the plants back to about 6 to 8 inches tall; continue watering, and begin fertilizing biweekly with a balanced all-purpose fertilizer for flowering plants.
In summer, repot plants in fresh soilless potting mix in slightly larger pots, and move outdoors if desired to a spot with morning sun. Continue watering and biweekly fertilizing. Prune plants to encourage a bushy, compact habit.
How-To Rebloom Poinsettia
Making poinsettias rebloom is a challenge. To induce flowering in time for the holidays, continue watering plants but stop fertilizing in early fall. Beginning on October 1, move the plants to an absolutely dark room or closet each night, or place them under a box so they receive at least 14 hours of uninterrupted darkness per day -- even light from a lamp can disrupt the flowering. Depending on the cultivar, colorful bracts should develop in six to 10 weeks.
Poinsettias, native to the hills of western Mexico, are named for Joel Roberts Poinsett, the first U.S. ambassador to Mexico (1825-1829), who introduced them to the United States.