The poinsettia, or Euphorbia pulcherrima, is a plant native to Mexico and Central America. It is recognized globally as a symbol of the winter holidays and is one of the highest-selling potted plants in the United States and Canada leading up to Christmas. Its widespread appeal stems from its striking coloration, which provides a dramatic contrast to the muted tones of mid-winter.
The Spectrum of Poinsettia Colors
While the image of a poinsettia is most often a vibrant red, breeders have cultivated a wide range of natural colors. The plant’s colorful parts can be found in shades of white, cream, and pale yellow. Other options include soft pinks, salmon, and deep burgundies, providing a spectrum of tones within the red family.
Many unique cultivars feature marbled, speckled, or bi-colored patterns, such as varieties with creamy white edges on deep pink or red bracts. Some varieties have been bred to feature orange or pale green coloration, expanding their use for autumn displays. Note that any blue or purple poinsettias found in the market are typically cream-colored varieties that have been artificially dyed or spray-painted.
Bracts, Not Blooms: Identifying the Colored Parts
The vibrant, showy parts of the poinsettia are not flowers. These colorful structures are actually modified leaves called bracts, which are designed to attract pollinators. The plant’s true flowers, known as cyathia, are small, inconspicuous, cup-shaped structures clustered at the center of the bracts.
The cyathia are typically yellow-green and lack petals and sepals. When selecting a poinsettia, the freshness of the cyathia indicates the plant’s longevity. A plant with green-tipped or red-tipped cyathia is younger than one with yellow, pollen-shedding flowers. Once the true flowers shed their pollen, the colorful bracts typically begin to drop soon after.
The Biological Trigger for Color
The mechanism that causes the poinsettia’s bracts to change color is called photoperiodism. Poinsettias are classified as “short-day” plants, meaning they require a specific duration of uninterrupted darkness each day to trigger pigment production and initiate flowering. This long-night requirement naturally aligns with the shortening days of late autumn and early winter.
To achieve coloration, the plant must receive approximately 12 to 14 hours of continuous, total darkness every 24 hours for several consecutive weeks. This light deprivation triggers a hormonal response that stimulates the synthesis and accumulation of anthocyanins, the pigments responsible for red, pink, and purple colors. Simultaneously, chlorophyll production in the upper leaves decreases, allowing the pigments to become visible as the bracts change color. Even a brief flash of light during the dark period can interrupt this process and delay or prevent the change in color.
Maintaining and Re-Coloring Your Poinsettia
After the holiday season, a poinsettia can be kept healthy and re-colored for the following year. Throughout the spring and summer, the plant should be kept in a sunny location with daytime temperatures between 65°F and 75°F. Regular watering and fertilizing are necessary to encourage new growth, and the stems should be pruned back to about six inches in April.
The process of forcing the plant to re-color must begin in early autumn, around the end of September. The plant must be subjected to 13 to 15 hours of absolute darkness every night, usually by placing it in a dark closet or covering it with an opaque box. During the remaining 9 to 11 hours of the day, the plant requires bright light. This daily dark treatment must continue for eight to ten weeks, until the bracts show a distinct color change, at which point the plant can be returned to normal light conditions.