The poinsettia, Euphorbia pulcherrima, is a popular holiday decoration. The vibrant red, pink, or white structures are not true flower petals; they are modified leaves called bracts that surround the small, inconspicuous yellow flowers, or cyathia. Coaxing these bracts to change color again after the holiday season requires a dedicated, year-long approach that mimics the plant’s native environment. Successfully reblooming a poinsettia is a rewarding horticultural challenge.
Preparing the Poinsettia for Reblooming
Once the decorative bracts have faded, typically in late winter, prune the stems back significantly to approximately four to six inches above the soil line. This pruning encourages new, healthy side shoots necessary for a full, well-branched plant the following year.
Following the trim, the plant may benefit from repotting into a slightly larger container using fresh potting soil. During the spring and summer, provide bright, indirect light and warm temperatures (65 to 75 degrees Fahrenheit). Fertilize every two to four weeks, and continue to pinch back the tips of new growth until early September to encourage a denser, bushier shape.
The Science Behind the Color Change
The transition from green leaves to colored bracts is governed by photoperiodism, a plant’s response to the relative lengths of daylight and darkness. Poinsettias are “short-day” plants, meaning they require uninterrupted darkness each night to trigger pigment production in their bracts.
The actual mechanism responds to the length of the night; the continuous dark period initiates hormonal changes. Even brief exposure to low-intensity light will break the dark cycle and prevent the color change. This sensitivity makes manipulating the light cycle the most important step in forcing a rebloom.
Executing the Critical Dark Treatment
The specialized regimen to initiate bract coloring must begin around the autumnal equinox (near September 21st) and continue for eight to ten weeks. During this period, the plant must follow a precise schedule of light and darkness every day, requiring at least 14 hours of absolute, uninterrupted darkness daily.
This means the plant must be shielded from all light sources from late afternoon until mid-morning. A dark closet, a spare room, or a large cardboard box can serve as an effective blackout chamber. The temperature during this nightly dark period should be 60 to 65 degrees Fahrenheit; temperatures consistently above 70 degrees may inhibit color development.
For the remaining 10 hours, immediately return the poinsettia to a location with bright light to photosynthesize. Consistent watering and reduced fertilization should continue during this phase. Rotating the plant daily helps ensure uniform bract development. This strict cycle must be maintained until the bracts show significant color, typically by late November or early December.
Maintaining the Color Change
Once the bracts have successfully developed color, the strict dark treatment can be discontinued, and the plant is ready for display. The focus shifts to maintaining the vibrant color and preventing the premature drop of leaves and bracts.
Ideal display conditions involve placing the poinsettia in a sunny area that receives ample daylight, avoiding locations near heat vents or cold drafts. Keep the plant at a moderate, consistent room temperature (65 to 70 degrees Fahrenheit) to prolong the display life. Water only when the soil surface feels dry to the touch, ensuring the plant never sits in standing water.