The poinsettia, celebrated for its vibrant holiday appearance, is often mistakenly thought to produce red flowers. The bright color actually comes from modified leaves known as bracts, which surround the small, yellow flowers at the center of the plant. Coaxing your poinsettia to display this festive color again requires careful manipulation of its environment. This process mimics the natural conditions of its native Mexico, where the shortening days trigger the chemical changes necessary for the bracts to pigment. Successfully achieving re-coloration depends on precise timing and consistent attention to light, temperature, and horticultural maintenance.
Preparing the Poinsettia for Re-Coloring
The successful re-coloration process begins in the spring and continues through the summer. After the holiday season ends, allow the plant to rest, slightly reducing water until new growth begins to emerge in late spring. Around mid-May, the stems must be cut back significantly, typically to about four to six inches above the soil line, to encourage a dense, bushy shape. This is also the appropriate time to repot the plant into a container that is only slightly larger, using fresh potting mix to revitalize the root system.
Once new shoots appear, you can begin feeding the plant every two weeks with a balanced, all-purpose fertilizer to fuel the summer growth phase. During the summer, you should pinch back the tips of new growth occasionally, removing about an inch of the stem, to promote branching. The final pruning and pinching should occur no later than the end of August, allowing the new growth to mature before the coloring process is initiated. The plant can be kept outdoors in a partially shaded spot once nighttime temperatures consistently remain above 55 degrees Fahrenheit.
The Critical Darkness Schedule
The most demanding requirement for re-coloring a poinsettia is the precise control of its photoperiod, the daily duration of light and darkness. Poinsettias are classified as short-day plants, meaning they require an extended, uninterrupted period of darkness each night to stimulate the development of colored bracts. This regimen must be started around late September or early October to ensure a fully colored plant by the holiday season. The dark period must last for 12 to 14 hours every single night.
This means that from approximately 5:00 PM to 7:00 AM, the plant must be placed in a location where it receives absolutely no light exposure. A rarely used closet, a basement, or covering the plant completely with a large cardboard box or thick black plastic bag are effective methods for achieving this total darkness. The darkness must be absolute because even a brief flash of light, such as a streetlamp beam, a car headlight, or light from a cellphone screen, can interrupt the chemical reaction and reset the physiological clock.
Consistency is paramount during this phase, which must continue daily for eight to ten consecutive weeks. This controlled light cycle signals the plant to pigment the bracts. Once the bracts have fully colored, usually by early December, you can discontinue the darkness treatment and return the plant to its normal bright display location.
Maintaining Optimal Conditions During Coloration
While the darkness schedule is occurring, the plant’s environment during the day must also be carefully managed to support healthy growth. For the 10 to 12 hours the plant is out of darkness, it requires bright, indirect light, ideally placed near a sunny window that does not expose it to direct afternoon sun.
The temperatures must be maintained within a consistent range. Daytime temperatures should ideally be kept between 65 and 75 degrees Fahrenheit. Nighttime temperatures, while the plant is in darkness, should hover between 60 and 70 degrees Fahrenheit. Temperatures must never drop below 55 degrees Fahrenheit, as cold can cause leaf and bract drop.
Watering should be done thoroughly whenever the surface of the soil feels dry to the touch, ensuring the excess water drains completely from the pot. Leaving the plant to sit in standing water will lead to root rot, which severely compromises its ability to color up.
Why Your Poinsettia Isn’t Turning Red
If you have attempted the re-coloring process but your poinsettia remains green, the failure is almost always due to an interruption of the darkness period. The plant’s extreme sensitivity to light leaks means even a sliver of light can halt the color development process. Even a single night of interrupted darkness during the critical eight-week window can delay or prevent the bracts from changing color.
Another common issue involves temperature extremes or drafts, which can cause physiological shock. Positioning the plant near a cold window, a frequently opened exterior door, or a heat vent can cause the plant to drop its leaves and fail to color up. Furthermore, excessive nitrogen fertilization, particularly late in the season, encourages the plant to produce lush green foliage instead of the desired colored bracts. If you started the darkness treatment too late in the fall, the coloring process may simply not have had enough time to complete before the holidays.