The poinsettia is a popular decorative plant often associated with the holiday season. Native to tropical regions in Mexico, it is highly sensitive to temperature fluctuations and cold conditions. The striking red, pink, or white parts are modified leaves called bracts, often mistaken for flowers. Maintaining the correct temperature is the most important factor for keeping this tropical species healthy and preserving its vibrant color.
The Optimal Indoor Temperature Range
Poinsettias thrive best when their indoor environment mimics the warm, consistent temperatures of their native habitat. The ideal daytime temperature range for maintaining the plant’s health and color is between 65°F and 75°F (18°C to 24°C).
Keeping the temperature consistent within this range helps the plant retain its foliage and prevents the premature dropping of the colored bracts. A slight drop in temperature overnight is beneficial.
The preferred nighttime temperature should stay between 60°F and 70°F (15°C to 21°C). Allowing the temperature to fluctuate wildly throughout the day and night can cause stress, often resulting in the plant dropping its leaves.
Cold Tolerance and Immediate Damage Thresholds
The poinsettia has a very low tolerance for cold temperatures, which is the most common cause of damage for indoor plants. The immediate danger zone is any temperature falling below 50°F (10°C). Exposure to temperatures below this threshold, even for a short period, can cause cold shock and severe tissue damage.
When exposed to cold, the plant’s cells can be damaged, leading to symptoms that may not appear until days later. These symptoms include lower leaves turning yellow and dropping, or the colorful bracts becoming discolored or wilted. To protect the plant, it should be kept away from cold drafts coming from open windows, doors, or air conditioning vents. During transport, it should be tightly wrapped to prevent cold air from infiltrating the foliage.
Temperature Requirements for Re-blooming
Getting a poinsettia to produce new colored bracts requires a strict regimen of light and temperature control. This process is necessary to trigger the physiological color change. Starting in late September, the plant requires a cool, consistent nighttime temperature.
The ideal temperature range to encourage the coloring of the bracts is a nighttime low of 60°F to 65°F (15°C to 18°C). If the nighttime temperature rises above 70°F to 75°F (21°C to 24°C), the plant may delay or prevent the color change. This cooler temperature, combined with 14 to 15 hours of complete, uninterrupted darkness daily, signals the plant to begin its reproductive cycle.