The poinsettia (Euphorbia pulcherrima) is a tropical shrub native to Mexico and Central America. While it can reach heights of up to 13 feet in its native environment, it is cultivated as the world’s most popular potted flowering plant sold during the winter holiday season. The Aztecs originally called the plant cuetlaxochitl and used its colorful bracts (modified leaves) to produce dye. Today, its association with Christmas is due to precise horticultural timing, allowing growers to produce millions of perfectly colored plants for the late-year market.
Starting New Plants from Cuttings
Commercial poinsettia cultivation begins months before the holiday season, relying on vegetative propagation rather than seeds. This process starts in late spring or early summer when small stem cuttings are taken from stock plants. These cuttings, usually 2 to 2.5 inches long, are the foundation for the next generation of finished plants.
Once harvested, the cuttings are treated with a rooting hormone, such as Indole-3-butyric acid (IBA), to stimulate root development and ensure uniform growth. They are then “stuck” into a specialized growing medium, requiring a consistently warm environment, ideally 70–72°F. High humidity, maintained by misting or fog systems, is provided for the first few weeks to reduce stress until a robust root system develops, which takes about three to four weeks.
Shaping the Poinsettia (The Vegetative Phase)
After the cuttings have rooted and been transplanted into their final pots, the focus shifts to developing the full, bushy shape consumers expect. Unlike plants that naturally branch easily, poinsettias require a technique called “pinching” or “stopping” to promote lateral growth. This process involves the grower manually removing the growing tip of the plant during the summer months.
Pinching removes apical dominance, a hormonal inhibition caused by the main stem’s growing point that prevents lower buds from developing. Removing this tip forces the lateral buds below the cut to break dormancy and grow outward, creating multiple stems. The number of stems left after the pinch (often five to seven nodes) directly determines how many colorful bracts the final plant will have, impacting its aesthetic quality.
Inducing the Holiday Color (Photoperiod Control)
The final stage is the induction of the plant’s holiday color, which relies on strict photoperiod control. Poinsettias are short-day plants, requiring a specific duration of uninterrupted darkness each night to trigger flower bud formation and bract coloration. This induction process begins around late September or early October to ensure the plants are fully colored by the holiday season.
Growers must subject the plants to approximately 14 to 14.5 hours of continuous, absolute darkness every night for eight to ten weeks. Even a brief exposure to low-intensity light, less than two foot-candles, can interrupt the chemical signals and reset the coloration process. This control is often achieved in commercial greenhouses using automated black cloth systems that cover the plants completely at dusk and retract at dawn.
Temperature management is precisely controlled during this phase to optimize color development. Night temperatures are maintained around 62–64°F during the initial induction period for rapid development. Once the bracts begin to form, slightly warmer temperatures (67–68°F) favor their rapid expansion. As the plants near shipping, night temperatures may be dropped to 62–63°F to intensify the final color and prepare the plants for transport and retail display.