The Christmas Cactus (Schlumbergera), a popular holiday houseplant, is a tropical epiphyte native to the rainforests of Brazil. Unlike most houseplants that bloom simply with general care, the Schlumbergera requires specific, manipulated environmental cues—primarily changes in light and temperature—to initiate the formation of its vibrant, tubular flowers. Encouraging this plant to bloom for the holiday season involves intentionally replicating the cool, short-day conditions of its natural habitat as autumn approaches. Successfully triggering the flowering cycle depends on managing three distinct factors: an extended period of darkness, a specific cooling phase, and an adjustment to its watering and feeding regimen.
The Critical Darkness Period
The primary trigger for the Christmas Cactus to set flower buds is a phenomenon called photoperiodism. As a short-day plant, it requires an extended, uninterrupted period of darkness each night to begin the process of forming buds. This nightly dark period must be consistently maintained for 12 to 14 hours for approximately six to eight weeks, typically starting in early autumn.
During the day, the plant still needs bright, indirect light to photosynthesize and generate the energy required for flowering. The darkness, however, must be absolute and continuous; even a brief flash of light from a streetlamp or television screen can disrupt the photoperiodic signal. Any interruption resets the plant’s internal clock, potentially preventing bud formation entirely. A simple, practical method for ensuring this absolute darkness is to place the plant inside a closet, under a box, or in an unused room every evening.
The Necessary Cooling Phase
A distinct cooling period significantly enhances flowering and can even substitute the need for absolute darkness, depending on the temperature. The plant needs temperatures to drop to a specific range to signal the onset of its reproductive phase. This cooling phase involves maintaining night temperatures between 50°F and 60°F (10°C to 15°C) for several weeks.
If the nighttime temperature is consistently maintained at the lower end of this range, around 50°F to 55°F, bud formation can occur even if the dark period is slightly less than the recommended 12 to 14 hours. Temperatures above 70°F (21°C) at night will inhibit bud development, regardless of the darkness routine. To achieve this necessary cooling, the plant can be moved to a cool, unheated room or placed near a window that allows for cooler nighttime air, starting in the fall.
Watering and Feeding Cycles
Adjusting the water and nutrient supply is equally important and must align with the darkness and cooling routines to support the budding process. During the six-to-eight-week period when the plant is exposed to cool temperatures and long nights to induce dormancy, water must be slightly restricted. The goal is to keep the soil slightly on the drier side, allowing the top inch or two of soil to dry out between waterings, but not so dry that the stems begin to wilt.
Fertilizer should be withheld completely during this bud-setting period, as the plant is preparing for dormancy. Excess nitrogen can encourage new stem growth instead of flowers. Once flower buds have visibly formed on the ends of the segments, the plant should be returned to a consistent watering schedule, ensuring the soil remains evenly moist but not waterlogged. A balanced or high-potassium fertilizer can be applied at this time to provide the energy needed to support the opening and development of the blooms.