What it actually is
The Christmas cactus, Schlumbergera, is an epiphyte from the Brazilian Atlantic forest: it grows in tree forks, in a little humus, in shade and humidity.
Treating it as a desert cactus — full sun, drought, mineral compost — is the first cause of failure.
Why it will not flower
Flowering is triggered by photoperiod: six to eight weeks beforehand it needs long, unbroken nights — around thirteen hours of complete darkness — and cool temperatures, near fifteen degrees.
A lamp switched on in the evening is enough to cancel the signal. That is the most common explanation for a healthy plant that never blooms.
Once buds have formed, stop moving and turning it. A change of orientation makes it drop its buds within days.
What it wants
Bright light without direct sun, a light free-draining mix, water when the surface is dry — never standing water in the saucer. A drier, cooler rest after flowering, then normal care.
Christmas, Easter or Thanksgiving
Three related species flower at different times, and the trade confuses them. Tell them apart by the segments: toothed and pointed on the Thanksgiving cactus, rounded on the Christmas cactus, smooth and toothless on the Easter cactus.
our piece on flower symbolism places these plants among those that mark the turning of seasons.