The plants we call Holiday Cactus may be either Christmas cactus or Thanksgiving cactus. Thanksgiving cactus (Schlumbergera truncatus) has oblong, bright green stem segments 1-1/2 to 2-1/2 inches long with 4 to 8 prominent sawtoothed marginal projections that point forward. The flowers have a short tube-like form with spreading, pointed petals, similar to trumpets. The plant bears deep pink, red, orange, or white flowers, up to 3 inches long, from late autumn to winter.
The true Christmas cactus (Schlumbergera x buckleyi) is similar but has spineless, scallop-edged segments and flowers December through March. The flowers are red-violet with 3-inch satiny-petals. The cactus can grow to 3 feet across and may have hundreds of flowers.
Both of these plants are easy to grow, requiring only well-drained soil and a sunny indoor location. After flowering, allow the plants to rest by withholding fertilizer, keeping in a cool location (about 55°F) and watering infrequently (water only when the top half of the soil is dry to the touch). After 2 months move to a warmer site, increase watering and fertilize every 2-4 weeks.
Flower buds are initiated on these plants when they are exposed to long nights or cool temperatures. In fall, reduce water and fertilizer and move the plants to a location where they will experience a 13-14 hour night and temperatures less than 65°F. If a light is turned on during the long night, the plants may experience two short nights rather than one long night and flower buds may not form. After flower buds appear (after about 6 weeks of long nights), the plants may be moved to a brighter location. Buds will open in 5-7 weeks depending on room temperature. Alternately, if the plants are kept in a cool room (never greater than 55°F), flowers will form, no matter the day length.
These holiday cactus have their origins in the jungles of Brazil. They are epiphytic which means they live on another plant, using it for support but not for nutrition (they are not parasitic). Epiphytic plants often grow in the crotches of trees, deriving their nutrition from rain, decaying organic matter and filtered sunlight.