Otherwise know as "How do I get this little sucker to bloom at the RIGHT time of year!"
Christmas cactus blooms are triggered by short days and/or cool nights. Buds form in late October or early November when daylight is less than 12 hours. Buds also will set when night temperatures are 55-60 degrees.
To make absolutely sure your plants will bloom at Christmas, you should have started your light control in October.
It's difficult to control night temperatures, but you can provide uninterrupted overnight darkness. Place the plant in an unheated closet for 13 hours a day beginning in October and continue until color appears. The plant will bloom in six to eight weeks. That's traditional advice.
However I say,
Some people do put their plants in a closet every night with no problem. But Christmas cacti can be finicky about being moved frequently, and react by shedding their buds. An alternative is to leave your plants in place and cover them with paper bags at night. That's just me though (shrug)
Regardless, once flower buds do appear, give them bright light, or even a bit of direct sun, and daytime temperatures between 60 and 70 degrees. Keep the soil barely moist and pinch off spent flowers.
Christmas cactus, Schlumbergera bridgesii, is a sprawling, jointed Brazilian native that produces 3-inch tubular blooms in pink, red, purple, fuchsia or white. It needs well-drained, porous, organic soil and bright light. Winter sun is OK, but summer rays burn the foliage.
Water when the top of the soil is dry. Apply a balanced fertilizer during the growing season. Flush the soil occasionally to prevent salt buildup. Stop or reduce fertilizing in fall.
Prune after it blooms, removing one or two of the flattened stem segments that act as leaves (phylloclades). This encourages branching and future blooms.
Bud drop is caused by above-90 temperatures, sudden temperature changes, dry soil or poor light after buds set. Ethylene gas, produced when there's poor ventilation near a heater or fireplace, also causes bud drop. Christmas cactuses survive temperatures from 35 to 100 degrees, but grow best in 65- to 85-degree temperatures. They can live more than 20 years.
After Blooming
Once all the blooms fade, move your Christmas cactus to a cool room to rest. Be sure to protect the plant from frost and freezing temperatures. The cactus may melt away if temperatures drop to the low 30s.
Let the soil go dry between waterings. Don’t ever let the soil stay soggy, especially during cooler weather, as root rot can be lethal. But if the fleshy stems show signs of shriveling, water right away.
