The holiday cactus — this one is a Thanksgiving cactus, Schlumbergera truncata, identifiable by the pointed, serrated edges on its stem segments — is not a true cactus. It's a tropical forest plant from Brazil, and it grows on trees rather than in desert soil. That origin explains almost everything about how to keep it alive and get it to bloom.
It wants more water than a desert cactus, but not as much as a leafy houseplant. Water thoroughly when the top inch of soil goes dry, then let it drain completely. It does not want to sit in water. During active growth, that might be every seven to ten days; in winter after blooming, pull back and let it stay drier for a month or two.
Light should be bright but indirect — a few feet back from a window, or an east-facing exposure. Direct afternoon sun bleaches the stems and stresses the plant.
Blooming is triggered by two things working together: cooler temperatures (around 50–55°F at night) and longer darkness (twelve to fourteen hours). In practice, this means a plant sitting near a window in a room that cools down in autumn will often bloom without any intervention. Moving it to a garage or a cool porch for six weeks in September or October and then bringing it back in works reliably if your house stays warm year-round.
One common failure: putting it somewhere it gets hit by artificial light at night — a streetlight through a window, a lamp left on. Even a few minutes of light disrupts the darkness cycle and delays or prevents blooming.
After it blooms, let it rest. Reduce watering, skip fertilizer, and leave it somewhere cool for a month. Then bring it back into regular care and it will set buds again the following season.