Christmas and Thanksgiving Cacti
These are the plants that beckon us from the flower departments of the big box stores, and the grocery stores, and the flower shops. When these plants are 'happy' they seem to live and please generations of families. And then they can be fussy.....
Here is good advice and information from Ward Upham at K State:
Christmas Cactus (Schlumbergera bridgesii) and Thanksgiving Cactus (Schlumbergera truncata) are epiphytes native to the jungles of South America. Epiphytic plants grow on other plants and use them for support but not for nutrients. Though these cacti are different species, they will hybridize and produce varying stem shapes. Christmas cactus normally has smooth stem segments, and Thanksgiving Cactus has hook-like appendages on each segment.
Both of these cacti prefer bright indirect light. Too much sun can result in the leaves turning yellow. Common household temperatures are fine. Soil should be kept constantly moist but not waterlogged. Give them a light fertilization every other week. Blooming will normally cease in late winter to early spring, but continue to keep them moist and fertilized until fall. During the fall, stop fertilizing, and give the plants only enough water so the stems do not shrivel in order to encourage flower bud formation.
Though these plants seem to flower best if kept a little pot bound, flowers will diminish if they are too crowded. If you haven't repotted in several years, or if you notice a decrease in flowering from the previous year, move the plant to a larger pot in the spring. If possible, move the plants outside for the summer. Choose a shady spot because these plants will not tolerate full sun. Leave the plants outside until frost threatens.
Normally, the plants will have received enough cool nights in the 50- to 55-degree range that flower buds will have formed. However, if they haven't, subjecting the plants to nights greater than 12 hours long and temperatures between 59 and 69 degrees can also generate flowers. Twenty-five consecutive long nights is enough for flower initiation. Place the plants in an unused room or cover them with a dark cloth or cardboard box to insure that they receive uninterrupted darkness. After the flower buds have formed, it takes an additional nine to 10 weeks for flowers to complete development and bloom.