Christmas Cactus - Schlumbergera

General Information
Schlumbergeras are epiphytic (tree-perching) with arching or pendulous flat stems that somewhat resemble long leaves and produce more or less asymmetrical flowers.  They belong in the Cactus family. Schlumbergera truncata, know as the Crab Cactus or Thanksgiving Cactus, has stems with segments or joints 1½ to 2½ inches long, each with two to four sharp teeth along their margins and at their corners.  The asymmetrical blooms are in various shades of pink or red.  The petals spread backwards. The Christmas Cactus, S. Buckleyi, is considered the easiest Schlumbergera to grow.  The apexes of its leaf joints are without sharp teeth. The blooms are purplish-pink and have pink stalked stamens.  The other parent of the Christmas Cactus is S. Russelliana.  With nearly symmetrical, magenta blooms that close at night, it blooms much less freely than other kinds. The Thanksgiving Cactus, Schlumbergera truncata bi-color, blooms in fall, earlier than the Christmas Cactus.  Its flowers have white perianth tubes, and petals with deep rose-pink, salmon-pink, and light crimson blooms.

General Culture
Old-time favorites as house plants and as greenhouse plants, these cactus succeed in loose, porous soil that contains an abundance of rough leaf mold or other coarse organic material. 
Feeding of the Schlumbergera is done during the plant's active growth cycle, when new stems (phylloclades) are formed (from April to September).  Feed with a water-soluble 15-30-15, or equivalent.  During this time the soil should be kept slightly moist, not wet.  From October thru March, the soil is allowed to dry to the touch between watering, even when in bloom. 
Cool night temperatures along with the short days of fall and winter are the keys to successful blooming.  During fall and winter, as the days get shorter in daylight period, keep the plant at 50o to 55o F at night, and 5o to 10o warmer during daylight hours. Temperatures below 50o F may inhibit flower bud induction and initiation.  Morning sun, with filtered bright light for the balance of the day, will prolong the bloom (as long as night temperatures are cool). During late spring and through the summer months, place the plant outdoors in a location that receives morning sun or filtered bright light (no hot sun).  Water to keep the soil slightly moist while the plant is producing new stems.

It is not unusual to have the Christmas cactus bloom throughout the winter, if kept in cool temperatures and provided no additional light at night.  I have had many Schlumbergera truncata and S. Buckleyi complete four blooming cycles in one year. Another experience I have had with Schlumbergera truncata, plants approximately 2 ft. in diameter placed on a cool, east facing window sill during fall and winter, bloomed only on the side closest to the cool window.  The stems on the side reaching out into the room where the night temperature was 8 to 10 degrees warmer than the side closest to the window (generally 50o to 55o F) never set flower buds.

Repotting an Older Plant
An older, well-established Schlumbergera may be growing in what appears to be "concrete" — soil that has turned out be hard as a rock.  The organic matter in the soil mix has broken down and has no consistency, leaving nothing but clay and sand particles.  Although it is not necessary to repot a Schlumbergera with any frequency (I've had one in the same soil for some 15 years) once the soil breaks down and the plant has become overgrown, transplanting will be beneficial.

To transplant a Schlumbergera, after the last blooming cycle of late spring, slip the plant from its older pot, crumble the "concrete" soil from the fragile root system and repot in a cactus mix with new organic matter.  I blend a prepared cactus mix containing a coarse, sharp sand with milled sphagnum peat moss at a ratio of 5 parts cactus mix to 1 part organic matter.

After potting, let the plant set in the new mix for up to two weeks before watering in order to repair the root tissue damaged which occurred when the soil was removed from the roots.  Callus tissue (scabbing) should be allowed to occur on wounded tissue before being exposed to moisture.  After two weeks, water thoroughly and then keep the soil mix only damp to the touch.  DO NOT OVER WATER.

April Pruning
Without exception, all of my Schlumbergera need pruning or pinching each spring.  Due to light conditions, my plants always grow more on one side than another, thus giving the plants a look as if they were growing out of their pots to one side.  To get my plants back in balance, I pinch or prune the lopsided stems (those which are extra long when compared to others) back to a node so when finished, all of the plants are equal in size on all sides.  In many cases, this necessitates pruning back to older stems tissue (browned bark-like tissue).  I use all of the clippings to start new plants.

Propagation
Cuttings of one or more stem segments (joints which look like leaves) can be rooted in slightly moist sand.  Gently break the cutting at the stem joint, apply rooting hormone on the base of the cutting, and place the base of the cutting no more than ½-inch deep into the propagation medium.  Keep the medium only slightly moist.  The cuttings will develop roots in two to three weeks under normal growing conditions.