I just call them "holiday" cacti because they rarely bloom on their assigned holidays unless given a lot of manipulation.
Christmas cactus, usually called S. bridgesii, has blunt stem margins and bright purplish-pink flowers.
Easter cactus (Rhipsalidopsis gaertneri), like Thanksgiving cactus, has sharp teeth on its stems, but the stem joints and flowers are short, and the plants are upright. The flowers are red.
DON’T GIVE HOLIDAY CACTI DESERT CONDITIONS
Holiday cacti are much easier to grow than to name. They have a common ancestral root in the moist, tropical jungles of Brazil. There, they grow nestled in the partly decayed organic matter that accumulates in the forks of trees, with mist-charged air taking the edge off the tropical heat and leafy treetops softening the tropical sun.
Now let's try to bring these conditions to a potted holiday cactus. The plants surely enjoy frequent spritzing from a mister, especially when they are inside the house for winter. They like bright light, but do not need the sunniest windows.
The potting mixture for these cacti should be well-fortified with organic matter. Peat moss or one of the coarse fibers, such as osmunda or coir used for epiphytic orchids, are good choices of organic materials that aerate a potting mixture while at the same time retaining water.
REST THEM, FOR FLOWERS
Holiday cacti need a short rest period at summer's end as a prerequisite to bloom. That rest period is fulfilled by some combination of cooler temperatures and shorter days. Temperatures in the 50's will bring on flowering no matter how short the days are. Between 60 and 75 degrees, days need to be shorter than about 13 hours before flowering occurs.
You could even get these plants to bloom in summer by shading them so they see only about 10 hours of light each day for about four weeks. Watch out for too much warmth though or the flower buds will drop.
By the way, although it's conventional to talk about "day length," what's really important is the length of the daily dark period. A streetlight or even a light switch briefly turned on can shorten the dark period and reverse the flower-inducing effect.
HOLIDAY CACTI AND ME
The first holiday cactus I had only sporadically coughed forth a few colorful blossoms, despite good growing conditions. True, that old cactus suffered neglect, including two drops to the ground in its hanging planter. But neglect was payment, rather than cause, for its poor performance. The old plant was too floppy and messy for my taste, so after 10 years, I walked it to my compost pile.
A gardening friend gave me my next holiday cactus, and that one bloomed abundantly for years. Every winter, it was bedecked with large flowers, each having rose-brushed, white petals that arched back like wings from its floral tube, inside of which ran a pencil-thin line of magenta. Alas, that plant is no more, having succumbed to scale insects.
A year ago, I propagated a new holiday cactus, now in bloom. The keys to success: Get a good variety, give it good growing and then flowering conditions, and keep an eye out for scale insects.
Lee Reich writes regularly about gardening for The Associated Press. He is the author of numerous gardening books, including “Weedless Gardening” and "The Ever Curious Gardener: Using a Little Natural Science for a Much Better Garden.” He blogs at http://www.leereich.com/blog. He can be reached at email@example.com.