After I sat down to write this article about one of my favorite plants, I came across a very informative discussion on the topic of the Schlumbergera in the Houseplants Forum here on ATP. I decided rather than reinventing the wheel, I'd enlist the help of one of the contributors to that discussion. The following is some of the information she shared about Schlumbergera and getting them to bloom for the upcoming holiday season.
Sherry (ATP member: keystone) provided much excellent information about the holiday cacti including an interesting story about how she became involved with the Schlumbergera. She writes:
Several years ago I sort of unofficially inherited a Schlumbergera x buckleyi--the old-fashioned Christmas Cactus--from my great-grandmother after she passed. It was huge. I had spotty blooms on it for several years. Then one year I put it down in the basement for Christmas just to get it out of the way of the festivities because it was so large. When I brought it back upstairs, it was loaded with blooms! I was hooked!
Thanksgiving cacti are mostly hybrids that have a majority of the species S. truncata in their genetic background. The phylloclades, or stem sections, have little spikes or hornlike structures on them. Commercial growers like them because they have an upright growth habit and can be more easily crowded together. They bloom, as the name suggests, around Thanksgiving or later. The flowers are held at an upright angle resembling a bird in flight. They come in a variety of colors from white to red to yellow.
The true Christmas Cactus is a hybrid of S. truncacta and S. russelliana, the initial cross having been made many years ago. It is rarely found for sale today and is usually known as S. x buckleyi. This is the one that is passed down from generation to generation. There are many examples of x buckleyi in existence that are over 100 years old. It has scalloped, rounded phyllocades, a pendant growth habit, and is suitable for hanging baskets. It blooms quite a bit later than the Thanksgiving cactus, usually in January or February. The roundish, bell-shaped blooms hang down from the phyllocades. These plants are mostly hot pink and fuschia with copper tones although white ones are known to exist.
The Thanksgiving and Christmas cacti can be crossed back and forth between each other. The plants you find at the grocery store and most nurseries at Thanksgiving may show the characteristics of both types of holiday cacti or of one predominantly more than the other.
A frequently asked question about Schlumbergera is how to get them to bloom year after year. Over the course of time, I've had mixed results when it comes to getting these plants to bloom for the holidays. I do know that they are reported to be thermo-photoperiodic, meaning their bloom initiation is triggered by a combination of day length and temperature, with day length being the primary trigger. Sherry's advice below appears to be an almost foolproof remedy for bloomless plants.
The most important factor in getting Schlumbergera of any type to bloom is the period of short days, long nights. If you are hoping to see your Christmas Cactus bloom, you must have it in a room that does not have any lights on after dark. Ideally, this should begin by the middle of September or earlier. It has been said that even 5 footcandles of light can keep a plant from budding (a footcandle is how bright the light is one foot away from the source). When the nights get to be around 14 hours long, the plant will know to initiate buds. You can even put the plants in a dark basement for 3-4 weeks with no harm. By the end of that period you should see the buds forming as little balls on the end of the phyllocades.
Some people say you have to give them a cooling-off period or withhold water to get buds. I do not find that necessary, but if you are doing those things and getting flowers, I don't argue with success. My plants routinely form buds in a 70º environment and I water as usual. If you give a cooling treatment to a white or yellow Schlumbergera, your plant may have a pinkish tint when it blooms. Overwatering will cause bud drop as will subjecting the plant to wide temperature swings, the latter being the main cause of bud drop when new plants are first brought home from the store.
Sherry's Schlumbergera collection consists of around 25 plants and quite a few seedlings. She prefers the hard-to-find cultivars and bicolor flowers. Some of the cultivars in her collection include Beach Dancer, Dark Marie, Peaches and Cream, Sunset, Thor Tenna, Thor Vida, Samba Brazil, Polka Dancer and Sunset Dancer. She suggests Caribbean Dancer as a great plant for the beginner. It is bright red, very vigorous, and exceptionally long-blooming.
To learn more about the genus Schlumbergera, Sherry recommends the book, Christmas Cactus - The Genus Schlumbergera And Its Hybrids by A. J. S. McMillan and J. F. Horobin.