Holiday Cactus Brings the Gift of Color
Schlumbergera is a small genus of cacti (of the family Cactacaea) with six to nine species found in the coastal mountains of south-eastern Brazil. In the wild, the species of Schlumbergera grow either on trees (epiphytic) or on rocks (lithophytic) in habitats that are generally shady with high humidity. Most species of Schlumbergera have stems which resemble leaf-like pads joined one to the other and flowers which appear from areoles (small light- to dark-colored bumps) at the joints and tips of the stems. They are leafless, the green stems acting as photosynthetic organs (carrying out the process of photosynthesis).
Schlumbergera truncata was in cultivation in Europe by 1818, and S. russelliana was introduced in 1839. The two species were deliberately crossed in England by W. Buckley, resulting in the hybrid now called S. × buckleyi, first recorded in 1852. By the 1860s, a substantial number of cultivars were available in a range of colors and habits, and were used as ornamental plants. They fell out of favor until the 1950s, when breeding resumed in Europe, North America, Australia and New Zealand. New plants were produced by crossing among the species and existing cultivars of S. truncata, S. russelliana and the hybrid S. × buckleyi.
Common names for these cacti generally refer to their flowering season. In the Northern Hemisphere, they are called Christmas cactus, Thanksgiving cactus, crab cactus, and holiday cactus.
The cultivars of the Christmas cactus fall into two main groups:
The Truncata Group contains all cultivars with features derived mainly from the species S. truncata: stem segments with pointed teeth; flowers held more or less horizontally, usually above the horizontal, whose upper side is differently shaped from the lower side (zygomorphic); and yellow pollen. Flowers come in red, purple, pink, white and yellow. These cultivars generally flower earlier than members of the Buckleyi Group and, although common names are not applied consistently, may be distinguished as Thanksgiving cactus, crab cactus or claw cactus.
The Buckleyi Group contains all cultivars with at least some features clearly showing inheritance from russelliana: stem segments with rounded, more symmetrical teeth; more or less symmetrical (regular) flowers which hang down, below the horizontal, in bright magenta red to pink; and pink pollen. These cultivars generally flower later than members of the Truncata Group and are more likely to be called Christmas cactus.
In the United States, cultivars are propagated in large numbers for sale before Thanksgiving and are often called Thanksgiving cactus. The name Christmas cactus is often restricted to cultivars of the Buckleyi Group. In Europe, plants are mainly sold later in the year, in the period before Christmas, and are usually called Christmas cactus.
Attempts have also been made to classify cultivars by color. A difficulty with this approach is that the flowers of many cultivars exhibit different colors depending on the temperature during bud formation and growth. In particular, temperatures below 57 °F produce pink tones in otherwise white and yellow cultivars, and deepen the color in pink and red cultivars. The availability of iron to the plant has also been suggested to affect flower color.
AN INTERESTING RELATIONSHIP: POLLINATION AND HUMMINGBIRDS
Although this relationship isn’t important to our everyday care of Schlumbergera, it’s an interesting example of adaptability. The flowers have developed adaptations for pollination by hummingbirds: flowers are tubular in shape with abundant nectar, and colors are towards the red end of the spectrum. Most species require cross-pollination to set seed. An exceptions is S. microsphaerica, a species found at higher altitudes where hummingbirds may be absent or less common. This species propagates vegetatively, that is asexually. Birds open the seeds by banging them against trees where the seeds will take root (epiphytic), or segments from the plant break off and root in the tree.
Schlumbergera grows best in light shade. Full sunlight is beneficial in midwinter, but bright sun during the summer months can make plants look pale and yellow. Members of the Buckleyi Group tend to be more tolerant of high light levels than members of the Truncata Group. Too much light causes stems to take on a reddish coloration; very low light levels will prevent flowering.
Ideal growth occurs at temperatures between 70° and 80° F during the growing season, which is April to September for S. truncata, and March/April to September for S. x buckleyi. Improve humidity by using gravel-filled saucers to place your plants upon and keep this moist.
The holiday cactus is tolerant of dry, slightly under-watered conditions, particularly during its rest period after blooming until spring, but do not let the soil dry out. Most problems arise from over-watering, especially during the dark days of winter. The advice sometimes given to withhold water to produce flower buds has been shown to be incorrect. Keep the soil slightly moist throughout the year; water when the top inch of soil in the container feels dry to the touch. Reduce fertilizing from fall until spring. Fertilize plants monthly from the time new growth starts in late winter or early spring, and throughout the summer, using a soluble fertilizer for houseplants.
Best container growth typically occurs in a well-drained potting medium containing one part potting soil, two parts peat moss, and one part sharp sand or vermiculite. Flower production is best when the plant is kept somewhat pot bound. General poor growth can be a sign of over-potting, i.e., the pot is too large for the plant; they like to be snug in a pot. Repotting is only necessary about once every 2-3 years; choose only a slightly larger container. The potting media must be well-drained with good aeration.
When do you want blooms — for Christmas or Thanksgiving? Count backward eight weeks to determine the autumn date to begin to prepare the plant for reblooming. The secret of good flower bud production involves temperature and dark (thermo-photoperiodic) control.
For best flowering provide: bright daytime light, night temperatures between 55° and 65° F, and long nights. Long nights are defined as 13 hours of continuous darkness each day, starting in the middle of September. Continuous darkness means NO light during the dark period, including lamp light within the home. Cover the plant with a black cloth or place the plant in a totally dark room from 6 p.m. to 7 a.m. each day for 6 to 8 weeks. According to the Chicago Botanic Garden, flower buds will form if ONE of the following conditions is met:
- a cool night temperature between 50 to 55 degrees
- 13 hours of uninterrupted darkness (if the temperature is between 55 and 70 degrees)
- 15 hours of darkness (if the temperature is above 70 degrees)
For S. x buckleyi, even cooler nighttime temperatures are preferable. If indoor temperatures at night can be kept at 45-55 degrees F. (which admittedly can be difficult to do in a home), buds will usually form in autumn without employing the strict 13 hour darkness regimen. When we lived in Chicago, we had a huge S. x buckleyi plant that put on a spectacular blooming display year-after-year. I now realize that it had good indirect light, but more importantly, it was placed in a glassed entryway which was uncomfortably cold for us but perfect for the plant. In that case, the dark period was not met, but the cool temperature was.
The Christmas cactus will remain in flower for four to six weeks, with each flower lasting six to nine days. After the plant has flowered, prune back each stem by pinching off enough sections to achieve a uniform habit. (Use the pinched stems for propagation, described below.) Resume normal watering and fertilization when new growth appears.
If you want to put your plant outdoors in the summer, be sure to keep it in a shaded spot with indirect light, and bring it inside before the temperature falls below 45º. Check carefully for insects and clean off with water.
Schlumbergera can be easily propagated with cuttings of 3-5 segments. Different sources give slightly different rooting recommendations. Some say to plant stem segments in moist vermiculite; others recommend placing the segments in a mix of sand/peat or soil/vermiculite/peat. Many sources recommend letting the segments dry for several days in a cool dry place until a callus is formed; this will help prevent root rot. One source emphasized pinching the segments rather than cutting. I think that there are so many minor variations because people have been successful using many different techniques. I’ve successfully rooted the segments in water and then planted them in potting soil but my research didn’t show this as a recommended method.
PESTS AND DISEASES
Unopened flower buds may drop due to a number of factors, including: an excessive number of buds, a sudden change in temperature or light, or other environmental factors, such as drying out of the growing medium. The major disease is root rot, which can be prevented by avoiding excessive watering. Two significant insect pests are: aphids that feed on young shoots, buds, and flowers; and root mealybugs, which attack below soil level. Other insects include mealybugs (foliar-feeding), soft brown scale, and red spider mites. Stems and roots can be rotted by diseases caused by fungi and similar organisms. Aphids, mealybugs, and other invertebrate pests can spread viruses. Symptoms vary with the species, but a loss of vigor is usual. There is no treatment for virus diseases; it is recommended that infected plants be destroyed. See the article from Penn State Extension on Christmas Cactus Diseases.
There is an interesting Q/A regarding spots on a Christmas cactus and recommended treatment, which was sent to the Extension source, Ask an Expert.
Now that we have mastered the identification and care of Thanksgiving cactus and Christmas cactus, let’s turn our attention to the third, lesser-known holiday cactus, Easter cactus. Originally classified as Hatiora gaertneri, it was reclassified as Schlumbergera gaertneri, although it is sometimes identified as Rhipsalidopsis gaertneri (by the Missouri Botanical Garden, for example). For our purposes, we’ll recognize it as being very similar in appearance to the other two holiday cacti except that its stem segments are rounder at the tips and have soft, brownish bristles. Flowers are 2 inches across and made up of a uniform fringe of 12 to 15 pointed petals that radiate out like a hula dancer’s skirt. Care and requirements are very similar to the other holiday cacti, with a couple of main exceptions: it does well in bright light (rather than in part shade), although not in direct sunlight, and it requires a longer, short-day period, 8-12 weeks, before blooming in late February to early March. Flower tones range from white to red, orange, peach, lavender, and pink.
Although noted as easy-care houseplants, Schlumbergera require some steps for reblooming. Those steps mainly require controlled dark and cooler temperatures for about 8 weeks before bloom anticipated at Thanksgiving or Christmas. Watering requirements must also be monitored, and most problems arise from overwatering. Most of our holiday cacti are S. truncata cultivars, Thanksgiving cactus, which has pointed segments and a range of colorful blooms in red, pink, purple, white, and even yellow. Christmas cactus, S. x buckleyi, has more rounded segments and its flowers are beautiful magenta red to pink. Both cultivars are gorgeous holiday additions, and are enjoyable throughout the year. A third holiday cactus, Easter cactus, will brighten the home in early spring in a range of colors.
“Christmas Cactus Diseases,” Penn State Extension, https://extension.psu.edu/christmas-cactus-diseases
“Care of Specialty Potted Plants,” Virginia Cooperative Extension, ext.pubs.www.vt.edu › dam › pubs_ext_vt_edu › 426-101_pdf
“Spots on My Christmas Cactus,” Extension Ask an Expert, https://ask.extension.org/questions/544980
“Care of Christmas Cactus Important After the Holidays,” Purdue University Extension Service, https://www.purdue.edu/hla/sites/yardandgarden/care-of-christmas-cactus-important-after-holidays/
“Christmas Cactus,” Chicago Botanic Garden, https://www.chicagobotanic.org/plantinfo/christmas_cactus
Schlumbergera, Wikipedia, https://en.wikipedia.org/wiki/Schlumbergera
Christmas Cactus (Schlumbergera), Royal Horticultural Society, https://www.rhs.org.uk/advice/profile?pid=840
Commercial Production of Christmas Cacti, University of Massachusetts Extension, https://ag.umass.edu/greenhouse-floriculture/fact-sheets/commercial-producton-of-holiday-cacti
“Is it a Thanksgiving, Christmas or Easter Cactus?” Iowa State Extension, https://www.extension.iastate.edu/linn/news/it-thanksgiving-christmas-or-easter-cactus
Plant of the Week: Easter Cactus, University of Arkansas Cooperative Extension Service, https://www.uaex.edu/yard-garden/resource-library/plant-week/easter-cactus-4-28-06.aspx
“What Holiday Cacti Do You Have?” Missouri Botanical Garden, https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/blog/articleid/242/what-holiday-cacti-do-you-have.aspx