Many small cacti generally referred to as Christmas cactus show up on retail shelves at this time of year. Depending on the particular variety and flowering time, they may also bear the name of Thanksgiving cactus. I haven’t seen any with the names of Hanukkah cactus or Kwanzaa cactus just yet, so Holiday cactus could serve as a good umbrella term. Just to keep things simple, I’ll refer to all of the plants in the genus Schlumbergera as Christmas cactus. (The Easter cactus is in the separate but closely related genus Hatiora.) Christmas cactus at one time were placed in the genus Zygocactus, but this term is now taxonomically invalid. Still, you’ll often see it on plant labels, presumably since it rolls off the tongue more easily than Schlumbergera.
Despite what I read in one source, the Christmas cactus and the Easter cactus are indeed true cacti; they just don’t closely resemble some typical members of the cactus family (Cactaceae), such as the prickly pear (Opuntia) or the iconic giant saguaro (Carnegiea gigantea). As is true of most succulents, cacti can store considerable quantities of water. Cacti lack true leaves; instead, they store water and carry on photosynthesis in their greenish stems. In some species, the leaves have evolved to become spines; luckily for those who grow them, the Christmas cacti are not armed.
The somewhat atypical appearance of Christmas cacti among their more spiny relatives presumably derives from their native home in the moist mountains of southern Brazil. In a narrow coastal band some 200-300 miles on either side of Rio de Janeiro, Christmas cacti grow clinging to trees and rocks. Even in the drier tropical winter, clouds and fog keep them supplied with water. But given that they are growing in almost no soil, moisture quickly drains away. Growing at elevations of 2,300’ to 9,000’, they prefer cooler temperatures than plants from the tropical lowlands.
Christmas cactus now come in many colors—pink, yellow, tangerine, and white, as well as the traditional red. Aside from flower color, there are two somewhat different types of plant morphology: most modern cultivars have pointed teeth—not really sharp, however—on their leaves, flowers held nearly horizontal, and yellow pollen. These belong to the Truncata group, for those fond of horticultural nomenclature. The Buckleyi group have rounded symmetrical “teeth,” flowers are pendant, and pollen is pink. This group is also tolerant of higher light levels.
How should Christmas cactus be grown? Some sources describe it as an “easy” plant. Maybe that’s true if you don’t care about it flowering, but I doubt this applies to very many people. So, here’s what I’ve gleaned from my reading, not only about growing your Christmas cactus but getting it to flower year after year as well. And let me emphasize this is what I have read. I bought my Christmas cactus a few days ago, so I don’t speak from personal experience as yet.
First, let’s review the natural conditions that Christmas cactus grows in: the southern edge of the Brazilian tropics, with both wet and drier seasons; mid- to high-elevations with cooler temperatures; partial shade; excellent drainage; and day length varying from 10 ½ to 13 ½ hours. Starting with soil, you could mix your own, adding some sand or perlite to ordinary potting soil. Since I grow a fair amount of succulents, I just buy a bag of soil that is labeled “Cactus and Succulent Mix.” (Of course you’re usually going to buy your Christmas cactus already potted, but at some point you’ll have to repot it.)
Next, provide bright indirect light. If you move your plant outdoors in the summer, be sure it gets shade from late morning to sunset. And given that these plants are not fond of really hot temperatures, I’d consider keeping them in an air-conditioned place for the summer.
For most of the year Christmas cactus should be watered when the top inch of the soil dries out. They do like humidity in the air, and heated houses tend to be dry in the winter. You can add moisture by placing the pot on top of a tray filled with pebbles and water, but be sure to keep the water level below the top of the gravel.
Ideally, temperatures would be around 55-65 degrees at night and 70 during the day. Realistically, unless you have a special space for your plants, you’re probably going to have nighttime temperatures at the upper end of that range. Regardless, keep your Christmas cactus away from radiators, fireplaces or drafts.
Now for the trickier part: getting your Christmas cactus to flower, much of which depends on longer nights. Our nights are twelve hours long by September 21 and continue to get longer afterwards, so that shouldn’t present a problem. Except that your plant will be indoors, presumably with artificial lights going on and off. Plants that require long nights, rather than just short days, don’t want any interruption during the night. Even if your plant’s room goes dark at 5 p.m. and doesn’t light up again until 7 the next morning, it’s “rhythm” will be thrown off if somebody goes into the room at 11 p.m. and flicks on the light. The Christmas cactus will see that as one six-hour night, followed by an eight-hour night. So, “lights out,” should mean lights out until the next morning.
As fall approaches, a Christmas cactus will also need less water. One source recommends cutting back on water radically in October, then increasing water when the buds appear. This same source also showed “14 Easy Steps to Successfully Growing Christmas Cactus.” Frankly, once you go beyond five steps, I don’t think it’s easy anymore.
Let me emphasize my novice status with this plant once again. I’m hoping to hear from someone who will say, “I just leave my Christmas cactus in the same place all year, water it once a week, and it blooms like crazy.”