Bryan Fischer | Gardens on Spring Creek
Holiday cacti have intrigued me since I was a kid. Particularly, I’ve been fascinated to see how common they are in homes of family and friends, yet how poorly-understood they are, both in identification and in care requirements. This article seeks to demystify these ubiquitous, durable and exceptionally long-lived houseplants, for our benefit and theirs alike.
While they are true cacti (family Cactaceae), the plants we call holiday cacti today did not originate in the desert as many would expect. Rather, they grow as epiphytes in tropical and subtropical South American rainforests, meaning they live on the bark of a host tree. However, they differ from parasites in that they glean no nutrition from the trees upon which they grow. As a result of their origins, all holiday cacti perform well in homes with indirect light, temperatures above freezing and medium to medium-dry soil.
Three main types of holiday cacti exist in the horticultural trade, recognized most often by the common names of: Christmas cacti (Schlumbergera x bridgesii), Thanksgiving cacti (Schlumbergera truncata) and Easter cacti (Schlumbergera / Rhipsalidopsis gaertneri). Each with a slightly different set of care requirements, understanding which type of plant you are growing can make a significant difference in the performance of your holiday cactus. All bloom in response to night length and temperature, but at different thresholds.
Perhaps the most easily distinguished from its peers when out of bloom, Thanksgiving cactus is unique in that its leaf edges have pointed teeth, rather than rounded or scalloped ones. When these cacti do flower, it will typically be between November and January, with flowers that generally turn to face outwards from the plant. Christmas cactus, the most similar in appearance to Thanksgiving cacti when in bloom, have scalloped leaf edges rather than pointed leaf edges, and typically have flowers that face down more than they face outwards.
Regardless of exactly which of the two you may be growing, they both initiate bud formation once nights are 14 hours or longer – about the second week of November in Northern Colorado. Many indoor lights can affect this process, so consider moving your cactus into a room that will remain dark between sunset and sunrise for this period. Temperatures also influence bud formation in these cacti. Cooler nights (60 – 65 degrees Fahrenheit) will encourage this process. Without both the chilling and long-night requirements being met, holiday cacti will fail to bloom.
If your cactus has leaves shaped like those of a Christmas cactus but with small, stiff hair at leaf tips, it’s possible you have an Easter cactus. If this is the case, the plant will also fail to bloom in early winter, as it is waiting for an additional chilling cue before setting buds. Don’t worry; the care requirements for the species are the same until early January when you can watch for a follow-up article discussing forcing buds on Easter cacti.
To force buds on Thanksgiving and Christmas cacti, sustain the three conditions below for at least four weeks simultaneously:
- 60 – 70 degrees, with 60 – 65 degrees at night best
- 14 hours of uninterrupted darkness are essential to set buds. This occurs naturally in mid-November in Northern Colorado. You can force this process by covering the plant / excluding light
- Don’t overwater