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What's Blooming: Holiday Cacti

 

Christmas cactus (Schlumbergera x bridgesii

What's Blooming:  Holiday Cacti
by Bryan Fischer, Horticulturist, 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 the homes of family and friends, yet how poorly understood they are, both in identification and in care requirements. This post 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.  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.

Thanksgiving cactus (Schlumbergera truncata)

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. 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, with cooler nights (60 – 65 degrees Fahrenheit) encouraging the process.  Without both the chilling and long-night requirements being met, holiday cacti will fail to bloom.

If your cactus fails to bloom in early winter and doesn’t quite match the descriptions above, it’s possible that you are actually growing an Easter cactus.

Distinguished most easily from winter-blooming relatives by their spring display, Easter cacti also provide a few other clues to aid in identification. Smaller in overall size when compared to their peers, these attractive plants have a more upright, arching form and blooms with a radial symmetry, rather than the bilateral symmetry employed by Thanksgiving and Christmas cacti. The flowers produced by Easter cacti also considerably flatter than other holiday cacti, which typically have a distinct, tubelike shape before the face of their blooms.

In opposition to the pointed leaf edges of Thanksgiving cacti, Easter cacti have the smoothest, most rounded leaf edges of the commonly seen holiday cacti. Most helpful to me, the tops of leaf segments are also tipped with tufts of very short “glochids” that appear like hairs to the naked eye.

Easter cactus (Schlumbergera / Rhipsalidopsis gaertneri)

I prefer the refined, star-shaped blooms of Easter cacti to their gaudier counterparts. In whites, pinks, oranges and reds, they make excellent focal points in our homes at a time when it is so easy to appreciate the merits of a vibrant floral display. Each bloom is surprisingly long lived, closing each night and reopening each morning, with some plants blooming for weeks or more.

Occasionally, Easter cacti bloom without any conscious effort on our part. Don’t bank on this, however. To ensure bud set – and thus bloom – ensure that your Easter cactus receives the same winter treatment as your other holiday cacti, with long nights of uninterrupted darkness and cooler temperatures than it gets during the summer. Easter cacti respond well to cooler temperatures than other holiday cacti – down to 55 degrees Fahrenheit – but only for a brief period. Grow your Easter cactus in a manner identical to your other holiday cacti, with a slight chilling through fall and early winter, before subjecting the cactus to a cooler chilling (ideally 55 – 60 degrees) for four to six weeks to initiate bud production. This period of cooler chilling must also align with long nights, and so will be effective if started around the first of the year. This cooling requirement can often be achieved by placing the plant in a cool window or heated garage. Bud set should begin during or just after this period.

While plants are chilled, it’s wise to water a bit more sparingly than one might otherwise. Not only does it reduce odds of rot taking hold while the plant’s water needs are reduced, but it also strengthens the cue for these cacti that it is time to set buds.

Forcing buds on all holiday cacti:

·       Sustain the three conditions below for at least four weeks simultaneously:

o   60 – 70 degrees Fahrenheit  

§  60 – 65 degrees at night is best

o   14 hours of uninterrupted darkness essential to set buds

§  Naturally mid-November in Northern Colorado

§  Can force this process by covering plant / excluding light

Forcing buds on Easter cacti:

·       Bud set occurs a couple of months later

·       Relies on the steps above for holiday cacti, plus:

o   A sustained (four week) drop in temp to 55 – 60 degrees after the above requirements are met – consider placing plants near your coolest window

o   Continued uninterrupted long nights (14+ hours) through the chilling period

o   Drier than average soil – reduce watering to just enough to prevent leaf shriveling

·       Return to room temperature by mid-February; buds should be set and long nights no longer required; return to standard watering

 

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