 |
| 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