Plant of the Week
Holiday Cactus, Christmas Cactus,
Thanksgiving Cactus
Latin:
Schlumbergera truncata
Cacti have always fascinated me. Most gardeners aren’t so
fascinated. In fact, many turn downright belligerent when you even bring up
these spiny little creatures. But even the most ardent cactus-hater surely
must delight when the delicate flowers of the Thanksgiving cactus appear in
early fall.
You might think that the Thanksgiving cactus would come from the desert
areas of the New World, but it actually inhabits the tree tops of southern
Brazil, sharing its space with orchids and bromeliads.
Thanksgiving cactus is a true cactus, but it lacks the spines and the
round, chubby little body normally associated with members of their plant
family. It produces flat, segmented leaf-like branches called cladophylls.
The branches are edged with long, serrated teeth.
The showy multi-petaled flowers come in shades of pink, rose, red, white
and even yellow. They appear from mid-November until after Christmas.
This group of flowering cacti was originally hybridized by William
Buckley in Rio de Janeiro about 1840. The genus was named after a Belgian
horticulturist, Frederick Schlumberger. Schlumbergera are hybrids and
have slightly different blooming times. If a particular plant blooms in
November, it’s a ‘Thanksgiving’ cactus. If it blooms around the end of the
year, it becomes a ‘Christmas’ cactus, even though it is not the true
Christmas cactus.
The true Christmas cactus, Schlumbergera x buckleyi, differs from
S. truncata. The S. Truncata has an asymmetrical flower and wings on
its ovary.
The common names associated with American holidays, or even Christian
holidays, have limited meaning to the rest of the world. In Europe, this cactus
is called ‘Crab cactus.’ The Europeans have never caught on to the turkey and
cranberry idea. In its native Brazil, even ‘Christmas cactus’ is meaningless
because the plants flower during April and May, the normal fall season of the
Southern Hemisphere.
The initiation of flower buds on the Thanksgiving cactus is triggered by
both temperature and day length, i.e., short days of fall. If the
temperature is lower than 60 degrees, plants set flower buds regardless of
the length of the day or night. If the temperature is more moderate, plants
show a classic short-day response. They initiate blooms as the days get
shorter in the fall.
Thanksgiving cactus has a 12-hour critical night length, meaning if it
receives more than 12 hours of light in a day, it will not bloom. The vernal
equinox occurs on Sept. 21, so all days after that date have less than 12
hours of light, which triggers trigger flowering. Plants also respond to the
cooler days. After exposure to either cool temperatures or short days for
six weeks, flower buds will appear.
One of the recommendations often found in older books discussing this
species is the practice of giving a "dry-down" treatment in the early fall
to encourage good bloom set. A number of researchers have looked at this
practice and found it actually decreases bloom numbers. On average, the
number of blooms per cladophyll was 2.5 for plants kept uniformly moist and
1.5 for plants exposed to a dry-down treatment.
The Thanksgiving cactus should have a good, well-drained potting media.
It’s best kept somewhat confined, so only transplant the plants to a larger
pot about every other year. As the blooms develop, give the plant a good
sunny window and keep it uniformly moist. In the summer, move the pot to the
patio and put it where it has a bit of shade during the hottest part of the
day.
By: Gerald Klingaman, retired
Extension Horticulturist
- Ornamentals
Extension News -
October 20, 2000
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