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Nothing symbolizes the holiday season to a horticulturalist like a holiday cactus in full bloom.  These fascinating plants are cacti, but not at all like the full-sun, desert loving specimens we commonly think of.  Instead, these plants hail from the treetops of forests in Brazil, which is quite different than the desert ecosystems associated with other species of cacti.  They are all epiphytes, living in mostly shaded tree tops and rooting into pockets of organic debris instead of soil.

There are three species of commonly available holiday cacti: the Thanksgiving cactus (Schlumbergera truncate), the Christmas cactus (Schlumbergera bridgesii) and the Easter cactus (Hatiora gaertneri).  All three of these plants were named according to their bloom time, with natural flowering in the wild coinciding with their respective holidays.  Of the three, Thanksgiving cactus is, by far, the most commercially available species.  I have found it to be much easier to care for than its festive cousins, with Easter cactus being the most difficult to keep in optimal health and flowering. 

Both Thanksgiving cactus and Christmas cactus are short-day plants, meaning they flower when days become shorter in length (8-10 hours) and nights are longer (12- 14 hours).  Flowering can also be influenced by temperature, so exposure to cooler temps (especially at night) will induce blooms.  For these reasons, holiday cacti are pretty easily manipulated and the horticulture industry is very good at controlling environmental conditions to ensure flowering occurs at the optimal time for marketing and sales purposes.  Often times, Thanksgiving cactus is sold this time of year with the label of ‘Christmas cactus’ since these plants were exposed to optimal temperature and light to ensure that flowering will occur between now and Christmas time. 

Many times, the ‘Christmas cactus’ we purchased last year just doesn’t flower well the next year.  Sometimes flowering in subsequent years is sporadic and may randomly start at the wrong time of year or may not occur at all.  All of these issues are related to the light and temperature your plant has been exposed to, which may have confused its timing.  To achieve optimal flowering at the desired holiday, you will need to reduce light exposure and the overnight temperatures about 4 weeks before the holidays.

Light exposure can be managed by covering your plant with paper bag or putting it in a closet for about 12-14 hours a night to achieve the required dark period.  The easiest way to accomplish this is to block light from about 6pm to 8am every evening.  Just don’t forget to pull your plant out during the daytime so it can receive the light that is needed as well.  Additionally, as little as a couple of hours of artificial light exposure during the dark period can negate all your efforts, so be wary of even the dimmest artificial lights during nighttime.

After about 3 or 4 weeks, you should start to see flower buds forming which indicates you can go back to normal lighting, but it is important to keep plants cool at night.  Flowering will not occur if nighttime temperatures are over 68⁰F. 

Temperature may actually have a greater influence on plant response and flowering.  Plants exposed to continuously cool temperatures (50-60⁰F) in September and October will often produce flowers regardless of day length or light exposure.  An unheated porch or cooler part of your home may provide appropriate temperature exposure if our weather is consistent enough.  Many folks move their cacti outside for the growing season, which can also naturally expose them to the cooler temperatures.  Take care to bring your plants in if temperatures drop too much below 50.  It is also important to find an outdoor spot with partial sun. Remember, these plants naturally occur in shady tree tops, so they cannot handle full sun or exposure to temperature extremes.

Over the years, I have really enjoyed the holiday cacti although I cannot say they always bloom as expected, usually because I failed to provide the right environmental conditions.  Nonetheless, that doesn’t bother me because, even without a wonderful holiday display of blooms, these plants are interesting succulents that add to any house plant collection. To me, the real fun comes from experimentation and the always-difficult task of trying to mimic nature in an indoor environment.