|Thanksgiving cactus (Photo by Katie DiCristina)|
There are few and precious blooms around Fairbanks this time of year. Right now, you might find Schlumbergera blooming in your home or office. There are several blooming in the UAF SNRAS/AFES horticulture greenhouse.
I have long called the different species of Schlumbergera, Christmas cacti; but, as I read more about them, I have learned not all Christmas cacti are the same.
Native to rain forests of southern Brazil, Schlumbergera are epiphytic or epilithic, meaning they grow on trees or on rocks. They gather nutrients and water from accumulated vegetative debris that collects in these spaces. There are six recognized species of Schlumbergera, all of which are rare or endangered in their native range.
Schlumbergera are named in honor of Frederic Schlumberger who was well known for his collection of Cactaceae.
How to distinguish between holiday cacti
The species that we most often encounter in homes and offices and are for sale commercially are Schlumbergera truncata and Schlumbergera x buckleyi, a hybrid of S. russelliana and S. truncata. The former is considered a Thanksgiving cactus and the latter the Christmas cactus. Less common is an entirely different genus, Rhipsalidopsis gaertners and is called the Easter cactus. Common names are broadly based on blooming season, but there are other differnces between the species. Floral and leaf morphology can be used to distinguish between species. Flowers of Christmas cactus are radially symmetrical or actinomorphic; whereas, Thanksgiving cacti are radially aymmentrical or zygomorphic. The stem segments of Thanksgiving cactus have two to four pointed serrations along the margins. The Christmas cactus has rounded serrations. The color of anthers differs between the species. Thanksgiving are yellow and Christmas are purple-brown.
Photoperiodism and flower induction
Photoperiodism is the physiological reaction that living organisms have to length of day or night. In the case of plants, certain developmental stages are triggered by the period of uninterrupted darkness they experience. Increasing night length induces flower bud production in Schlumbergera. The following conditions will help your Schlumbergera to flower:
Temperature: 60-68 day. 55-65 F night.
Light: Bright, direct light during the day.
Photoperiod: 13+ hours of uninterrupted darkness each day for eight weeks.
Pruning: Before buds form, pinch back terminal stem segments that are less than 0.4” long. Pinch back stems again in early June to stimulate branching and increase the quantity of terminal ends for future flower buds.
Media: Well draining, slightly acidic (pH 5.5-6.2).
Water: Water when dry to touch.
Light: Part shade (different than for flower induction time of year).
S. bridgisii (Lem.) Loefgr
S. kautskyi (Horobin & McMillan) N.P. Taylor
S. obtusangula (K. Schum.) D.R. Hunt
S. opuntioides (Loefgr. & Dusen) D.R. Hunt
S. russelianum (Hook.) Britton & Rose
S. truncata (Haw.) Moran
Katie DiCristina is a research technician at the Georgeson Botanical Garden, a program of SNRAS.