By Claire Woodward, Ph.D
FOC Gift Shop Director
Holiday Cacti, Schlumbergera, Cactaceae
Holiday cacti are now adding a little spice to the displays in the Fern House. These popular houseplants are sold under the common names Thanksgiving and Christmas Cacti. The two names are not part of cunning marketing strategy, but they are in fact two distinct species. Thanksgiving Cacti (Schlumbergera truncata) flower in November and Christmas Cacti (Schlumbergera russelliana) flower in December. Unfortunately both can be found being sold as Christmas Cactus.
These cacti come from the coastal mountains of South East Brazil. S.truncata grows in the moist forests at elevations between 3000-5000 ft and S.russeliana grows at higher elevations in the cooler, dryer forests. They are collectively referred to as Leaf or Jungle Cacti. Schlumbergera are epiphytic, growing in the nooks of tree branches and rocks, getting nutrients and water from the air and rain. They both have flattened, leafless, photosynthesizing stems called phylloclades. S.truncata has 2-4 teeth (dentate) at the ends of truncated phylloclades, the flowers are asymmetrical, the anthers are yellow and the ovaries are cylindrical and straight. S.russeliana in contrast has rounded ends to the phylloclades, with rounded teeth (crenate), radially symmetric flowers, angled ovaries, and purple anthers. In the 1840’s Mr W.Buckley of Rollinson Nurseries, UK, produced hybrids between S.russeliana and S.truncata, known as the Buckleyi type which have a mix of the two species characteristics, but tend to bloom in December and are also referred to as Christmas Cactus.
Whatever you decide to call them, Holiday cacti require bright indirect light and well draining potting soil. The requirements for producing a showy floral display are relatively easy in the Pacific Northwest. They are stimulated to flower by short days, a photoperiodic response, that is modified by temperature. To get your holiday cactus to flower, in September you need to restrict the hours of light to 8-10 hours a day and keep them in a room at 60-68°F. Which luckily (or not) for us begins to happen naturally. The plants can be placed in a cooler room that is not given extra light during the evening as this may be enough to disrupt the bud set or outside in a shady position and brought inside when temperatures dip below 50°F. At the same time as light is reduced, no fertilizer should be given to the plants and watering should be reduced to allow the plants to become drier between watering. Once the tiny buds appear at the tips of the phylloclades begin to water more frequently. Over watering, like with all cacti, is the easiest way to kill these plants. By making sure the soil is moist but never wet will ensure the plants thrive from year to year blooming in time for the holidays.