The Christmas cactus, Schlumbergera x buckleyi, a hybrid between S. russelliana and S. truncata and sometimes listed as Schlumbergera bridgesii is a common holiday plant. It is a native of the coastal mountain forest of southern Brazil where it grows as an epiphyte on forest trees or moss-covered rocks. This native environment is relatively cool, shaded by clouds or forest canopy, and high in humidity. Although not the environmental parameters we associate with cactus, this is a true cactus.
It is a stem cactus, having no typical leaves, only flat stems. Stem cactus varieties have areoles located on the distal end of each stem section. Areoles are special structures that resemble tiny pin cushions of wool and bristles and are the location where flowers arise. Plant breeders have developed varieties with flowers ranging from white to purple. In its native habitat, the Christmas cactus produces red, tubular flowers with abundant nectar, all characteristics that favor pollination by hummingbirds. Fruit and seed set require cross-pollination. This is a reason we have little or no fruit set in Hawaii.
As is the nature of gardeners, we love plant challenges and getting a Christmas cactus to rebloom is a challenge not to be passed up. Once the flowers have died away, the first decision may be to repot your cactus or plant it in a more natural setting. When selecting a potting medium, choose one that drains well. Purchase a commercially available succulent media or mix your own using perlite or cinder mixed with peat moss or coir. Christmas cactus is known to do well on tree fern trunks. Fertilize with a blooming plant fertilizer according to label directions. In outdoor locations, place plants in a semi-shady spot since too much light may cause the development of red pigment in the stems. When grown indoors, place in a well-lit location for good flowering. Christmas cactus grown under low light may not flower. Although it is a true cactus, the Christmas cactus does not thrive in extremely hot or dry environments. It thrives in a moist, cool, tropical environment and does well in Hilo.
Propagation is easy to accomplish by planting stem segments. After the bloom period, prune the cactus. This will result in a bushier plant and provide you with many cuttings for propagation. Place each cutting in moist potting medium to a depth of one segment. Keep cuttings in a cool, shady location for three weeks or until roots start to develop. Keep soil moist but not wet. Once roots develop, move plants to a sunnier location.
Flowering can be initiated by two environmental triggers: day length and cool temperatures. When days are shorter than 12 hours, bud formation is initiated and the plant should bloom in six to eight weeks. Avoid house or street lights to ensure good blossom production and keep it away from excessive heat sources.
If your plant doesn’t bloom, it might not be a Christmas cactus. Blooming stem cactus is commonly called Christmas cactus, but might in fact be Thanksgiving cactus, Schlumbergera truncata, or Easter cactus, Rhipsalidopsis gaetneri, which look very similar to the Christmas cactus. The Christmas cactus has a scalloped stem section with no points and flowers are borne on the tip section and are pendent. Also, the branches are arcing and pendent in appearance. They bloom naturally in November and December and possibly between March and May, as well. Thanksgiving cactus has pointed teeth along the stem edge. Flowers protrude horizontally from stem tip. The Easter cactus has rounded teeth along the stem edge, tiny bristles on the tip of the end segment and typically blooms only once in the spring. This plant species also has the characteristic of shedding its stem sections when water-stressed.
Whichever stem cactus you have growing, with the proper care it will give you years of beautiful blossoms.
For more information on this and other gardening topics, visit ctahr.hawaii.edu/Site/Info.aspx or visit any Cooperative Extension Service office.
Russell Nagata is the Hawaii County administrator of the University of Hawaii at Manoa College of Tropical Agriculture and Human Resources. He can be reached at firstname.lastname@example.org.