Thanksgiving cactus (Schlumbergera truncata) and Christmas ceactus (Schlumbergera bridgesil) are very popular fall and winter flowering houseplants. These cacti are native to Brazil and come in a wide variety of colors such as red, purple, lavender, peach, orange, cream, and white. The Schlumbergera species are epiphytes that grow in tree branches in shady rain forests.
Thanksgiving cacti normally flower around Thanksgiving, about a month before Christmas cacti bloom. Flowering can last seven to eight weeks if the plants are kept at 68F. Thanksgiving and Christmas cacti looks similar, but can be identified by looking at the shape of the flattened stem segments called phylloclades. The Thanksgiving cactus phylloclades, or stem segments, have two to four saw-toothed serrations or projects along the margins. The stem margins on the Christmas cactus are more rounded. Photosynthesis occurs within the green phylloclades since the holiday cacti do not have any true leaves.
The holiday cacti grow best in light shade. Full sunlight is beneficial during fall and winter, but during the summer months the bright sun can make the plants look pale and yellow. During growing season, between April and September, the ideal temperatures are between 70 and 80F. During the fall the cacti depend on shorter day lengths and cooler temperatures to set their flower buds. Do not allow the temperature to rise above 90F or drop below 50F. Hot temperatures can cause the flower buds to drop. Long nights are essential for the flower buds to set. Fourteen hour or more of continuous darkness each day should start around the middle of September and continue for at least six weeks. Pinching back the stem in early June helps to promote branching and more terminals for more flowers.
The holiday cacti are tolerant of dry, slightly under-watered conditions during the spring and summer. Be careful not to over water during this time. Only water when the growing medium is dry to the touch. During the fall, the growing medium needs to be kept moist to prevent flower bud abscission. However, do not let water stand in the saucers beneath the pot.
Fertilize holiday cacti monthly in late winter to early spring. Holiday cacti have a higher requirement for magnesium than many plants. You can use Epsom salts (magnesium sulfate) monthly are a rate of 1 teaspoon per gallon of water, but do not apply the same week as the regular fertilizer. Stop feralization during the late summer for greater flower bud production in the fall.
Holiday cacti are easy to propagate by cuttings in May or June. Pinch off sections of stems with three to five phylloclades. Allow the ends to callus by placing them outdoors in the shade for a day or two. In four-inch containers place three cuttings about once inch deep into the potting soil or use five cuttings in a six-inch container. Water the soil well and cover the plants with a clean plastic bag secured with a rubber band around the container. The plastic bag will act as a miniature greenhouse to keep the relative humidity at 100% to enhance rooting. Place the container in bright, indirect light until the roots have formed in three to eight weeks. The plastic bag can then be removed.
For more information on Thanksgiving and Christmas Cacti, please visit the HGIC website at hgic.clemson.edu. Tune in on Tuesday nights to watch “Making it Grow” at 7 p.m. on SCETV or mig.org. Email Outen at callenb@clemson.edu.
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