By Julie Barnes
Christmas cacti are spectacular holiday plants brandishing lush pendulous flowers in an astonishing array of common Thanksgiving cactus, Schlumbergera truncata and the rare hybrid Christmas cactus, Schlumbergera bridgesii, cross bred from the Thanksgiving cactus. The true Christmas cactus, Schlumbergera bridgesii, blooms later and does not exhibit the same kaleidoscope of colors or variations seen in the vigorous growing Thanksgiving cactus. These attributes make it less profitable for holiday plant sales. For this reason the Thanksgiving cactus is sold as the "Christmas cactus." If you want to possess a true Christmas cactus you literally have to acquire this exceptional beauty from someone who has one where its stem segments can be easily rooted. Otherwise it is not available in stores.
The name "cactus" brings to mind desert conditions and can be quite misleading to some. Besides desert cacti, the cactus family also contains jungle cacti which grow in rainforests. These winter flowering houseplants are native to Brazil's moist rain forests resting on trees as epiphytes. An epiphyte grows on another plant for support and does not take nourishment as a parasite would from a host plant.
Schlumbergera flourish in plant debris trapped among the tree branches maturing rapidly in the rainy season. When the dry season returns they become dormant subsisting on water stored in their flattened leaf like stem segments. These plants will deteriorate if treated like desert cacti. Schlumbergera thrive in conditions similar to their native location: porous potting mix, high humidity, with partial shade in spring and summer. They also bloom best when pot bound. Repotting should only be necessary every three years.
Thanksgiving and Christmas cactus differ mainly in the shape of their leaf like stem segments. Thanksgiving cactus, Schlumbergera truncata, or Zygocactus, Claw or Crab cactus blooms several weeks before the Christmas cactus. It has stem segments with strongly toothed or pointed edges that make them appear claw-like. Its growth habit seems to be more upright.
Christmas cactus, Sclumbergera 'bridgesii', blooms later. It has smaller smooth stem segments that are scalloped along the edges. Its growth habit tends to more pendulous or drooping. Schlumbergera are short day plants similar to poinsettias or mums forming buds as day length becomes shorter than 12 hours. They also need a "chilling requirement" to initiate flower formation by subjecting them to autumn temperatures below 550 F. To achieve this: Relocate the plant to a shady location outdoors in the summer keeping the potting media consistently moist, then, in autumn only dampen the plant enough to prevent it from wilting. Move it back indoors before temperatures drop below 450 F into a low light location and withhold water in order to encourage re-blooming. After buds form and become quite noticeable, shift the plant back into the light and water, preferably, in a sunny location with minimal temperature fluctuations while allowing the soil to dry slightly before watering. If flower buds start to drop, overwatering, exposure to cold drafts, being too close to a heat source such as a vent or fireplace, or low humidity can be the cause. After it is done blooming, this plant should only be watered when the media becomes dry. Holiday cacti are long lived plants that are often handed down from generation to generation. With proper care their dramatic blooms can be a striking part of the holiday season.