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Holiday / Christmas Cactus - By Martha Maletta, Horticultural Consultant
It has a reputation for being an easy to grow plant, yet I've seen or heard about some very unhappy specimens over the years. Knowing the native habitat and habits of Christmas cactus...perhaps better called holiday cactus... may help in understanding how to grow it.
Holiday cactus, commercially the cultivars of Schlumbergera truncata, the Thanksgiving cactus, is native to Brazil. It is an epiphytic cactus, living on tree branches or in shady stony areas where organic debris accumulates. Rainfall in the region varies from 3 to 17 inches per month; temperatures are fairly constant 60 to 70 degrees F.
The fact that this plant is an epiphyte means that growing it as a house plant requires media that both holds moisture and drains extremely well. For a portion of the season in its natural habitat, conditions are quite moist. In the home, regular watering and high humidity are important. I suspect that one of two situations accounts for most problems with holiday cactus: too much water; too little water.
This plant is a cactus but clearly not an arid habitat species, so it will not be happy treated like a desert cactus. Except for the time just before and during fall when flower buds are being initiated, this plant should only be allowed to dry slightly between waterings. The planting mix should contain more organic material than would be typical for an arid species cactus. The Cornell epiphytic plant mix contains equal volumes of sphagnum peat moss, fir bark (1/8-1/4 inch) and perlite along with lime and fertilizer. Another combines two parts peat moss with one part potting soil and one part perlite. Both the container and mix must drain very well, and the pot must never stand in water. This plant has zero tolerance for wet feet.
Other likely causes of holiday cactus problems relate to light and to fertility. In its native home this plant lives among tree branches. As a house plant in this area, it can tolerate full sun during late fall and winter but needs protection from full sun during summer. If plants are summered outdoors, they will feel right at home under a tree. Because an epiphyteís roots are different from those of terrestrial plants, frequent light fertilization during active growth in spring and summer is needed. The plant grows best at 65 to 70 degrees F but tolerates 65 to 90 degrees F day temperatures.
What about bloom? Holiday cactus is a short day plant; flower buds are initiated by at least 12 hours of uninterrupted dark. But temperature also affects flower initiation; with temperatures in the 50's, night length doesn't matter. Commercial growers can time bloom for the holidays by manipulating temperature and night length. If bloom time is not critical, those of us living in the northern US can let the plants flower naturally between late October to early December. Keep in mind that artificial light can interfere with the process, so place the cactus in a room that is not used much at night.
One to two months before and during fall flower bud initiation (late summer and early fall) reduce or stop fertilizing and cut back on watering somewhat. But do not let the plant dry excessively since this can interfere with flower production. After the flower buds are visible, resume normal watering. One practice used by commercial growers to increase flower display is to remove any stem segments (phylloclades) that are less than 3/8 inch long before short day treatments because they will not produce flower buds. To avoid flower buds dropping before they open, avoid temperature fluctuations, low humidity, drafts and changing the plant's location.
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