You may be aware of the Poinsettia’s interesting Central American heritage. Another tropical that has found its way into the American holiday scene is the Christmas cactus. Like the poinsettia, the Christmas cactus is a short day bloomer. This means that decreasing day length is the trigger for the flowering period to begin. The ancestors of our modern Christmas cacti are native to the forests and jungles of South America. Although a true cactus, the Christmas cactus seems to break all the rules of cactus culture.
In its native environment the Christmas cactus (Zygocactus truncatus, or Schlumbergera bridgesii) and its relatives, the Thanksgiving cactus (Schlumbergera truncatus, or Zygocactus truncatus) and Easter cactus (Rhipsalidopsis gaertneri) are all epiphytes. In other words, these are cacti that grow in trees! These forest or jungle cacti grow their roots into the bark of their host tree. Their only access to moisture and nutrients is from rain and droppings that fall from above. When we think of cacti, we automatically think of the desert and bright sunlight. These forest cacti always grow under a canopy of trees and are never exposed to the full sun of the desert. The environment that these cacti have adapted to is that of the warm, humid jungle with sunlight filtered through the canopy of the forest. The adaptation of the Christmas cactus and its tropical cousins make it an excellent candidate for use as a houseplant. Its habit of flowering just before the winter solstice make it a natural for display during the holiday season.
Like the Poinsettia, it takes very little effort to get your Christmas cactus to flower at the right time. Remember that the shortening days of September and October are what trigger the flowering cycle. The only way to stop the flowering cycle is by exposing the plant to too much artificial light in the evening after the sun has gone down. During the flowering cycle, keep your Christmas cactus moist (but not soggy). After the blossoms have fallen off you should back off on the water for a couple of months. If it needs repotting, this is the time to do it. Christmas cacti won’t want a normal cactus soil (sandy) but will prefer to be in a soil containing sphagnum. This type of soil would normally be used for orchids, bromeliads or other epiphytic plants. As the days lengthen in early spring, you will want to start light feedings. When nighttime temperatures remain above 50 degrees, you could move your Christmas cactus out for the summer.
Remember, this is a forest cactus and so will not want to be placed in a very sunny location. Mine spends the summer hanging in an enclosed porch on the northwest side of the house. This location never gets any direct sun except late in the afternoon and even this is blocked by a large lilac planted on the west side of the porch. My Christmas cactus grows like a weed all summer long. During August, I stop feeding it and during September I will start keeping it drier as well. This will prepare the plant to respond properly to the shortening days with the best possible display of beautiful salmon colored flowers. Since my porch is enclosed, I can leave it in natural light well into October. You will want to leave yours outside as long as possible to insure a response to the approaching solstice. This may involve bringing it in on cold nights and returning it outside the following day. If you must keep it indoors, make sure it is in a room that will be totally dark after the sun goes down. Like the poinsettia, incidental light from a reading lamp can be enough to keep the Christmas cactus from flowering.
The Christmas cactus is very easy to grow. The one I have now started from small 4″ potted specimen a few years ago. Now it is in an 8″ basket and as I write is starting to flower with over a hundred buds yet to open. Very easy color. These forest cacti tend to be long lived. I remember one that grew in the window of a barber shop in Chatham, NY that was huge and had apparently been in the family for over a hundred years! A living heirloom.