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The Christmas cactus or Zygocactus truncatus is a true cactus, but its natural home is a forest so it isn't surprising that they have much different requirements than desert cacti. They need a consistent supply of moisture and a fast-draining organic soil mix.
In order to bloom, forest cacti need both a resting period when water and warmth are decreased and a during the summer, it will benefit from being put outdoors. They need bright light but should be kept out of direct sun. Fertilize every two to three weeks with a dilute houseplant fertilizer and watered when the top of the soil begins to dry out during active growth. To ensure bud set for late December bloom, reduce watering and keep the plant where it will receive cool night temperatures (50-55 degrees), and 12-14 hours or darkness per night during November. Once the flower buds set increase water and temperature.
A similar plant, Rhipsalidopsis gaertneri or Thanksgiving cactus is easily confused with a Christmas cactus, and often sold at the same time. The edges of the leaf-like stem segments of the Christmas cactus have pointed projections where the Thanksgiving cactus is more scalloped. Not surprisingly they normally bloom bit earlier, around Thanksgiving. They require the same culture as a Christmas cactus but don't seem to need the long night treatment in order to bloom. Both have spectacular blooms often in vivid pinks and reds, as well as white. Once done flowering both need a resting period where they are kept cool, and watered less frequently.
These delicious winter bloomers can live for decades and keep increasing in beauty and size. While thinking of indoor plants, what about using tap water on them? Many good in-door gardeners recommend that chlorinated tap water be allowed to stand overnight to allow the chlorine to escape as a gas. Some go so far as to collect rainwater or use distilled water on their precious houseplants.
Researchers at a University of Connecticut agricultural experiment station tested a wide range of foliage plants, flowering plants and vegetable seedlings to see if chlorine did damage plants. Ordinary treated tap water contains chlorine at only one part per million or less, the researchers used water ranging in chlorine concentration from 0 ppm to 77 ppm. The test plants were irrigated with this water for a period of twelve weeks. It took quite some time for any of the potted plants to show any negative effects from the treatments, and then only at higher concentrations. The take home message: chlorine from municipal water supplies is not likely to damage any of your houseplants, bedding plants or vegetable transplants.
Fluoride, which is often added to municipal water supplies to reduce tooth decay, does have an adverse effect on many commonly grown houseplants. Fluoridated water causes sensitive plants like palms, dracaenas, spider plants and others to have brown, dead leaf tips and edges. Scientific tests done in Florida, where houseplants are grown commercially, suggest that even fluoride naturally present in some ground water can damage highly sensitive plants. Fluoride will not go off as a gas even if the water is allowed to stand overnight. Rain and distilled water are options to think about for very sensitive plants. You can also trim off the ugly bits with a sharp scissors. If you follow the natural shape of the leaf it will be almost unnoticeable, and certainly look better than the brown leaf tips.
There is an advantage to allowing the water to come to room temperature, unheated tap water can be as chilly as 45F during the winter. Think of it this way, if you were looking out the window minding you own business and someone threw a bucket of icy cold water in your lap, how would you react? In addition to the temporary shock, it's even possible that the consistent use of very cold water on tropical plants could cause the death of enough root hairs to affect plant growth. Use room temperature water, and keep in mind that during the winter, for most houseplants, growth slows down the plant doesn't use as much water. Check once a week and only water as needed, perhaps twice a month or even less for plants like clivia and jade plant. They need to stay completely dry for December and January.
Hortsense: Managing plant problems with Integrated Pest Management
