While most cacti are very heat and drought tolerant, Christmas cacti are a little different. They are more like tropical plants than desert plants, so they're not as drought tolerant as the typical cactus. They also keep their beautiful blooms much longer in cooler temperatures. Many gardeners enjoy the challenge of keeping their Christmas cactus healthy throughout the year so they can enjoy their blossoms each Christmas season. This is harder than most would think, but with proper watering and maintenance it's entirely possible to enjoy your Christmas cactus for many Christmases.
Monitor the Soil
There are not strict guidelines as to how often you should water your cactus. Instead, monitor the plant to determine when watering is necessary. According to Purdue University Extension's newsletter, you should, "water thoroughly when the top inch or so of soil feels dry to the touch." You may also notice the plant beginning to wilt if it goes too long without water. Purdue's Extension Service also notes that, "the length of time between waterings will vary with the air temperature, amount of light, rate of growth and relative humidity."
If your cactus dries out often or the flowers seem to wilt frequently, you may need to transplant it into a bigger container, rather than continually water it. To survive and thrive, Christmas cacti must have soil that drains easily. Purdue's newsletter recommends either purchasing potting soil mix for succulents or making your own by, "combining two parts plain potting soil with one part clean sand or vermiculite."
Provide Correct Environment
While properly watering your Christmas cactus is important, it's also important for it to live in the correct environment. For example, keep it away from drafts from fireplaces and heat vents, and place it in a well-lit location. These two things are particularly important if you want your cactus to bloom. Extreme temperature change or drafts can make flower buds fall off the plant before they've even had a chance to open.
In addition to proper watering, to further the likelihood that your Christmas cactus survives throughout the year, you should periodically fertilize it. Purdue's Extension Service recommends to simply use a fertilizer made for blooming houseplants and to follow the directions on the label for how and when to apply it. There is no need to fertilize the plant while it's in bloom.