Having trouble getting your Christmas cactus to bloom on schedule?
Looking at a plant’s origins often gives valuable clues on its cultural needs. Christmas cactus, Zygocactus truncatus, is a native of the mountains of Brazil where it lives in semi shade as an understory plant in the rain forest. It wants some sun and appreciates the cool nights that come from its mountain habitat, with well-drained soil that dries out just a bit between rainfalls.
For best results as a houseplant, give this cactus the same treatment as it would get in nature. That means you can put it outdoors in dappled shade during the warm months, or grow it indoors it in similar bright conditions. It will not be happy if it is too wet, too dry, or too dark. But it will burn in too much afternoon sun.
To induce blooming, both cool nights and day length can be important. Simply leaving the plant outdoors until night temperatures get below 50 degrees usually works well. The length of darkness is not as important as the temperature. But if you cannot provide the cool night temperatures, the long night environment will also induce flowering. So, like the poinsettia, put it in a room where no one turns on a light at night until the buds start to form.
Like most flowering plants, these cacti will hold their blooms longer in a cooler environment. When in bloom keep them out of direct sunlight and away from drafts of warm or very cold air.
If your cactus gets too large, you can also prune them back by breaking off sections. You can fertilize after bloom to increase branching and future flowers. Cuttings a few segments long can be rooted easily in moist potting soil.
By the way, Easter and Thanksgiving cacti, which are in the genus Schlumbergera, are slightly different and many of the colorful Christmas cactus available in the trade today may actually be hybrids of the two genera.