When repotting a Christmas cactus, it is best to wait until the end of winter when the plant has finished blooming. Christmas cactus should be repotted every 2-3 years, or whenever the roots begin to grow out of the pot. Choose a new pot that is 1-2 inches larger than the current one, and use a well-draining cactus soil mix. Be sure to handle the plant with care when repotting, as the stems and leaves are easily damaged.