My grandmother had a Christmas cactus that my mother inherited. My mother repotted it with another Christmas cactus. Now I have them. The newer cactus blooms but the old one never does. Why? Should I separate them?
It is quite puzzling why one is blooming and the other one isn't. Did your grandmother's bloom for her when she had it, and if so at what time of year? And how long have the two been planted together? Possibly the older cactus is one of the species that blooms at a different time of year. Possibly it just didn't like being moved and repotted, or being repotted with another plant. It sounds strange, but plants can be fussy. However, if the two have been potted together for very long, it might not be wise to separate them if the roots have grown together. If the two can be separated without disturbing the roots much, you might try that. If they can't be separated, continue caring for them as you have been, and let the old one (hopefully) adjust. Here are a couple of article that might help you: https://www.gardeningknowhow.com/ornamental/cacti-succulents/christmas-cactus/repotting-christmas-cactus.htm