A Christmas cactus is very easy to pass along. Just break off a segment or two and put it in some potting soil. Keep it out of direct sun until it roots. I often put them in the pot with another plant where they will be shaded by its leaves until they root and take off on their own.
That first plant from my grandmother? Well, it did not achieve heirloom status. It succumbed to sunburn and drought because I left it on a hot brick patio all summer. Don't cacti need hot sun? This plant is a member of the Cactaceae family, but it would have been better to call it a succulent and forget what I knew about saguaros. Schlumbergera comes from the cloud forests of Brazil, not the deserts of the American southwest.
|Schlumbergera truncata blossom, Wikimedia Commons|
Schlumbergera truncata loves humidity. North Carolina summers are plenty humid for it, but during very dry spells and indoors, you might want to mist it occasionally to mimic its cloud forest home.
Once night time temperatures begin to drop, let it get quite dry between waterings -- even to the point of wilting a bit won't hurt. Leave it outside until just before the first frost.
Then, if you can, keep it in the sun in a cool room for a few weeks. In my experience it does best with a drop in temperature at least at night in order to set buds. I have had one set buds on only the branches touching a cool window in a 68 degree room.
If you want amazing Christmas cactus blooms all year long, or would like to add a "Wow, cool!" to your day, watch this video of Joost Langevelt making an origami Christmas cactus.
Here's a useful article for you - How to tell the difference between Christmas, Thanksgiving and Easter Cacti
|Zygocactus_bonsai.jpg by Emmanuelm, via Wikimedia Commons|
Now that is an heirloom Christmas cactus!