I want to start new plants from my large old one. How do I propagate cuttings – in water? in soil? Is there a special way to make the cuttings?
There is no one way to propagate Christmas cactus cuttings. They certainly can be rooted in plain water, although they sometimes rot before developing roots. I think you are more likely to have success if you root them in a potting mix.
Each stem is composed of visible stem sections. The base or lowest end of each section is capable or producing roots. So take multiple cuttings that each consist of 1 to 3 sections. Insert the bottom of the lowest section upright about a half-inch deep into the potting mix.
Use a peat-based potting mix or make your own mix of 4 parts peat moss and one part perlite. Get the peat mix nice and damp and fill one or more very small (2 or 3 inch) pots with this mix. I suggest inserting 3 or 4 separate cuttings into each pot. Multiple cuttings in the same pot will make for a much fuller plant later on.
Keep the cuttings pots in a warm moderately sunny location. The tricky part is keeping the potting mix constantly damp, but not wet. The roots need both moisture and oxygen to emerge. When they do emerge they are very fragile and will easily rot if the mix is too wet or dry up if the mix gets too dry even just once.
Some folks put the small pots and cuttings into a clear plastic bag and seal it tight. This keeps the moisture inside the soil and in the surrounding air. If you do this, keep it out of any direct sunlight to avoid overheating the cuttings.
These cuttings will root very slowly so you will have to be patient. You will not see any changes for several months, but as long as the cuttings remain firm and upright and green, they are on the right track.