...Periodically, they insist on dropping branches. They seem fine and then just drop large healthy looking limbs. My plant is slowly getting sparcer instead of larger. Any ideas?-Sue
Sue, since you don't make any mention of disease or pests and say that your plant loses healthy limbs this may be an instance where "it just happens" or we may have to do some plant detective work.
The fleshy stems of Christmas cactus (Schlumbergera) hold water and it may be that you're watering too much. But overwatering would usually be accompanied by root rot or some visible signs in the leaf segments of this cactus or flower bud loss.
Also, you don't mention where the stem loss is occurring on your plant. Are the stems that are falling off on the outside of the plant or is it losing stems from within the center of the plant? If it is the outside of the plant have you considered the possibility of people or pets brushing up against it and breaking off a piece? You mentioned in the comment that you live in an area where you can now grow these outside; besides people and pets maybe it is being visited by squirrels, birds or some kind of "garden pest." If the stem loss is occurring within the center of the plant it may be because of low light. When sufficient light fails to reach the center of a bushy plant it will drop leavs from the center and branches die back.
Why I think it may "just happen."
Think about where these plants are native to and how they grow there. They can be found growing overhead in the tropical rainforest. Another clue could be the design of the plant itself. Why did the plant evolve to grow leaf segments that break and root easily instead of a long vine like an ivy? We know that the plant grows high up in tree branches so maybe the stems breaking and falling off is a necessity. If a Schlumbergera is growing high up in a tree and a branch breaks- it falls and perhaps gets stuck on a tree branch below. Withing a few weeks the piece that broke off is rooted, growing and a whole new plant is created. You can use this to your advantage by rooting the branches that break off and planting them back into your potted plant. See my entry on Rooting Christmas Cactus Cuttings by following that link.
Some things I think you can safely eliminate as the cause of your branch loss.
Underwatering: The branches wouldn't look "healthy"- they'd shrivel or turn brown and crisp.
Cold temps: If your plant was exposed to cold temperatures it would also show signs in the branches and leaf segments. The color would darken to a black or brown and become mushy.
Hot temp: Again the branches would turn brown and crisp from drying out.
Hope this helps and thanks for stopping by and asking a question that gave my brain a workout.