When & how often to repot?

[tinarae]

I think it's been 3 or 4 years since I've changed the medium in my mini slc. How often should it be changed? I hesitate to do it when there's new growth, but that's pretty much all the time. I have mostly minis that never really outgrow their pots, but I do worry about the quality their bark. How about orchids mounted on sticks? Does the moss ever need to be changed on those? How would you even change that?