I have some experience with growing Sphagnum moss, although it's mostly been in a plain terrarium with no animals. One thing to note is that there are many species. As I enter a one of my favorite small sphagnum bogs I see a light green form mingled with the sedges bordering the bog in and area that has some shade. Further in, under less shade, I see brown, red, and green forms. There are also forms that I see in deep shade in cedar or black spruce swamps.
In the terrarium I find these mosses in general like abundant moisture, cool temperatures, bright light, and little or no soil. They are quite vulnerable to fungi, especially if they are exposed to heat or excess nutrients. They both like and create acidic conditions. I usually water with distilled water. I am guessing that their environment may be too acidic for some amphibians, and also that animal waste might create an environment that was too nutrient rich for the moss unless it was a large lightly populated terrarium. I did keep a tiger salamander for years in a terrarium with a dead Sphagnum moss substrate that I changed periodically, so I think it's probably OK for some salamanders.
I find that the new growth on Sphagnum moss in a terrarium is usually green no matter what color the moss was when it was collected. This may be a function of light levels - I'm not sure. The photos show a front and a top view of a terrarium with two kinds of Sphagnum moss. The clump in the right hand corner was originally reddish brown. The clump to the left of it was green.
Most of my experience with moss has been from northern Minnesota. Because there are lots of species of Sphagnum moss, it's quite possible that my recommendations do not apply outside of the northern forest area. It may be, for example, that there are southern species that don't mind heat at all. Think about the habitat where your moss came from, and consider whether that's something you can recreate. But if you are going to put a salamander in there, also think about whether that habitat would be home to your salamander.
-Steve Morse
