Bee-dubya-ell makes a good point about drainage. Mosses need acidity and moisture, but drainage is essential to good growth, otherwise molds and rotting becomes a problem.

The problem is severe with epiphytic orchids (those on trees), which naturally receive rainwater and the organic nutrients in the runoff. Trying to judge the proper balance in a greenhouse situation has frustrated many who lack patience.

Someone also recommended the use of local mosses, or those recommended for your climatic zone. There are many species, some do well here in deep-frozen Alberta, if dappled sun in summer, good drainage, slightly acid conditions and moisture are provided.
There are some small flowering plants that do well with mosses; forest floors with the right conditions are beautiful with their lilliputian gardens.