I've been making mine with locally foraged plants, except for the fern that I bought. Not all plants -- even all mosses -- will thrive in a terrarium. Some of my moss died in the first terrarium but the rest is still going.

I find that it helps to get some bits of a live ecosystem in the jar. Wet leaf litter, worm castings, a chunk of rotten wood, that sort of thing. It brings in organisms that help balance the system. Plus I purposely gather pillbugs, a couple of earthworms, tiny millipedes if I can find them.

I may also try making a terrarium with tropical plants. There's a store with an excellent selection and they have a glass cabinet with plants that like humidity.