Every time I've tried to cultivate moss, pillbugs eat it. I've never bothered to try to clean it because I was doing this outside. My 2nd mini garden started with a beautiful carpet of moss but it didn't last long. A container or vignette of just moss would qualify as a mini garden, IMVHO.
I do love moss though, sometimes it's the greenest green. I've always been one to stop and caress dense, smooth moss while hiking. There's some cool moss on a wall behind my office and it makes beautiful red stems when it "blooms." The only place I don't like it is on a patio or walkway, too slippery.
