I live in the Midwest USA and I'm making plans for a rock garden inspired by one in Japan. I would probably need something tolerant to winter temperatures and hot summers, along with a mostly sunny lawn (I've got 2 trees packed into the corner of my backyard, one large birch, and one maple that's ~13 feet tall), just a generally hardy species that can tolerate the climate of the Midwest.
What's the best species for this garden project?
I suggest walking in a woods to look for a local moss suited for your location. You may be able to collect some to get started. I have a small pond surrounded by rock in E.TX, Now 25 years old. A native moss volunteered after a few years and slowly grew in cracks and seams. I did not start it , but after it started , I moved pieces around to speed spreading. In my experience garden shops do not stock moss, especially the chain stores. A friend had a small garden shop with an extra wide variety. My moss start may well have been a hitchhiker on plants I purchased.
Two species I've found that purportedly are "sun tolerant" which is an abnormal trait for mosses in general (though if you put them in competition with grass, you'll have a project keeping them from being overtaken by grass in sunny areas, I think...)
Bryum caespiticium (according to some, "sidewalk" moss)
Leucobryum glaucum (pincushion moss)
Can't swear they will work for your situation, but if you can't find any local (-ish) moss to transplant, might be worth a try to see if either or both works for you. Appear to be commonly available via specialist suppliers online or via mail-order.
