Hi
Looks like sphagnum moss for sure but there are many kinds . Sphag is used extensively for a potting material mostly for orchids , some types of carniverous plants usually dead, but can be used alive . gary

I made the buttermilk slurry out of this and spread it over a very large rock..It's inside, wonder if this will grow onto it?

Hi Gary, well I went and did a slurry with this stuff, with buttermilk then smeared it all over a huge rock in my living room. Will it grow?

hi
My guess would be no as MOSt sphagnum mosses are aquatic, growing in areas of very low pH often called "peat bogs" Since there are a gazillion types of mosses and dozens of kinds of Sphagnum mosses it's difficult to guess lol. Most of the commercial sources are harvested from standard "peat bogs" if you know the source of your moss
would help to identify it . Famous sources are New Zealand,Peru and most famous Ireland Obviously very different types ??lol You might google "Sphagnum" or peat bogs Good luck with your experiment!! gary

I don't see anything that looks like Sphagnum in that pic. Appears to be one or more pleurocarpous mosses.

The package it came in said it was grown in Saskatchewan, Canada, where I live actually.

Hi
There you go . i use a lot of Canadian peat to beef out my florida sand but have never tried to grow it just tropical sphags but then only as potting material
You might google the Id of Lycopus for some clueslol gary