Growing cubes on paper or cardboard is possible but you will most likely not harvest a whole lot of mushrooms. Most of time you will get a lot of pins that don't mature to a significant size. Sure is fun to watch though. I once had a mason jar with cardboard disks in the bottom noc'ed up with cubes. That jar sat in north facing window sill for years and would just keep popping up these lil half inch size shrooms, they would wither up and new ones would grow. The only thing I ever did to that jars was add a few drop of water once in while. The jar just kept growing year after year until I finally moved, I left it behind as I didn't want to have to pack it up.
Edited by coorsmikey, 13 January 2015 - 04:03 PM.