ok thanks for the helpExo Terra has a tree fern substrate that is already milled tree fern. It's much cheaper to buy that.
However, broken up tree fern won't be as effective as a growing medium because you'd only be able to silicone a thin layer to great stuff or glass. I can't imagine it would be any better then peat moss or coconut fiber (eco earth)
One option would be set the panel in the GS as it cures. That way you still have a thick sheet of it as a growing medium. You can even carve the panel as you would GS to get a more natural look.
It will grow mosses and ferns but you need to add moss spores and fern spores.on the label, it says that these will grow moss and ferns after being kept moist... if u break the panel up and silicone it to great stuff will it still grow moss and ferns on it??