Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Tie Riccia to small rocks and use these as retaining walls. Then slightly slope the substrate to the next wall. Or just make a carpet of these rocks.
I have always allowed Riccia to float. It will attach to damp surfaces, but I do not think it grows real roots, not the way you are hoping.
Try something that has real roots to mesh the substrate together.