My experience with Java moss is that it takes a long time get really get attached to something and keep growing attached. Typically, it grows clumpy not like ivy on a wall, which is what I think you are looking for. I have had a nice clump of java moss in my tank for a year, and it is just now really looking like its growing really green and healthy at the points its attached, but it takes a long time. Plus, I have to keep trimming the stuff growing on the top of it giving it a hair cut so the bottom that is attached doesn't die off or recede