Thick lush background plant that spreads by runners?
In my 20 long I have a nice carpet of dwarf hairgrass (eleocharis parvula) and about 3/4ths of the way back I have wall to wall rocks. Behind the rocks there is a 3-4 inch area where I currently have no plants.
I'm looking for a nice background plant that will create a thick wall of plants without requiring constant trimming and replanting.
I have already tried eleocharis vivipara, which really only spreads with aerial runners. I have eleocharis acicularis in there now, which everyone says should get tall enough to form a background in a 20 long, but I'm skeptical (it's still fairly new to the tank and hasn't really taken off yet)
corkscrew val may be my best bet, but it's hard to get a really lush full look with val, as it tends to spread out quite a bit when it grows.
Does anyone know of any other plants that would meet my needs?
edit: Also, I should mention that this tank has co2, med-high light, and EI dosing.