now that you mention it..and i stop to think about it more, the acicularis grows faster, yes, but the parvula grows at the same rate.
I do not find hair grass to be much maintenance. I trim every month or less, if i want to encourage runners. I've been wondering about keeping it contained and have considered using small plastic containers as a pot within the substrate for E. acicularis to see if it would prevent runners from spreading elsewhere. That way I could have tall bunches of grass in a field of shorter plants like HC, E. Parvula, or dwarf riccia and not have to cut off runners if I want to maintain the look. I want to do an iwagumi-esque layout with a grassy field/meadow look.