Mine were growing fine in eco-complete until I let my pygmy chain swords take off and they sort of overtook the expanding DHG patch and it mostly died out because it wasn't getting enough light (the chain swords grow much faster). I decided I liked the look of the chain sword better (more grass like, stays short) so I'm letting that form a carpet in my tank.
Plant the DHG in very small bunches and if they are doing well they'll send out runners pretty quickly, and as long as you don't have anything competing for the same space they should spread and fill in nicely
I've had them grow in gravel without any care and they did great for a few years, but got killed during an Eco-system collapse only survivor was an anubis. Don't trim it let it grow it's own way, it will send runners out on it's own and spread. Good luck!