Hey man, good luck with your DHG. I started a DHG carpet about 7 weeks ago- some comments:
First of all, it's a good idea to break your grass up as you did. I actually did larger clumps, and all these clumps grow poorly in a new environment and become an eye sore. I'm about to go through and remove some of the larger ones.
Dirt is nice, but I think DHG will grow well with column dosing as well. My tank, for example, is half aqua soil and half PFS. When I started dosing, the grass started spreading into the PFS and looks just as healthy as the growth in the AS. I do recall that for the first few weeks, the amount of nitrates and ammonia in the water were extremely high and the DHG went crazy during this period allowing it to get off to a good start.
Also, I added some faster growing plants that I eventually plan to remove to help keep abort extra nutrients and fight algae. I've tried growing DHG in lower tech setups and it always seems to grow, but eventually it gets taken over by algae. If your tank is lacking co2, I'd recommend doing something similar (except leave them in there).
A lot of people recommend trimming your carpet. I did one trim about four weeks ago and I'm about to do it again. Trimming is suppose to promote new growth.
Finally, the process is taking a good amount of time for me. I seem to be getting good growth, but still I think it'll be at least another 2 months before it's at the point I want it.