I got my DHG from petco also. The first batch I tried to, seperate to spread it out a little so it could fill in better. They where so tiny I couldnt keep them in the substrate. Every day I'd look and there would be more and more floating, of course I think some of this was because the ghost shrimp and MTS wouodnt stay out of it! Lol.
Anyway, the second batch I just took scissors and cut it into thirds and planted it that way. It did fade a little and a few strands "escape" once in a while but it seems to be perking back up and getting greener now. I've had it about 3 wks. It's in my 6.6 gallon bookshelve tank which is shallow (approx 8 inches after substrate) so the DHG does get some light. It's a 15 watt, 6700k bulb.