Have patience. This has been a long cold late winter in lots of areas and things seem to be running a little behind on showing their growing tips. If the plant has been doing this well for so long, chances are it's just still laying low waiting for warmer weather. (Mine was a little late this year but it's about a foot tall now in zone 7.)

zone 5 here..just starting to see the first signs of life... just be patient...

I'm in zone 5, and mine has not shown any sign of life yet, but 3 "unnamed" other ornamental grasses have shown good life signs.