Andrew - many of mine sound like yours, short (some wimpy) and not as tall as I'd expect. Some of us are going through this right now. I don't know if we're too anxious to see progress.
I have some around my Limelight hydrangea as well!
Mine were all planted with a handful of Superphosphate so I'd have thought I'd get more growth by now.
I'm hesitant to recommend any supplement since I don't know if it's our weather (too dry but our irrigation system goes on four times a week, 45 minutes each zone) or if there's another reason for it. Hopefully, someone will post with a remedy.
