I spoke with Carrie @ Great Lake Hops today. She suggested that the hops may have gone dormant - they arrived in early February from Michigan where they were dug out of the hard ground while dormant. When I received them, they were planted within a few days.
Carrie thinks that perhaps because they were in a cycle of dormancy, forced out of dormancy (by planting), then went dormant again.
This theory does explain why there was a small growth spurt then nothing since ...
Does this sound plausible? If yes, and these are indeed dormant, what can I do, if anything, to break the dormancy and start them growing again?