Posted: 26/07/2015 at 20:35
Yes,,that soil is too impoverished Snarly.
Fish blood and bone,,or any fertiliser, is not same as putting goodness via compost,,manure, into the soil.
Hydrangeas need good, humus rich soil to do well.
Can you lift your plant and incorporate some goodness into the soil?
I think it's probably the reason why your other hydrangea is not flowering...viz., that the soil there too is poor.
Forget the fertilizer...it's a bit like us taking loads of vitamins with a diet of crisps!
Get the soil right and you will grow everything better