Have you pruned them differently last / this year? They flower on old wood so need to be pruned in April. Cut off the dead heads then and any old wood, then take out a little of the older stuff if the centre of the bush is overcrowded. Cut to just above a pair of buds.

If it's not a pruning problem, maybe the strange weather we've had this year, with extremes of cold, heat, drought and heavy rain alternating all season have thrown it out of kilter.

I agree and think it's the weather, hydrangeas like a lot of water and we have two hot and dry periods once when the buds were forming and again later when they should be flowering. Mine have flowered poorly and many of the buds just withered and fell off.. Did you get no flower buds at all? if so I agree it was probably the pruning.

The ferocious cold last winter probably played a part, also. Hydrangeas form their flower buds the previous late summer or fall, and a hard winter like that can easily damage the flowering tips.

We had a visitor from Germany quite a few years ago and she was amazed to see our great big hydrangea bushes growing in the ground. Where she lived they're tub plants to be taken into shelter for the winter. Just goes to show how easy we usually have it.