These hydrangeas live in zone 5 (Northern Ohio) and have very luxuriant growth but don't flower. There are no dead or wilting leaves. The plants don't get much sun. Is that the reason they don't flower?
I am guessing these are this year's growth, i.e., no old growth stems at all. These are macrophylla (big leaf - mophead, lacecap) and bloom on old wood (last year's growth). More than likely you either pruned off last year's growth along with the blooms or last year's wood didn't survive your winter which is apparently common in colder regions. So this winter you need to winter protect these stems for next year's blooms. Luckily I don't have to worry about that but there are plenty of suggestions on how to accomplish this on line. The one I see suggested most often is a cage around the plant filled with fallen leaves to give some insulation.
You can get paniculatas which are very hardy for your area or reblooming macrophyllas that are supposed to bloom on new and old growth.
Last spring I was shopping for Quickfire hydrangeas and the one I liked best was the largest one with the biggest, greenest leaves, but as I approached the plant I suddenly remembered Judith King's advice (from the website link). So I walked back along the row and found the one with the most blooms. It had a lot of annoying dead branches but it was covered from top to bottom with beautiful white blooms (springtime color is white-now it's pink). When I brought it home the blooms increased and it has been full of blooms like a beautiful bouquet ever since and no end in sight (see attached photo taken today after the rains), but the front (top of photo) facing the morning light has more blooms. - DoGooder
Hydrangea's need good sun and do best when there planted into a good rich loomy soil, that is soil with added leaf mould or humus by adding well rotted horse manure to the planting holes at time of planting or as a topsoil addition that can be forked into the soil around autumn time.
Also at what time are you dead heading ? pruning the shrubs, dead wood in never going to foliate when brown / dead so remove this dead growth and this will allow air and light to enter the inner area of the shrub making an open healthier plant, this also allows any buds to gain from the sunlight air and even insects that help pollinate the flowers when they do come.
Hope this helps a little.
Best Regards. WeeNel.
The plants aren't getting dead headed because we're not getting blooms to deadhead. They were planted several years ago. Yes, we get winters down to zero degrees F.
When should I wrap the plant? It holds its leaves well into November. What is the best way to wrap the plants (they're a bit large and difficult to wrangle). There has been a problem in that come spring the insulating leaves are wet and rotting. I've never pruned the plants. Maybe I should cut them to the ground and see what happens? Thanks for any additional advice!
ken33, I read that the macrophylla (big leaf) hydrangeas are more sensitive to cold frosts than all other types of hydrangeas. They don't like erratic weather such as during spring the weather becomes warm then the warm weather is followed by a late cold frost. They often die under those conditions or the new growth will die. It looks like you have one of the big leaf varieties so the problem could be the cultivar is not ideal for your environment.
I only have one big leaf (round ball) hydrangea but I chose one of the hardier ones (All Summer Beauty) which has been known to grow very well in MA which has very erratic weather. Here is a web page that better describes the types of hydrangeas appropriate for different climates: