Answer: The most common reasons for lack of bloom are either pruning at the wrong time or the plant is not cold tolerant enough -- meaning it is root hardy but not bud hardy in your area.
If it was originally a florist's hydrangea for example, it is probably a winter hardiness issue. Most of these hydrangeas bloom on old wood, meaning branches that grew the year before. Winter damage to the branches or pruning in fall, winter or spring will remove the flowering wood for the coming summer. Spring frosts can also damage the buds for the coming summer.
You might try giving it a good wind break, or as extra winter protection you could make a frame around it with burlap and fill that with nonpacking insulating material such as dry oak leaves or straw, and top it with plastic or a tarp to keep it dry. Leave air gaps to avoid condensation and heat building up inside. Put this on in very late fall after the plant is fully dormant and take it off in mid spring. Then be prepared to cover it if spring frosts threaten.
Maybe you will see blooms next year. Here are some more tips you may find helpful.
I hope this helps.
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