Answer: You're wise in seeking out the hardiest hydrangeas to grow in your garden. Those that you have bloom on new wood which is produced on old wood so if the entire plant dies down to ground level each winter, you'll never get blooms. I'd suggest replacing it with something more cold hardy and something that blooms on both old and new wood. Here are a few suggestions:
'Annabelle' is a very cold hardy hydrangea that looks somewhat like a mophead. It is white and ages to an attractive light green color. Authorities claim that it can grow as far north as Zone 3a.
PeeGee (Hydrangea paniculata 'Grandiflora') does best in cooler climates such as yours.
Endless Summer Hydrangea (Hydrangea macrophylla 'Bailmer') has the ability to bloom on old wood and new, and will bloom from mid-June until the first hard freeze. this is the best hydrangea for your gardening region. Plus, the Endless Summer Hydrangea is an instant soil tester. If your flowers are blue, you have acidic soil. If your blooms are pink, you have alkaline soil.
Best wishes with your new hydrangea!
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