Answer: According to your zip code you are gardening in zone 5A, the coldest part of USDA winter hardiness zone 5. The bigleaf hydrangeas (Hydrangea macrophylla) are root hardy into zone 5, but they often suffer severe winter damage to the stems. When this happens, the flowering is reduced. The reason is that these plants bloom on old stems that grew the year before, so winter damage kills off the blooming wood. Spring frosts or late freezes can also damage flower buds.
Another common reason for lack of bloom is pruning at the wrong time. These can be pruned to thin them out or to shape them in summer after they bloom. Pruning at other times will remove flowering wood.
Hydrangeas do best in morning-only sun or in bright dappled light. Avoid planting them in full sun all day, or in afternoon-only sun. They need soil that is rich, organic and humusy, and it should be evenly moist yet well drained. It should be kept damp like a wrung out sponge, not sopping wet and not dried out. Using an organic mulch several inches thick over the root area will help to keep the soil moist and it will also help feed the soil slowly as it breaks down over time.
The best care for new plants is to water as needed to supplement rain, keep them mulched, and do not overfertilize. (A top dressing of compost or a slow release granular fertilizer at the lower rate per the label directions would be fine.) I hope this helps you trouble shoot.
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