My first thought is fertilizer. What kind are you using? If you are using one that is high in nitrogen, it will grow leaves rather than flowers. Use a fertilizer that has a higher middle number of the NPK ratio. P – phosphorous is the number you want for flowers. Next, let’s look at pruning. It’s really best with hydrangeas to plant them in a spot where they have room to grow to their mature size and avoid pruning. That way you don’t risk cutting off the flower buds. How much sun is it getting? In your area, hydrangeas will flower best in full sun. Finally, water. I make sure to really water shrubs that grow flowers. They seem to need that extra boost of energy when it’s time to put on flower buds and flowers. Another thought, overwintering. I wonder if it needs a little extra mulch for winter. That way it doesn’t spend part of spring recovering from winter and is ready to grow! I hope these ideas help with finding a solution.
Thanks for writing!