The bush is huge but not one bloom.
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Use a high-phosphorus fertilizer, such as 0-18-0 or 0-46-0, to encourage blooms. Bone meal is a good organic phosphorus source which gives good results. Hydrangeas will produce lovely green leaves if you use a balanced fertilizer, but they need high phosphorus to produce the best flowers. Work phosphorus fertilizer into the soil early each spring.
Pay attention to when and how you're pruning your hydrangeas. If they bloom on old wood and you cut them back, you're cutting of the flowers before they have a chance to bloom. Hydrangea's usually don't need much pruning and if they do you have to be very careful not to cut off the blooms. The buds are already on the stalks for next year's flowers. This article will give you some tips. Wishing you the best.
Here are some tips that should help https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/hydrangea-not-blooming.htm