Q.What Fertilizer Specifically For Hydrangeas?
I’ve been using 12 12 12 all-purpose.But I want to see more blooms.

Certified GKH Gardening Expert
Hydrangeas don't need a lot of fertilizer. Less is more in their case. Your general purpose fertilizer is just fine. If you want to try a bloom booster, add more phosphorus (the middle number), such as 12-20-12 or bone meal. If the leaves start to burn, you are adding too much fertilizer.
Low flower production is usually due to too much shade (morning sun is ideal), too much nitrogen, or pruning at the wrong time.
https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/fertilizing-hydrangeas.htm