Hydrangea Not Blooming?

I have 4 hydrangea plants. I planted them at least 4 years ago, I never trim them, I just leave them the way it is all year round. I planted them, some in the shade and some in the sun. For many years, they never bloomed. Last year 1 of them suddenly bloomed 2 flowers, but the others still never bloom and this year none bloomed.

The leaves are always green, big and healthy, just no blooms. What is wrong with my hydrangea? I used slow released liquid fertillizer with the middle number higher, but still no bloom.
What can I do to change it? Here is the picture of last year's plant with bloom, it had 2 pink flowers, changed from cream to pink.

By Sharon C.