Do you guys fertilize your hydrangeas? Specifically, Endless Summer, paniculatas, and oakleafs?

I get lots of flowers on all of them (except Endless Summer - but that's the topic of numerous other threads....) and lush, healthy growth, so I'm wondering if the bushes would benefit from fertlization (i.e. they're doing well, so should I bother).

I currently do not fertilize but do add a thick layer of leaf mulch every fall.

If you do fertilize, what do you use?