I'm not sure what one is supposed to do, but my big, healthy Annabelles and Nikko Blues are planted near trees--lots of leaves fall on them in the fall. In the springtime, I usually leave them there, maybe taking off some if it seems to be too thick.

I planted two new paniculatas this spring and added mulch around them. They are growing great. Will see next spring if I need to remove any leaves or not.

Kate

Yes its a good idea to mulch around your hydrangeas. It helps keep some moisture in and it also helps to keep the roots cool in the hot sun. I generally mulch slighty further then the hole i dig which is about 2-2.5x the width of the pot the plants come in.