Yellow Leaves on my Pee Gee Hydrangea Tree

Yesterday I noticed a number of yellow leaves on my Pee Gee hydrangea tree.  I know they were not there the day before.  I looked it up this morning and I found my exact issue on Garden Web.

A few days ago I hooked up the liquid Miracle Grow bottle to my hose and watered my beds, and two days later I have yellow leaves.  The person in the blog did the same thing.

My Pee Gee is in mostly sun.  Shade in the morning and later in the afternoon.  So, it's either nitrogen, like the Garden Web article says, or something in the "feed" is not good for my Hydrangea.

I have clay soil here that I amend when I plant the trees and shrubs (and plants if I have enough to go around).  Is there a general fertilizer I can use once every few weeks for my perennial beds???