I bought 3, 3-gal endless summer hydrangeas and potted them over a month ago. All three were planted in good quality potting mix, receive morning sun and afternoon partial shade. All have grown tremendously and are starting to bloom. However, within a week of potting them one of them started turning yellow. The other two have progressively started yellowing as well, but still not to the extent of the first. I have read about over watering, nitrogen deficiency (bought a ph tester), and also iron chlorosis. I have since applied some epsoma soil acidifier as I figured lowering the ph couldn't hurt anyway...since hydrangeas certainly don't mind. Not sure what to do next. It is hard to tell if the yellowing is on mature leaves or new, or just both. Should I buy some iron plant tonic, increase drainage/lay off watering, or a little of both?!? They seem to be doing well, since they are all starting to bloom regardless. The two photos are from one of my plants that has shown the most yellowing. Please help!!