Plants do not care how their nutrients are sourced - synthetic or organic. By the time they get into a form they can access, they are indistinguishable. Use whatever type of fertilizer you have or can access easily as long as it is recommended for acid loving plants. That will keep your Endless Summer nicely blue :-))

As long as you mulch regularly withy a nicely fertile, compost-like product you may not need to fertilize much, if at all.

Check how much you are adding since the lawn usually gets a heck of lot of nitrogen in lawn fertilizers. You said you were applying it at the "rate for lawn" and that may be too much.

Hydrangeas are not heavy feeders like roses are. An application (1/2 cup to 1 cup for newly planted shrubs) of organic compost or cottonseed meal in Spring would be fine. For those with a long growing season, you could add more in June-ish. A chemical fertilizer like Osmocote 10-10-10 applied per label instructions would be ok too.

I also sprinkle some coffee grounds after drinking my coffee or some liquid seaweed or liquid fish but I stop that at the end of June so as not to make the hydrangeas stay in growth mode before early frosts in the Fall. Of course, they always end up going dormant in Nov-Dec here but you may benefit more than I in stopping all fertilizers around that time. Too much nitrogen can also make the shrubs bloom less or none at all.

Thanks. I applied the milorganite at a rate of 36lbs per 2,500 sq ft. I'm beginning to think the issue with the hydrangeas might be a lack of water.