It looks like damage from a pest that starts eating from the leaf edges inwards so I would look for caterpillars and slugs and that kind of thing. On a day when you can check many times, go out at different times of the day, specially at night. You can also look in the soil and under rocks or leaves where the pests may hide underneath. Once you know what pest it is, take appropriate action.

Also, if you notice that the damage does not change and nothing is now causing more leaf damage, consider that the pest has flown away and make a note in next year's calendar to start aggresively looking for it by mid-May 2017.

Definitely, do not apply insecticides without first confirming that the pest is one that the organic/chemical insecticide does something to.

I second Luis's comments that all damage is on old leaves rather than new, so adding insecticide now is unneeded unless you find new damage and that it's important to ID the pest before using pesticides.

Sorry but I don't see any insect damage. Insects will leave holes or distorted foliage or skeletonized foliage and I just see brown spots :-) Brown spots are not a common sign of any insect problem. To be honest, to me these look physiological rather than pathogenic - caused by mechanical damage rather than a disease. And a bit too random to be a disease as well.

Mechanical damage can be caused at the nursery or during transport, when planting or even by the weather. Regardless, it is not anything I would be overly concerned about.

It is definitely more than just brown spots. I have seen leaves with chunks missing as well as shriveling edges and I am starting to notice damage on other plants. I have taken some more pictures that hopefully shows this. I inspected for pests a few times yesterday and again right now. I saw two dying slugs (from slug poison) and other than that, just some flies and wasps and one bumblebee. Really hope I do not lose these:(

Well, slugs (and snails) are fans of hydrangea/hosta leaves and they pig out on existing leaves and new shoots. They are nocturnal so you have to look at night and during the wee hours of the night to "catch them in action". You can remove them by hand, put chemical bait traps (think: beer traps), etc. These solutions work well for snails. Sluggo is good too.

I came across this when trying to figure out what is happening to my climbing hydrangeas--they look JUST like yours. First year I couldn't figure out what was happening, and they looked worse and worse as the summer progressed. This spring they looked beautiful and healthy with new leaves, but the brown spots have started again. I've tried everything I can think of. Did you ever figure it out?

Have you checked the soil to see if it is dry?

I have the exact same problem. I don't think it's a watering problem as it begins on the lower leaves. It really does make the plant look unsightly by mid summer. I guess I wil try a slug bait.

I found this thread through a google search. I'm having the same issue. I think I've discovered the cause. Spider mites. I took a close up shot of the leaf and zoomed in is the exact same thing I see online as spider mites. See the close up photo. Do you folks agree?

I will have to check mine out for mites. This has happened the past three summers. The plants start off looking great and by late june, the leaves start turning brown near the base and then it spreads up. Thanks for the post.