Photo?

In the ground or in a pot?

How wet is the soil when you put you finger into the soil as far as it will go?

Sun or shade?

Where are you? To add location and zone info to your profile so it shows up in all posts:

Go to Your Houzz in upper right of every page, click Edit Profile, and on the left side click advanced settings. Well down the advanced settings page is a blank labeled Climate Zone for Garden Forums along with a link to find your zone.

If you add info on your state or the nearest large city you will get even better information since zone only relates to average coldest winter temperatures.

Then return to the top of the page and click Done Editing.

Check these out:

http://www.aces.edu/pubs/docs/A/ANR-1212/ANR-1212.pdf

The only common looks that resemble boiled spinach are anthracnose -a fungal infection- or Fall color foliage changes like after a frost zaps the leaves. But constantly wilted leaves in soil that has moisture suggest root rot. So, check the article on the link.

It is in the sun. In the ground not a pot. I live in Suffolk County, Long Island NY. I water twice a week as needed. Other plants in same area of the garden Azaleas and Burning bush are doing fine.

If the soil does not drain well, try to keep waterings in check. Hydrangea roots do not like to sit in wet soil for too long. Oakleaf hydrangeas are THE mopst sensitive ones. Consider too that they cannot absorb oxygen in wet soil and that, along with heat stress, can also trigger yellowing of the leaves. A guide to watering is the finger method: insert a finger into the soil to a depth of 4" and water if the soil feels dry or almost dry. You can give them 1.5 gallons of water per watering during the summer... or 1 gallon in the Spring/Fall when temps go down. Use 3-4" of mulch too.

If this is a recently planted shrub, it will be more sensitive to the sun and moisture issues on its first few years in the ground but, again, try not to go overboard with waterings.