Hello, mynewyard. It looks like a fungal infection to me. Wet rainy weather or humid conditions favor or contrinute to the development of these problems in large leaf plants like hydrangeas. Oak leaf hydrangeas suffer from this problem because of over head watering at the nursery; many people ignore it as new leaves will not have this problem.

A more serious fungal infection is anthracnose. It appears as brown to black irregular blotches in the leaves. I included a link on Hydrangea Diseases below for more information. Daconil and Cleary 3336 fungicides are recommended in this case. Dispose of fallen leaves and plant debris in the trash. Minimize splashing water on leaves and humid conditions by increasing airflow around plants that are planted too close to each other.

How much water does this plant get and how often? Do you water it with a hose or do you have a sprinkler system? Watering the leaves promotes fungal diseases; watering the soil under the plant is better. 1 gallon of water twice a week or so in spring is a good starting point. To check if you should water, insert a finger to a depth of 3-4 inches into the soil. If it feels dry, water. If it feels wet, the plant is getting too much water or the water is not draining well. After a while, you should get an idea how often to water. In the summer, increase the amount of water and reduce it in the fall.

I did not notice any mulch in the photo. Does it have some now? Three/four inches of mulch should do it; add some through the drip line or a little further.

Luis

Here is a link that might be useful: Hydrangea Diseases

Thank you for responding. We have not put mulch down yet, it's in the plans for this week. The hydrangea has only been in the ground for about a week now, maybe less, I can't remember, but I had watered it almost every other day since planting it. At least one of those days it was with an overhead sprinkler. Thanks for letting me know I should not do that. I will check out the link and the fungal infection.

My hydrangeas were beautiful for the 3 months after I planted. Now the leaves have holes in them, turning black and the flowers are wilting before they open. The ones that are open are turning green and have lots of brown buds
What can I do to save them?