Looks like mildew. This is a common problem with hydrangeas from big box grocery flower shops, etc. Try some fungicide on the buds and see if that helps prevent spreading. However, blooms that are damaged already cannot be saved.

It's botrytis. Relatively common fungal disease that affects a lot of flowering plants and is usually focused on the flower buds or flowers themselves. Generally very closely related to weather - it will often show up if plants have experienced some cold damage or other stressors and with wet, mild springs - it can be reduced by increasing air circulation and avoiding any overhead watering. Too late to do anything now except you should remove and destroy any affected blossoms as the disease can spread. It won't hurt to treat with a registerd fungidice to reduce the chance of spreading to unaffected plants.

Here is a link that might be useful: Hydrangea botrytis blight

SpringwoodGardens and Gardengal48 thanks for your input. I'll do as you've suggested and treat accordingly. I was thinking it may be a fungus. I layed mulch a few days before, wonder if that's where it came from.

Thanks again, really appreciate your help!

I'm growing hydrangeas for the first time in containers and I was so happy to see a lot of buds but something is wrong with my plants. The buds are turning brown and the leaves around the buds are drying up and turning brittle. Is this botrytis blight? I can't see any visible bugs.

I usually see BB on open flower buds. You may also want to consider insect damage, damage to the flower and leaf buds during winter; or not enough water. You will need to use a special lens to find some of the bugs though; mites for example, can be so tiny that you will need to take another look with a special lens (check during the day aaand during the night for bugs).