Heat stress affects the blooms just as it affects the leaves. As temperatures go above 85F, the sunlight, temperatures and the hot winds tend to help dessicate blooms. This shows up as browning of the sepals in warm locations. The pink sepals can also fall off. It can be common with new shrubs whose root systems are still small. I notice it in newly planted (like last year or this year) shrubs sometimes.

Sometimes you can help alleviate the conditions but other times there is little one can do. Keep the soil well mulched so the plant roots do not quickly dry out in the summer. Keep the soil as evenly moist as you can, increasing the amt of water if you have not already done so. In some places, it "is summer" just because of the hot temps. Place the shrubs in locations that are not windy. Give them morning sun only until 11am or so (the earlier, the better). You could even try blocking the direct sun with umbrellas and, chairs, etc but start with regular waterings with more water than you used to use in the Spring.

But once really high temperatures show up, it is like you would have to encase them in an igloo to help. That is when no matter what, the blooms show signs of browning. So first start researching if the soil is getting dry or needs an increase in the amount of watering per plant. Of course, if the soil already feels moist then no more water is actually needed and too much water might cause root rot. Increase the amount of water thru summer. But at points at or above 100 degrees, they just have a hard time not browning out.

Down here, we are already getting 100-degree temps so I know the blooms are at risk. If you have a rebloomer, it will produce new blooms at some point. It is then when I may choose to deadhead any blooms from Spring that browned out in late Spring or early summer.

I also observe that the second flush from reblomers tends to show up once the summer temperatures moderate, meaning when they come down from the 100s. Very few shrubs like to put energy into blooming anything when it is hot so I expect the hydrangea bloom crop from Spring to brown out and then get blooms from new growth closer to the Fall.

If this is a new shrub for you, see how it performs and when it decides to produce a 2nd flush of blooms for you in SC.

I have seen (in some random years) recent looking blooms in Greenville when I visited relatives in August. Your coastal weather may help moderate things though.

Browning and the fall of sepals unfortunately, cannot be reversed. But if it bugs you then consider deadheading the blooms early.

Heads up.. remember that in the South, some hydrangeas will soon be developing (in July-August) invisible flower buds for Spring 2019. If you need to plan any type of pruning, now (the month of June that is) would be a good time to prune (if you need to).

Note: there is a small chance that some pests like deer may also have nibbled on the blooms but, they left the rest of the shrub so pristine that I did not consider that possibility too long. They were messy eater iwhen I was in Georgia. Thus, I decided to mention that that was possible but that I ruled it out. I could be wrong though.

Luis