Do you have a bushel basket or umbrella to give your Vanilla Strawberry Hydrangea some shade in the afternoon? If not, just plan to give it extra water until a good soaking rain comes along and the temperatures drop some. I have a hibiscus that I planted over Memorial Day weekend when it was above 90 degrees that is still fussing at me. The roots are working at growing and getting established. Plus, it is flowering. That takes a lot of energy and water. Every now and then, some of the bottom leaves turn yellow and the hibiscus is reminding me to give it some water. Next year, will be much easier. Your hydrangea and my hibiscus have good roots and will be better able to handle summertime stress.
Thanks for writing!