This early in the game: protect, protect, protect. 30 would be a moderate freeze in my book. Many people do not realize that frost forms sometimes as high as 35 degrees because the temperatures they report are for about 6 feet above the ground...where a thermometer would be. Heat rises...so 30 could mean more like 26-29 where your hydrangeas are: on the ground!

In short, I never take the chance.

Your leaves will recover if the frost kills them. Not so sure about flower buds. But even if you loose the flower buds, ES will rebloom later in Spring and give new blooms, albeit later than usual.

To protect it simply make sure that it is heavily mulch at the base and throw a blanket on the plant. Make sure that there are no gaps where the cold can get in through. Also use something to hold it down in case of wind. In the morning, after 9 or so, carefully remove the blanket.