Are sure you mean a hard freeze? In gardening terms, a hard freeze is defined as period of cold that kills seasonal and deciduous vegetation (i.e. annuals), could damage new evergreen foliage, the ground freezes and heavy ice forms in any puddles or water collection recepticals.

I know you experienced a rather sharp temperature drop, however I'd guess it was only a hard frost, in which any remaining annuals and deciduous foliage was affected. It takes quite a bit more than that and for an extended period to damage hydrangeas in your climate. Just leave the plants alone. You can remove the blackened, frozen foliage if you wish or if the plants are very visible and deadhead any remaining flowerheads but it's not necessary. Don't cut back. In the spring when new growth is evident, you can remove any obviously dead wood but you don't want to do any heavy pruning, either now or then, otherwise you may remove very viable flowerbuds and reduce or eliminate flowering.

Winter protection of hydrangeas in zone 8 is pretty much unnecessary. The exception would be a late hard frost in spring after new growth has already begun.

For you, it's not the cold that will get them. I've got some Hydrangeas sitting in my house right now that endured 17 degrees outside a couple of nights ago. They're fine.

It's next Spring when the buds break dormancy on some fine 60 degree Spring day only to be followed a week later with temperatures in the 20's. That's what gets you people in Georgia.

Dirr has made the point that you get more consistent flowering at cold Cape Cod than you do in Georgia. All because, at Cape Cod, the ocean doesn't allow for the extreme swings in temperature.

Hay

rjinga, don't cut them back. Unless we have a hard freeze, below 15*, you shouldn't worry about them. You may want to mulch the roots if you fear a hard freeze. All that has happened is the green leaves have been blackened. You will need this year's growth for next spring's blooms on most hydrangea varieties. Dead head the old blooms and when the leaves are crispy-dry, they will disintegrate. By spring you will have clean stems. Sometime in February you may want to give them a shot of liquid fertilizer with a high middle number, like a 10-20-10.