i doubt it .. that really isnt that cold ... but you might have some die back by spring ...

did you cut them to the ground and mulch them????

here in MI ... my H usually die back to about 2 or 3 inches or so .... and then in spring.. i cut them back to the lasst 2 buds or so ... which is simply normal procedure for colder zones ... and perhaps foreign to your zone ...

so bottom line ... they may get forsted.. they might look like carp ... but i highly doubt they will die ... it simply wont get cold enough for the soil to get that cold ...

you can simply cover them with boxes.. if you can get some from the grocery store ... or have then around .... just to TRY to keep the leaves from freezing ...

ma nature is a witch ... we do the best we can ... but dont get discouraged by her whims ... one should NEVER BE TERRIBLY WORRIED ... it kinda defeats the idea of relaxing with gardening ... [yeah,. good luck with that.. took me about 20 years to get to that sate of zen .. lol]

what will be.. will be.. and i doubt ... that this cold snap alone.. will kill them [BTW its been hovering in single digits here in MI every night for about a week ... and i hadnt given my H a thought about it dying]... but they may assume a new shape .... after you have to prune back any damage ...

contemplate.. but dont worry ...

ken

They should be fine. Mine have buds and very small leaves just emerging. Normal in my case and I'm in Zone 8 near Seattle. Colder weather will happen before the year is out. Never had a problem in many years of growing Hydrangeas here.
Mike

Thank you both. Yes, I am not worried that they will die, just that the new growth and buds will. I planted them last spring and summer and Zi am so excited to watch them this spring. It would be understandable, though disappointing if the harsh weather ruined the show. Good to know yours are fine in the same zone Mike. I may be pruning them like crazy, Ken, if I get too much damage. Good to know they will bounce back so well if I have to.