Oh, no. Depends on how long sub freezing temps will stick around. I have had lows of 30F that did not faze the plants but they were watered deeply the night before and I had mulch around them. It was also an overnight kind of a thing in that temps dipped and then went above freezing as the next day wore on. If the sub freezing temps dip below into the 20s for a long time then I would protect the plants anyway you can as the flower buds are in a fragile state in which they could get damaged. If the leaves get zapped then you may have to wait a few weeks/month in order to get new ones. I feel your pain as I recall having to put chicken wire cages for winter protection in late March when temps dropped to the low 20s and a handful of the plants already had a few broccoli heads open. Sigh. Good luck!

What kind of hydrangeas are we talking about?

It’s only nights that will dip below 32, each day forecasts show above 32. Most of the day hours of next week are supposed to hover around upper 30’s/lower 40’s. Of course that’s only the forecast, who knows what temps will do when it’s actually happening. So, in addition to covering them, it would probably be a good idea to keep them well watered, right? Thanks for answering btw!

Macrophyllas

Yes, water, mulch, cover them and knock on wood! Good luck. Hope you get many blooms.

I am zone 5b and have three rather small panicle hydrangeas (just planted last Fall). I covered them today. I used some stakes that were taller than the shrubs, then added a frost blanket on top. I have these frost pillowcases I got online that work well. It's probably too late to be giving you advice but for what it's worth, I'm covering.

If you had leaf out of paniculatas already, a late frost may zap the foliage but new leaves should "return" in around 2-4 weeks.

update: so far I’ve managed to get all my hydrangeas growth through this week, which surprises me, because lows last night and yesterday night were 25! I thought I was gonna uncover them to find their buds warped and blackened, but to my delight they’re still green!

However, I’m not in the clear yet... It’s supposed to be a bit warmer tonight, hovering around 31-32, but get this.... we’re supposed to get 3-5 inches of snow. Which leads me to yet again ask if I should protect them, or if they’ll be alright? Just not sure because the ground is still warm enough that the snow will probably melt, which means the stuff I throw over them will probably get wet. I don’t know if wet things sitting in the hydrangeas will just make it worse for them or not, but I’ve gotten them this far, I’d hate to lose them now!

We cannot see the future but I would throw something on top as your concern is not the temperatures but the flower buds in those mopheads.

I understand how you feel. I took my tropicals outside around mid March or early March. Then the last five days, we have been going don to the upper 30s. I had no recourse but to leave them out as I did not expect this and realized it one morning when I went out with the dog and it was already 38F. Ugh. Good luck and tell the forecasters to quit these cold temperatures! Ha! ;o)

I read on usatoday.com that because there are fewer airplanes flying now that the accuracy of weather forecasts may not be as good as otherwise. In such a case, I wish your temperature lows will be in the 34-35 range instead! So you get rain and no snow!