Help! Frost has killed my dahlias

An unexpected sub zero temperature overnight in Essex has killed (?) my dahlias which had been hardened off outside, both new tubers and old ones from last year. Is there anything I can do to help these? Will they be complete gon-ers? This is only my second year growing dahlias so a bit clueless!"

 

They should re shoot when ALL chance of frosts have gone

 

The weather this year has been a total arse...hope they resprout for you.

 

It really has been bad! Normally last chance of frost here is mid April - I have been keeping an eye on things and moving some stuff inside initially when it was around 3 or 4 overnight, but it wasn't forecast to be sub zero last night and I got caught out! A lot of my seedlings have frost damage too :(

I really hope they do reshoot, thank you @flounder

 

They probably aren’t dead, and will just have been knocked back a bit. Important to avoid it happening again this season.

 

My rough rule of thumb re putting dahlias outside is this. If it’s good enough for tomato plants to go out, it’s okay for the dahlias too. Unless you had a very deep frost, I suspect the cold will have only nipped the green growth and the tubers will be ok. Move them to a greenhouse/somewhere sheltered and fleece if necessary. They will most likely re-sprout in due course. I take cutttings from my dahlias and for each sprout I take off, 4 more will eventually grow.

 

I agree with @Ezzie . Dahlias aren't hardy, so they need the same treatment as any other half hardy plant. The tomato comparison is a good one.
Mine really have to be overwintered in the house. The shed isn't watertight, and it's the wet cold that's a real killer for them. Growhouse is nowhere near warm enough either, even with the mild winters we've been getting here recently.
A couple of mine are sprouting, so they're in the growhouse, inside another clear box. I move them around according to how they're doing.
I think those will be ok, as the others have said, once the temps rise again. I agree that it'll only be the main new growth that's damaged. If it was persistently wet and cold that would be more harmful.