I've had some that have happily overwintered a typical no lower than -5 winters, but it tends to be the wet that does for them.
I usually took cuttings as back up. The opens in better draining soil did better, but when growth starts watch out for the gastropods.

Ta!

They seem to be short lived in my garden on Vancouver Island. They produce lots of flowers and it seems to exhaust them.When I cut them really short by this time they sometimes survive. Also, they like lots of sun and our place is mostly shady.I love them, they add lots of cheerfulness to the garden. I treat most of them as annuals.
I also think they do not like our wet winters.

They do well for me, this is the third winter they have come back for me and they have been lovely all summer and still going strong. Fingers crossed. Good luck Owdboggy if you give them a go.

Boughted some seed and sowed half of it to see what happens. Will sow the rest in Spring.