Hardy down to -5 deg C - suppose you could try wrapping fleece, might help. It'd survive most winters - but not the last or the one before. If you choose your planting site carefully, making it sheltered and out of north easterly winds and not in a frost pocket, that would help.

A well drained soil helps borderline hardy plants as well

Thanks for the info, i think i will lift them in late autumn & overwinter in greenhouse derekm

I am experimenting with plants I need to lift by planting them within plastic pots with the bottoms cut off. This minimises root disturbance when they are lifted

Seems like a good idea, but i don,t have any borders in my greenhouse, so i would have to repot them anyway into pots with bottoms intact. good luck with yours.derekm

I just stand the lifted pot inside another one

Thank,s Andrewr, funny how the simple solutions never occur to you isn,t it, lol