Certainly the tender ones do need protection. I always take cuttings in mid/late summer as an insurance of a hard winter. Some don't survive in the greenhouse if it dips below 0c for several days. I keep them on the dryish side too in the greenhouse as it is often wet and cold rather than cold that does it in for them.

Thanks for your replies.
I think I'll dig them up and put them in a friend's glass greenhouse as mine's plastic, then that way they'll sure to survive by spring.

they may still not survive if they've already been badly frosted. but fingers crossed.

Sorry to hijack this Irridium but I'm very interested in what SBG has to say. I've been bringing my cuttings indoors when The forecast is very cold. My coldframe doesn't inspire me with confidence and it is plastic like your greenhouse. I must say that some of the cuttings are not doing well while the bog sage( can't remember its proper name) is still doing ok outside and not so well as a cutting. My salvia amisted is doing great as a cutting. Thankyou SBG for the info.