Its borderline tender/hardy, but I've never had one make it through a winter. You could try moving it somewhere frost free over winter.

Hello! Once first frosts have bitten off the top of the plant, lift tubers and store somewhere above freezing, i.e. cool and dry. It's a bit like over-wintering dahlias ... put tubers in pot of multi-purpose compost somewhere where temperatures won't drop below freezing, then plant out again in April/May when hard frosts are over, which may be April as you are south. Hope this helps.

I find this plant is more tender than Dahlias. I leave them in the ground, but chocolate cosmos pegged out every winter I've tried it.

Jeanette, I'm in West Somerset, and much to my astonishment, my Cosmos came through last winter. I can't imagine how it managed to survive, but it did. I'm certain that you need to take the advice above to be safe, though.

wow!! I am amazed by your quick responses everyone, thanx so much for your advice!!
I will try moving to frost-free in pots of muti-purpose compost..since this means my shed, does this mean I should protect with fleece too??
Funny they haven't survived in london and cornwall..but they have in west somerset..much closer to me!!(maybe hope for mine yet??!!)
shame julia, love these plants - I'm fine thank you, hope all ok with you and yours x
one more thing..this one has gone over quite quickly this week - no rain(!) and lack of attention to detail by me(!) does this hold out hope that the plant is still alive where it matters??
thanks everybody! :-)

Yes, and if you pot it up and keep it frost free, I'm sure it'll be OK. Good luck!

thanx spritz, that's a job for today then since it's a lovely sunny day (at the moment!!) :-)

Dress up warm - the wind is really cold!

I retrieved the above-mentioned Cosmos from its cosy fleece wrapped billet in the shed last week..since then we've had a couple of frosts!! No sign of any life, level compost surface at the moment, have left it in the shelter of a wall since I brought it 'outdoors'! I was just wondering how long before I will see signs of life - if its goin to happen at all!! thanx all :-)

It came out just in time for some cold weather!

I know Beattie!! and it had been so warm for the previous week..hope I haven't lost it after the effort I made to keep it thru the winter.. :-)