Kind of up to you. I cut back Red hot poker as the stem rots if you do not, and Gypsophilia as it self seeds, but leave Sea Holly as I like the shape over winter. It does look battered by spring so as I said it is up to you - if you like it then keep it, if you want it clear then cut them after they turn from green.

thanks very much

I agree with Kildermorie 100% (rare on a gardening forum - lol). I have 3 different Echinops and all look wonderful in winter with frost or snow on.

I've just posted a photo of how I overwinter my red hot pokers. In the Spring I'll untie them and take away any dead or damaged foliage. I add the leaves etc to my compost bins. They help make excellent compost. I remove any slug I find when I'm tying them up and have never had any bother with slugs on them.