how do you know when half-hardy plants are dead?

[CurlyhairedAssassin]

I had some argyranthemums in a big pot last summer with some other stuff that seems to be growing back, and didn't realise they should be protected from frost. I've cut off all the woody stems but I can't see anything new at the base. I dug one up and the roots still look a bit "juicy". there seems to be the tiniest bit of green at the top of one if I peel at it. Do you think they'll grow back?

The one I dug up I put back in the soil but not sure it'll appreciate that and if it had any life in it at all I've probably finished it off!

I'd give it until about end May beofre declaring it totally dead.

Thanks. I've left them in. I've also got an erisymum that was a tiny plug plant last year and I just potted on to a bigger pot. It looks like it could be dead but there is a weeny bit of what could be green colour at the base. So I've got the moss out, top dressed it, put some fertiliser in and given it a good water, so fingers crossed that will show signs of life soon too.