I'm wondering how you know the roots are 'lovely and healthy' - presumably, you've potted them into fresh compost and are keeping somewhere inside till they start into growth - they should not be put outside until all risk of frost is past, which is end of May.

Re Chocolate Cosmos.

We treated them as Dalia's and potted them up in the spring, the roots are fleshy and there are fresh shoots on the tubers.
But still no sign of green top growth.

they were kept in a greenhouse all winter(kept above freezing)

Seems odd they're not growing even by now - doesn't look good, does it.

I have now planted them in the ground covered them up and just hoping I am not giving up just yet.

I am not having much luck with choc cosmos I ordered some from Jersey direct on the 5th May and recieved an email today saying they are out of stock.

So now trying another nursery.

Thank-you for your replies.