Posted: 27/02/2014 at 21:57
Hi Bex - this has happened to me before with Cosmos - they go a bit wild! So I now wait til March to sow, don't give them any heat (just a light windowsill) and prick them out, with quite a lot of the stem below the compost.
if you want to attempt to rescue the ones you have now, i would try planting them up individually, but you will need to plant them deeply to stop them keeling over. And keep them off the heat