Posted: 24/02/2014 at 21:23
Well, the iron sulphate won't harm anything but I'd be a bit wary of any spores from fruiting bodies within the dead moss causing moss to grow where it is used as a mulch. Personally, I'd have no qualms about adding it to a compost heap though, where the bacteria and worms will 'eat' any spores. Then use the compost as a mulch.
Edit: I didn't see Dove's post until after posting my reply and am a bit perplexed why that site says not to put it on the compost heap. While I'd not put rakings on after using feed & weed, FeSO4 is pretty harmless. I'll do a bit of research.