Can I use this winters cow muck as a starting mulch on the grass I want to kill off under the proposed veg garden, or does the muck used need to be well rotten? Any help please.
Go ahead. Put down 15cm thick, and cover paths at the same time, pull any weeds that come through, take care of the edges and it will be ready next spring, though it will already be ready in summer for plantings and in fall for sowing.