deep beds of grass clippings

Problem with heaped grass clippings is they quickly rot to a soggy rotten mess, nothing conducive to good plant growth. Just use it for mulching for now. For planting, dig out a planting circle and set the plants into the soil but don't pull the clippings back just yet. Plant stems need to be older growth to deal with clippings.

Excellent point. So many lawns are sprayed heavily.

not really helping with your question but my dad now mixes grass cuttings with leaves (whole ones, not shredded) in roughly a 50/ 50 mix by volume.

piles into a black bag (he uses inside out compost bags) and ties the ends up with string.

then piles them up and leaves to rot down he moves the pile every 3 or 4 months, this puts the top of the pile to the bottom and visa versa. he also gives them a bit of shake and move about while he does this.

after a year it makes blooming good compost with minimal effort imo.

if there is a chance of plants being burnt by the composting grass clippings how about larg plastic pots with the bottoms cut of then pull the compost back and push these in to the ground then plant or sow within the perimeter of the pots ?

That'd would work but it's extra work then you'd have the bother of disposing of the pots later on. Simply keeping the grass away from new plants would work just as well.

I have used grass clipping for quite a while to cover newly emerged potatoes to protect them from early frost. Light layers of clippings do give warmth but too thick a layer will (as has been said) form a heavy decaying mat... not at all useful.

Grass helps add organic material but I doubt if it adds nitrogen to the soil - probably the reverse if it decays on the surface rather than in a mixed compost heap.

Mulch around established plants with it, when it dries out in the summer fork it in. I add it over a sprinkling of pelleted chicken manure (slow release fertiliser).