Pine tree mulch bed

[Family man]

I have several medium sized pine trees growing in my yard. There is currently grass growing all around them but I would like to make it into a mulch bed where I could put grass clippings and other yard debris which would also make it much easier to mow around. I do not want to put up any kind of border around the bed as it will be rather large so I was planning on just digging a small trench around the area to act as a border. I also do not want to put down landscaping cloth because of the large area. My main questions are: do I need to kill the existing grass in the bed or will it just die as it gets buried with grass clippings (if I do need to kill the grass what is the best way to do that - Roud up)? Also, do grass clippings make for a good mulch for pines or do I need to add additional types of mulch?

[email protected]

 

[treeseer]

I was planning on just digging a small trench around the area to act as a border.
Make it shallow or you may damage too many roots.

do I need to kill the existing grass in the bed or will it just die as it gets buried with grass clippings (if I do need to kill the grass what is the best way to do that - Roud up)?
Some grasses will smother ok, rhizomatous sp--bermuda and others with "runners"--will colonize the mulch. Roundup's ok but beware spray drift onto your pines. Better to use Grass-B-Gone, or Poast on grass around trees.

Also, do grass clippings make for a good mulch for pines or do I need to add additional types of mulch?
Yes these are high in nitrogen, but if ftoo thick they mat and put out bad fumes. Thin layers with pine bark mixed?

ps if you keep the lower branches on your pines their shade will suppress weeds.