What can I put around young trees that the grass doesn't grow always back too close to the little trunk?

-?Mulch is fine, except don't pile it up against the trunk, thin it out right there, like a little bowl. Main thing is not to bang into it with a lawn mower or line trimmer.Treated mulch, stones,
Spray around the base of the tree with Roundup.
thick layers of newspapers and you make a collar aroundd the tree