Is it okay to put mulch around a 20 year old tree?

Question

Or will it kill it because the roots are covered?

Answer 1

Mulch is fine.  Just keep it away from the trunk.  It is additional soil that can smother a tree.

Answer 2

If the roots are exposed and on the surface, the mulch will not hurt nor help a tree that age. It would end up washing away. I'd save the mulch and the energy for better purposes. Mulch would retain moisture, encouraging more surface growth, something not desirable.

Answer 3

it is advisable.  but do not pile up the mulch against the trunk, or form a volcano.  a mulch ring should start close to the trunk, and go as far as the drip line if you have enough.  it should be 2-3" deep and cover the tree well/basin to hold rainwater.  the roots can breathe through it