Don’t make a mulch volcano around trees. Tree experts say it can suffocate the tree. Why? Because it covers the root flare of the tree; the parts of the tree meant to be exposed to air. Mulch the right way. Keep mulch 12 to 18 inches away from the trunk of any tree. Avoid burying the root flare (the base of the tree emerging from the soil). Spread mulch only 2 to 4 inches thick. Learn the best way to plant trees.