Two to 3 inches of mulch is right for most beds. Less does not block weeds well, and more can smother roots.
Depth by use
Flower beds: 2 to 3 inches. Vegetable gardens: 1 to 2 inches of finer material. Tree rings: 2 to 4 inches, kept back from the trunk. Paths: 3 to 4 inches. Play areas: follow equipment and safety guidance, often 6 to 12 inches.
Why not too deep
A thick layer holds water against the stems, invites pests, and limits air to the roots. Volcano mulching, where mulch is piled up around a trunk, shortens the life of many trees.
Cubic yards by depth
For 100 square feet, 2 inches needs 0.62 cubic yards, 3 inches needs 0.93, and 4 inches needs 1.23. Add 10 percent to cover settling.
Refreshing
Rake last year mulch to loosen it, and add about an inch to bring the depth back up. Remove old mulch only when it is matted or more than 3 or 4 inches.
Frequently asked questions
How thick should mulch be around trees?
About 2 to 4 inches, pulled back a few inches from the trunk.
Can mulch be too thin?
Under 2 inches, weeds often come through.
How often should I add mulch?
Commonly once a year, as a thin top up.