The short answer
Spread mulch 2 to 4 inches deep on beds and around trees, as the University of Minnesota and Penn State Extension both give, and keep it off tree trunks. Penn State adds: no more than 4 inches, and less where the soil drains poorly.
Depth by use
| Where | Depth | Source |
|---|---|---|
| Beds and borders | 2 to 4 in | University of Minnesota Extension |
| Around trees | 2 to 4 in, no more; less on poorly drained soil | Penn State Extension |
| Paths and high-traffic areas | 3 to 4 in of coarse mulch such as wood chips | NC State Extension |
| Inside vegetable plots | 1 to 2 in of finer mulch such as leaves or straw | NC State Extension |
| Top of a raised bed | Leave 1 to 2 in of space below the rim for it | Iowa State University Extension |
Keep it off trunks and stems
The University of Minnesota Extension says to leave a 6-inch mulch-free ring around tree trunks to avoid root rot and insects. Penn State’s rule of thumb is to pull mulch 3 to 5 inches away from young trees and 8 to 10 inches from mature trees. The mulch calculator has a tree ring shape that leaves that bare circle out.
Mulch calculator
Open the calculatorHow much to order
One cubic yard covers 324 square feet 1 inch deep, or 108 square feet at 3 inches, the University of Florida IFAS Extension says. Per 100 square feet, that is 0.62 cubic yards at 2 inches, 0.93 at 3 inches and 1.23 at 4 inches.
Check what is already on the ground and order only the new layer: if 1 inch remains and you want 3, order 2. The mulch calculator starts the extra at zero, so the amount it gives is what the area and depth take. None of the extension services we cite gives a percentage to add for mulch. The table lists the allowances a state agency, extension services and a maker give for other jobs.
| Job | Extra to order | Source |
|---|---|---|
| Mulch on beds and borders | No figure given; the calculator starts at zero | No published figure |
| Compacted gravel path or base | About 11%: multiply the compacted volume by about 1.11 | Maine Department of Environmental Protection |
| Sod | About 5% to about 10% | Mississippi State University Extension; Purdue Extension |
| Raised-bed soil, for settling | 10% | Frame It All, in its own soil calculator |
Ask your supplier for its figure for the product you buy: how much a material compacts or settles depends on the material.
Try it with your numbers
Put in your own bed and the mulch calculator works out the answer as you type.
Open the mulch calculatorReferences
- Mulching for soil and garden health, University of Minnesota Extension.
- Mulching Landscape Trees, Penn State Extension.
- Soil, Plots, and Planters (AG-806), NC State Extension.
- Creating Raised Bed Planters, Iowa State University Extension and Outreach.
- Choosing and Installing Mulches, University of Florida IFAS Extension.
- Sod Installation and Maintenance, Mississippi State University Extension.
- Establishing a Lawn From Sod, Purdue Extension.
- Gravel Road Maintenance Manual: A Guide for Landowners on Camp and Other Gravel Roads, Maine Department of Environmental Protection.
- Raised Garden Bed Soil Calculator, Frame It All.