How much mulch around a tree
A mulch ring is a circle with a smaller circle left bare at the trunk, so its area is π/4 × (outside² − inside²). A ring 6 feet across with a 1 foot bare circle at the trunk is π/4 × (36 − 1) = 27.5 square feet. At 3 inches deep that is 6.9 cubic feet; with 10% for spill and settling, 7.6. In 2 cubic foot bags you buy 4 bags, or 3 of 3 cubic feet.
Choose the ring shape and give it the two diameters a tape measures: across the whole ring, and across the bare circle around the trunk. The bare circle is the point of the shape. Calculators that only take a plain circle charge you for mulch piled against the bark — the one place it should not go.
Keep it off the trunk
The University of Illinois Extension recommends 2 to 4 inches of mulch, and keeping it away from the trunk. Mulch heaped against the bark — the "mulch volcano" — keeps the bark wet. Make the inside diameter the trunk plus a few inches all round, and the page leaves that circle out of the order.
Type a depth outside 2 to 4 inches and the ring says so beside its depth box.
Rings by size
| Ring across | Mulched area | At 3 in, with waste | 2 ft³ bags |
|---|---|---|---|
| 4 ft | 11.8 ft² | 3.2 ft³ | 2 |
| 6 ft | 27.5 ft² | 7.6 ft³ | 4 |
| 8 ft | 49.5 ft² | 13.6 ft³ | 7 |
| 10 ft | 77.8 ft² | 21.4 ft³ | 11 |
Each with a 1 foot bare circle at the trunk. A larger trunk leaves a larger circle bare; type its own diameter.
Several trees
Trees of the same size are one ring with a quantity: three 6 foot rings are the quantity 3, 22.7 cubic feet with waste, and 12 bags of 2 cubic feet. The page adds the rings up before it rounds to whole bags, so the part of a bag one ring leaves over is not bought again at the next. Trees of different sizes are one ring each; add a ring for each. A bed around a group of trees is a rectangle or another shape, with a circle subtracted for each trunk.
Buying it
A few rings are a few bags: 4 bags of 2 cubic feet weigh about 140 lb at the EPA's figure for moist wood chips, 473 lb a cubic yard. Every bag size is worked out in the bag table; the cheapest mix appears once you type the prices. If the rings are part of a larger job — a whole bed, a row of trees along a drive — a delivered load starts to pay from about 2 cubic yards, and the comparison under the shopping list says from where. We are not connected with any store or supplier.