How Much Mulch for a Tree Ring? Bags by Ring Size, 4 to 12 ft

A young maple stands in a knee-high cone of mulch, its bark buried. A tree ring 6 feet across (3 ft radius) spread 3 inches deep takes about 6.9 cubic feet: 4 bags of 2 cu ft. An 8 ft ring takes 12.4 cubic feet: 7 bags. Both counts leave the center foot around the trunk bare.

The cone is the part to avoid. University of Illinois Extension says mulch piled against the bark holds moisture there, so the bark starts to rot, and the rot can reach the cambium and kill the tree. It also invites voles and mice to chew the bark. The chart below keeps mulch flat and off the trunk.

Free calculator: our free mulch calculator turns ring size and depth into cubic feet, yards and bags. No sign-up.

How many bags of mulch for a tree ring

Each ring leaves the center 1 ft across bare (the trunk plus a gap). Bag counts are rounded up.

4 ft ring (2 ft radius), 2 in — 2.0 cu ft; 1 bag (2 cu ft) or 1 bag (3 cu ft)

4 ft ring, 3 in — 2.9 cu ft; 2 bags or 1 bag

6 ft ring (3 ft radius), 2 in — 4.6 cu ft; 3 bags or 2 bags

6 ft ring, 3 in — 6.9 cu ft; 4 bags or 3 bags

8 ft ring (4 ft radius), 2 in — 8.3 cu ft; 5 bags or 3 bags

8 ft ring, 3 in — 12.4 cu ft; 7 bags or 5 bags

10 ft ring (5 ft radius), 2 in — 13.0 cu ft; 7 bags or 5 bags

10 ft ring, 3 in — 19.4 cu ft; 10 bags or 7 bags

12 ft ring (6 ft radius), 2 in — 18.7 cu ft; 10 bags or 7 bags

12 ft ring, 3 in — 28.1 cu ft; 15 bags or 10 bags

Mulching several trees? Five 6 ft rings at 3 inches come to 34.4 cu ft, about 1.3 cubic yards: 18 bags of 2 cu ft. Past a yard or so, compare the price of bulk. See how many bags of mulch in a yard.

How to measure a tree ring

Radius: half the ring's width, from the trunk to the outer edge.

How wide: Illinois Extension says to make the ring as wide as possible or practical, and ideally to mulch out to the dripline, the edge of the branches.

Area: 3.14 × (radius × radius − 0.25). The 0.25 takes out the bare center 1 ft across. A 3 ft radius is 3.14 × 8.75 = 27.5 sq ft.

Volume: square feet × depth in inches ÷ 12 = cubic feet. Divide by 2 for 2 cu ft bags, or by 27 for cubic yards.

How to mulch around a tree

Leave a gap. Illinois Extension says to leave a two-inch gap between the trunk and the ring of mulch.

Keep it 2 to 3 inches deep. Illinois Extension says 2 to 4 inches. The University of Maryland Extension says mulch should be three inches or less, since deeper mulch can rob roots of water and encourage shallow rooting.

Top up, don't stack. Push a finger into the old ring and measure what is left. Only add the difference, so the total stays at 3 inches or less.

Allow for settling. Fresh mulch settles. When it has, add 1 to 2 inches to bring it back to about 3.

Free option: shredded leaves. See how to turn fall leaves into free mulch.

Not a fit: a mound that touches the bark, at any depth. Pull it back to a flat ring first, then fill with the counts above.

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Tree ring mulch FAQ

How many bags of mulch do I need for one tree? For a 6 ft ring, 4 bags of 2 cu ft at 3 inches, or 3 bags at 2 inches. An 8 ft ring takes 7 bags at 3 inches.

How far from the trunk should mulch be? Illinois Extension says to leave a two-inch gap between the trunk and the mulch, so the bark stays dry.

How deep should mulch be around a tree? Illinois Extension says 2 to 4 inches, and the University of Maryland Extension says three inches or less. Two to 3 inches meets both.

How big should a mulch ring around a tree be? As wide as practical. Illinois Extension says to mulch out to the dripline if you can.

Why is volcano mulch bad? Illinois Extension says mulch against the bark holds moisture that rots the bark and can reach the cambium, which can kill the tree. It also draws voles and mice.

Free calculator: pick Tree ring in the free mulch calculator, enter the outer diameter and leave trunk diameter at 1 ft to match this chart.

Watch Curb Calc on YouTube: youtube.com/@curbcalc

Sources: University of Illinois Extension, Volcano Mulch (A Merry Gardener); University of Maryland Extension, Home Landscape Best Management Practices.