How deep should mulch be?
Two to four inches. University of Illinois Extension gives 2 to 3 in for fine, composted mulch and 3 to 4 in for coarse bark and wood chips. More is not better: a thick layer mats, and water and air stop reaching the roots.
| For | Depth | In metric |
|---|---|---|
| Fine, composted mulch | 2 in | 5 cm |
| Most beds | 3 in | 7.5 cm |
| Coarse bark and wood chips | 4 in | 10 cm |
University of Illinois Extension: The recommended mulch depth is 2 to 4 in: composted materials 2 to 3 in, coarse mulches 3 to 4 in. Keep mulch at least 4 in away from the trunk.
Scotts: Sold in 1.5 cu ft bags. Spread 3 in deep and keep it several inches from tree trunks.
Keep it off trunks and stems. The same guide asks for at least 4 in of bare ground around a trunk: mulch piled against bark keeps it wet, and rot and insects follow.
Bags or bulk?
Mulch is sold by volume, so there is no density to guess: one cubic yard is 13.5 bags of 2 cu ft, or 9 bags of 3 cu ft.
Worked example. 200 sq ft of beds, 3 in deep.
- Volume: 200 sq ft × 0.25 ft = 50 cu ft = 1.85 cubic yards
- In bags: 25 bags of 2 cu ft, or 17 bags of 3 cu ft
- In bulk: sold by the quarter yard, so order 2 cubic yards
The rule on many bags gives the same: square feet × inches ÷ 324 = cubic yards.
Several beds add up before anything is rounded: the bags are counted once, on the total. Weight matters only for hauling: a supplier puts a cubic yard of shredded hardwood at 500 to 600 lb.
Coverage table
What one bag, and one cubic yard, covers at each depth:
| Square feet covered by | at 2 in | at 3 in | at 4 in |
|---|---|---|---|
| A 2 cu ft bag | 12 | 8 | 6 |
| A 3 cu ft bag | 18 | 12 | 9 |
| One cubic yard | 162 | 108 | 81 |
Topping up old mulch
Measure what is left before you buy. Tick “Topping up old mulch”, enter the depth still in place, and only the difference is counted: the 200 sq ft above, with 1 in of old mulch under it, needs 33.33 cu ft, or 17 bags of 2 cu ft, in place of 25.
Old mulch can usually stay. Scotts suggests loosening it first so that water gets through, and taking some away where the layer is already more than 4 in.
A ring around a tree
Choose the ring shape and enter two diameters: the outside of the mulch and the bare circle around the trunk. A ring 6 ft across with 1 ft left open is 27.49 sq ft. At 3 in deep that is 6.87 cu ft: 4 bags of 2 cu ft.
Rubber mulch
Rubber mulch comes by the bag, most often 0.8 cu ft. What a bag covers is its volume divided by the depth: at 2 in, 4.8 sq ft. Choose “Rubber mulch” as the material and the same 200 sq ft, at 2 in, is 42 bags. Under play equipment the depth comes from the maker of the equipment, not from a bed chart.
Questions about mulch
How many bags of mulch in a yard?
13.5 bags of 2 cu ft, or 9 bags of 3 cu ft. A cubic yard is 27 cu ft: divide 27 by the size on the bag.
How much does a bag of mulch cover?
A 2 cu ft bag covers 12 sq ft at 2 in deep and 8 sq ft at 3 in. A 3 cu ft bag covers 18 and 12 sq ft.
How much mulch around a tree?
For a ring 6 ft across, 3 in deep, with 1 ft left open around the trunk: 4 bags of 2 cu ft. Keep the mulch at least 4 in off the trunk.
Should I remove old mulch?
Not as a rule: it breaks down into the soil. Loosen it, measure its depth and top it up to 2 to 4 in in all. Take some out when the layer is already deeper than 4 in.
Sources
- Sands & Soils, Triple Shredded Hardwood Mulch. A cubic yard of triple shredded hardwood mulch weighs approximately 500 to 600 lb. Read on .
- University of Illinois Extension, Proper Mulching Techniques. The recommended mulch depth is 2 to 4 in: composted materials 2 to 3 in, coarse mulches 3 to 4 in. Keep mulch at least 4 in away from the trunk. Read on .
- Scotts, Nature Scapes Color Enhanced Mulch, 1.5 cu ft. Sold in 1.5 cu ft bags. Spread 3 in deep and keep it several inches from tree trunks. Read on .
Updated . How we calculate. Found a mistake? Tell us.