Types of Mulch Compared
Mulches are organic, such as bark, wood chips and pine straw, or inorganic, such as river rock, pea gravel and rubber chips: Iowa State Extension says organic mulches decompose at different rates, and that inorganic mulches do not improve soil fertility or soil structure.
Estimates for planning, not professional advice. Read the full notice.
Work it out for your own sizes
Size your own bedExample to try: Length 10 ft, Width 10 ft, Depth 3 in
Depth by type of mulch, with the yards for a bed
The depth an extension source gives for each type of mulch, and the cubic yards that depth makes for the example bed
| Type of mulch and source | Depth from | Depth to | Cubic yards at the shallower depth | Cubic yards at the deeper depth |
|---|---|---|---|---|
| Wood chips or shredded bark, well-drained site (Iowa State) | 3 in | 4 in | 0.93 yd³ | 1.23 yd³ |
| Wood chips or shredded bark, heavy soil (Iowa State) | 2 in | 3 in | 0.62 yd³ | 0.93 yd³ |
| Wood chips (University of Maryland) | 1 in | 3 in | 0.31 yd³ | 0.93 yd³ |
| Fine wood and bark mulches, upper limit (Clemson) | 2 in | 3 in | 0.62 yd³ | 0.93 yd³ |
| Cocoa bean shells (Iowa State) | 1 in | 2 in | 0.31 yd³ | 0.62 yd³ |
Estimate for planning, from what you entered and the product data shown. Check product labels and your supplier before you buy.
Cubic yards are the example bed's area times each depth, before any waste allowance. For fine wood and bark mulches Clemson gives an upper limit, shown here as the range it states.
Types of mulch with one depth limit
Mulch types whose source gives a single limit instead of a range, and the cubic yards that depth makes for the example bed
| Type of mulch and source | Deepest layer the source gives | Cubic yards at that depth |
|---|---|---|
| Fresh sawdust, or less (Iowa State) | 1 in | 0.31 yd³ |
| Coarse mulches such as pine bark nuggets (Clemson) | 4 in | 1.23 yd³ |
Iowa State gives sawdust as a thin layer of this depth or less when it is fresh; Clemson gives coarse mulches such as pine bark nuggets as able to go this deep.
Organic mulches
- Bark: slow to decompose, with cedar and cypress the slowest, as Iowa State Extension puts it.
- Grass clippings: they decompose quickly.
- Pine needles, also called pine straw: slow to decompose, and they last several years.
- Cocoa bean shells: they typically last about one growing season.
- Hardwood bark, straw and sawdust: a high carbon-to-nitrogen ratio, which can deplete the nitrogen in the soil.
Available in bags or bulk, bark mulch comes in various particle sizes, ranging from fine to large chunks. Some are colored/dyed for decorative purposes. They are attractive, weed-free, and slow to decompose; cedar and cypress are the slowest.
Grass clippings decompose quickly, making them ideal for vegetable gardens and annual flower beds.
Pine needle mulch, or pine straw, is light, airy, slow to decompose, and attractive. It lasts several years and can be easily removed if necessary.
Cocoa bean shells are excellent mulches for annuals, large containers, perennials, vegetable gardens, and roses. They typically last about one growing season.
Mulches with a high carbon-to-nitrogen (C:N) ratio, such as hardwood bark, ground wood pallets, straw, and sawdust, stimulate microbial growth, which depletes available nitrogen in the soil, potentially causing nitrogen deficiency in plants.
Inorganic mulches
Iowa State Extension names these as the common inorganic mulches, and says what they do and do not do for a bed.
Common inorganic mulches include: ... river rock ... lava rock ... pea gravel ... crushed brick ... limestone gravel ... caramel rock ... rubber chips ... woven landscape fabric ... plastic sheeting
Inorganic mulches do not improve soil fertility or soil structure. Most warm the soil quickly in spring and help retain warmth in fall, but they can keep soils excessively warm during summer.
While inorganic mulches suppress weeds for several years, organic matter and soil gradually accumulate on top, eventually allowing weeds to establish.
Where the sources give no depth
The extension sources opened for this page give no depth for straw, pine straw, stone or rubber mulch, so none is shown. Check the product's label or ask the supplier, then enter that depth in the calculator. Depth by source, without the types, is on the mulch depth chart.
Questions
What are the types of mulch?
Iowa State Extension lists organic mulches (bark, wood chips, leaves, grass clippings, straw, newspaper and cardboard, cocoa bean shells, pine needles, sawdust, compost and leaf mold) and inorganic mulches (river rock, lava rock, pea gravel, crushed brick, limestone gravel, rubber chips, landscape fabric and plastic sheeting).
What is the difference between organic and inorganic mulch?
Iowa State Extension says inorganic mulches do not improve soil fertility or soil structure and can keep soil excessively warm in summer, while its organic mulches decompose at rates that run from quick, for grass clippings, to slow, for bark and pine needles.
How deep does each type of mulch go?
The first table gives the depth each extension source states and the cubic yards it makes for the example bed. The sources opened give no depth for straw, pine straw, stone or rubber mulch.
Which mulch lasts longest?
No source opened gives a comparison in years. Iowa State Extension says pine needle mulch lasts several years, that cedar and cypress are the slowest of the barks to decompose, and that cocoa bean shells typically last about one growing season.
Calculate it for your project
Enter your own sizes to get the amount to buy or the layout figures, with the working shown and a page to print.
Try your own bed in the mulch calculatorSources (4)
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How deep should the mulch layer be around trees and shrubs? (Yard and Garden FAQ) (opens in new tab), Iowa State University Extension and Outreach, last updated March 3, 2022.
Code or government.
“A 3- to 4-inch-layer of wood chips or shredded bark would be appropriate for well-drained sites around trees and shrubs. On heavy soils, a 2- to 3-inch-layer would be suitable.”
Checked November 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 1) -
Mulching Trees and Shrubs (opens in new tab), University of Maryland Extension, updated December 6, 2023.
Code or government.
“Always keep mulch shallow, from one to three inches. Keep mulch about 3 inches away from the base of tree trunks. ... Apply wood chips 1-3 inches deep and sawdust 1 inch deep.”
Checked November 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 2) -
Mulch (HGIC 1604) (opens in new tab), Clemson Cooperative Extension, Home & Garden Information Center, revised June 20, 2016.
Code or government.
“Many wood and bark mulches are composed of fine particles and should not be more than 2 to 3 inches deep. ... Coarse-textured mulches such as pine bark nuggets ... can be as deep as 4 inches. ... One cubic yard will cover a 324-square-foot area with an inch of mulch.”
Checked November 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 3) -
Using Mulch in the Garden (opens in new tab), Iowa State University Extension and Outreach (Yard and Garden), last reviewed February 2026.
Code or government.
“Available in bags or bulk, bark mulch comes in various particle sizes, ranging from fine to large chunks. Some are colored/dyed for decorative purposes. They are attractive, weed-free, and slow to decompose; cedar and cypress are the slowest.”
“Grass clippings decompose quickly, making them ideal for vegetable gardens and annual flower beds.”
“Pine needle mulch, or pine straw, is light, airy, slow to decompose, and attractive. It lasts several years and can be easily removed if necessary.”
“Cocoa bean shells (also called cocoa hulls) are a by-product of chocolate production ... a depth of 1 to 2 inches is sufficient.”
“Cocoa bean shells are excellent mulches for annuals, large containers, perennials, vegetable gardens, and roses. They typically last about one growing season.”
“Mulches with a high carbon-to-nitrogen (C:N) ratio, such as hardwood bark, ground wood pallets, straw, and sawdust, stimulate microbial growth, which depletes available nitrogen in the soil, potentially causing nitrogen deficiency in plants.”
“Common inorganic mulches include: ... river rock ... lava rock ... pea gravel ... crushed brick ... limestone gravel ... caramel rock ... rubber chips ... woven landscape fabric ... plastic sheeting”
“Inorganic mulches do not improve soil fertility or soil structure. Most warm the soil quickly in spring and help retain warmth in fall, but they can keep soils excessively warm during summer.”
“While inorganic mulches suppress weeds for several years, organic matter and soil gradually accumulate on top, eventually allowing weeds to establish.”
“Sawdust is easy to apply, weed-free, and decomposes slowly. Compost or age sawdust for a year before use, or apply a thin layer (1 inch or less) if fresh”
Checked November 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 4)
These are summaries of what the sources say, not professional advice. Codes and product data change. Check with your building department and the product label about your own project.