Reference

Mulch Glossary

Every term we use across the 19-entry glossary below, defined in plain English. Each definition is linked from the calculators and blog posts so the math always traces back to a clear meaning.

Cubic yard: A volume unit equal to 27 cubic feet (about 0.765 cubic meters). In mulch sales it is the standard bulk-delivery unit and covers 108 square feet at a 3-inch depth.
Cubic foot: A volume unit equal to 1,728 cubic inches (about 28.3 liters). Bagged mulch is most often sold in 2 cu ft and 3 cu ft bags; 27 cubic feet equal one cubic yard.
Mulch bag: A pre-packaged plastic-bag unit of mulch sold at retail. The two common sizes are 2 cu ft and 3 cu ft. 13.5 bags of 2 cu ft (or exactly 9 bags of 3 cu ft) equal one cubic yard.
Mulch depth: The vertical thickness of an installed mulch layer, measured in inches or centimeters. Garden guidance varies by plants, material, and site. Playground surfacing must follow the exact product system's ASTM F1292 critical-fall-height documentation, installation instructions, and maintenance depth.
Mulch coverage: The square footage that a given volume of mulch covers at a chosen depth. The working formula is 324 sq ft divided by depth in inches per cubic yard — so 108 sq ft at 3 inches or 162 sq ft at 2 inches.
Mulch: Any material — organic or inorganic — spread on top of soil to retain moisture, suppress weeds, regulate temperature, or improve appearance. Common organic mulches include shredded hardwood, pine bark, cedar, cypress, straw, and wood chips.
Hardwood mulch: Shredded mulch made from hardwood tree species such as oak, maple, or hickory. Cost-efficient and the most common landscape mulch in the United States, with a 1-2 year color lifespan and a 2-3 year breakdown horizon.
Pine bark mulch: Mulch made from the bark of pine trees, sold in nuggets, mini-nuggets, or shredded form. Lasts longer than hardwood (3-4 years), is slightly acidic, and floats in heavy rain.
Cedar mulch: Mulch shredded from cedar wood and bark. Naturally aromatic, mildly pest-repellent, and long-lasting (3-4 years), but more expensive than hardwood.
Rubber mulch: Recycled-tire mulch used primarily in playgrounds and high-traffic landscaping. Long-lasting (10+ years), inorganic, and tested against ASTM F1292 for fall safety at 6-inch depth.
Dyed mulch: Wood mulch colored with iron-oxide (red, brown) or carbon-based (black) pigments. Holds color through the first season but offers no organic benefit beyond the underlying wood.
Compost: Decomposed organic matter used as a soil amendment. Not a true mulch — compost feeds soil biology and is typically tilled in or top-dressed at shallow depths, whereas mulch sits on top to suppress weeds.
ANSI A300: American National Standard for Tree Care Operations. Part 2 covers soil management and mulching practice: a maximum 4-inch mulch depth around trees, with a 2-3 inch dry buffer around the trunk to prevent volcano damage.
ASTM F1292: Standard Specification for Impact Attenuation of Surfacing Materials Within the Use Zone of Playground Equipment. It evaluates head-impact severity and peak acceleration at a tested critical fall height; compliance is tied to the exact surfacing system and its documented installation and maintenance depth.
Mulch volcano: A cone of mulch piled against a tree trunk, often 6-12 inches deep. Causes bark rot, girdling roots, and pest entry. The ANSI A300-compliant fix is to pull mulch back 2-3 inches from the trunk and limit depth to 3 inches at the drip line.
Settling: A change in installed depth as loose mulch compacts, shifts, and decomposes. The amount varies by material, particle size, moisture, traffic, installation, and time; inspect the bed and follow product or supplier guidance instead of assuming a universal percentage.
Top-dressing: Adding a thin (1-inch) refresh layer of mulch on top of an existing aged layer. Restores color and depth without requiring a full re-installation, and is the typical mid-season maintenance action between full applications.
Edge loss: Mulch that ends up beyond the intended bed boundary during spreading. Accounts for a meaningful share of the overall 10% over-order buffer; sharper bed edging and slower wheelbarrow runs reduce it.
Weed suppression: The ability of a mulch layer to block sunlight from reaching weed seeds. Requires a minimum 3-inch depth across the bed; thinner layers admit enough light for weed germination.