California Department of Resources Recycling and Recovery (CalRecycle) 

Purchasing Compost & Mulch

Writing Mulch & Compost Specifications: Examples

Example: Mulch specification for use in public works application

"Greenbook" Standard Specifications for Public Works Construction
American Public Works Association, Southern Calif. Chapter (
Contact: Kristen Aston, Chapter Administrator, (714) 639-1374

"When mulch without further specification is specified, the contractor shall supply Type (A) or Type (B) mulch. Type 12(A) mulch (1" minus in size) and 12(B) mulch (4" minus in size) shall be clean green material that is processed in accordance with California Code of Regulations, Title 14, Chapter 3, Article 7, Section 17868.3, to promote pathogen reduction and weed seed kill. A 3-inch minimum layer of type 12(A) or 12(B) is required for all applications. Type (B) mulch should be used on slopes that are a maximum of 50 degrees (2:1)"

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Example: Compost specification for erosion control

Interim CalTrans Specification for Compost
Contact: California Department of Transportation
Engineering Service Center  (916) 227-7289

Compost shall be derived from green material consisting of chipped, shredded, or ground vegetation or clean, processed, recycled wood products or a Class A, exceptional quality biosolids composts, as required by the United States Environmental Protection Agency (EPA), 40 CFR, Part 503c regulations or a combination of green material and biosolids compost. The compost shall be processed or completed to reduce weed seeds, pathogens, and deleterious material, and shall not contain paint, petroleum products, herbicides, fungicides, or other chemical residues that would be harmful to plant or animal life. Other deleterious material, plastic, glass, metal, or rocks shall not exceed 0.1 percent by weight or volume.

A minimum internal temperature of 57°C shall be maintained for at least 15 continuous days during the composting process. The compost shall be thoroughly turned a minimum of 5 times during the composting process and shall go through a minimum 90-day curing period after the 15-day thermophilic compost process has been completed. Compost shall be screened through a maximum 9.5-mm screen.

The moisture content of the compost shall not exceed 35 percent. Compost products with a higher moisture content may be used provided the weight of the compost is increased to equal the compost with a moisture content of 35–40 percent. Moist samples of compost on an as-received basis shall be dried in an oven at a temperature between 105°C and 115°C until a constant dry weight of the sample is achieved. The percentage of moisture will be determined by dividing the dry weight of the sample by the moist weight of the sample and then multiplying by 100. Compost will be tested for maturity and stability with a Solvita test kit. The compost shall measure a minimum of 6 on the maturity and stability scale.

Note: The screen size and the maturity/stability measurement may change, depending on the intended use of the compost.

Procurement Specifications Guidelines

Last updated: September 19, 2013
Organic Materials Management