Definition of Compost
Knowing what compost is (and what it’s not) is an important first step in ensuring that you use compost in the best way possible. Below is the official definition for what can be considered compost.
Compost - is the product manufactured through the controlled aerobic, biological decomposition of biodegradable materials. The product has undergone mesophilic and thermophilic temperatures, which significantly
reduces the viability of pathogens and weed seeds (in accordance with EPA 40 CFR 503 standards) and stabilizes the carbon such that it is beneficial to plant growth. Compost is typically used as a soil amendment, but may also contribute plant nutrients.
(AAPFCO definition, official 2018) Finished compost is typically screened to reduce its particle size, to improve soil incorporation.
Do you wonder how the definition of compost was formed? Here is background on the USCC's definition of compost.
Related and Allowable Products
- Vermicompost/Worm castings for which all feedstocks have been composted prior to it utilized as worm bedding or feed, and the final product meets EPA 40 CFR 503 standards;
- Digested solids (materials anaerobically digested) that have been composted after removal from the digester and which the final product meets EPA 40 CFR 503 standards; or
- Any other substance that undergoes composting and is similar to Compost Product(s) in appearance, application and performance may apply to be considered by the STA Advisory Committee on a case by case basis.
These products may be registered as either standard STA products, or derivatives of STA products, depending on their manufacturing process.
- Composted Mulch – Compost of a coarser particle size, containing a larger percentage of composted wood particles, and that meets the STA Program rules.The product is commonly used on the surface of the soil.
- Erosion Control Compost – Compost of a coarser particle size, containing a larger percentage of composted wood particles, and that meets the STA Program rules, and meets user defined specifications related to particle size distribution.The
product is commonly used as an erosion control blanket, berm, or sock media.
- Soil Remediation / Stormwater Management Compost – Compost of a coarser particle size, containing a larger percentage of composted wood particles, and that meets the STA Program rules, and meets user defined specifications related to particle
size distribution.The product is commonly used in soil incorporation in soil remediation and stormwater management applications.
Separate compost products are defined as being any one of the below:
- Created at separate facilities - Material created at different facilities, all with the same name, is not just one product. They should be registered as multiple products, one per facility.
- Created with different feedstocks - If you use the same feedstocks, in the same ratios, at the same facility, that should be registered as one product. Even if only one feedstock is different, that should be registered as a separate product.
Derivative products are defined as being STA Certified Compost products that are then changed in any one of the ways below, which do not get re-tested
and do not get a new Compost Technical Data Sheet (CTDS):
- Re-named - The product's the same, but you or someone else want to distribute it under a different name.
- Screened - The product's the same, but you've changed the sieve size. Coarse derivative products are acceptable, but the originating compost product must be composted enough to match our definition of compost.
- Blends/Mixes - When sand, mulch, potting soil, or another substance are blended or mixed into your compost product. Must contain at least 25% of your compost product or it cannot be in the program. (Registrations for this type of derivative are paused in 2021 for re-evaluation)
Un-Composted Mulch
cannot be registered. A registered compost may be screened to create coarse mulch-like material as a derivative product, but it must match our definition of compost prior to screening.
