Using STA Certified Compost – Program Foundation: Defining Compost

By Melinda Hamilton | September 20, 2022

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.

 

 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.

New Compost Definition – Results From USCC Work with AAPFCO

The American Association of Plant and Food Control Officials has approved a new definition for compost that emphasizes the pathogen-removing thermophilic process, differentiating it from many products often confused as compost.

“This definition more completely defines what our products are so that people out there wanting to call their products compost cannot do that without meeting this definition,” said Ron Alexander of R. Alexander Associates, the USCC’s liaision to the AAFPCO, who has labored for years on the updated definition language. The new definition was adopted at the group’s winter meeting held in Savannah, GA last week.

The official definition is:

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, 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.

The prior definition was: The biological decomposition of organic matter. It is accomplished by mixing and piling in such a way to promote aerobic and/or anaerobic decay. The process inhibits pathogens, viable weed seeds, and odors. (Official 1997)

“The USCC has been working on quality compost for 25 years, and we don’t want to have the compost industry’s product being confused with other products after all the work we’ve invested in best practices and quality product standards,” said Alexander, who spearheaded the AAPFCO workgroup that has worked for two years on the new definition.

The new definition also helps the makers of other products, from biochar to mulch to dehydrators and anaerobic digestate, to more clearly describe their products, as well.

The AAPFCO registers and regulates the distribution of fertilizer, soil amendments and liming agents. The groups members are made up of members of state agriculture departments. Some states automatically use AAPFCO’s definition in their definitions of compost; others can choose to amend their regulations with the updated definition, Alexander said.

The new definition is especially important because the compost manufacturing industry has worked hard to determine, train and educate producers about management practices such as process that use mesophilic and thermophilic temperature stages to reduce pathogens.