Compost Feedstock Requirements

What are the rules around feedstocks for compost that is compliant under the Canadian Organic Standards?

By Ana Negrete

Organic growers can implement various practices on their farms to help establish and maintain a fertile soil as indicated in the Canadian Organic Standards. A common practice is composting. Whether growers make their own compost or use compost from an off-farm source, the requirements for the compost feedstock are the same.

Acceptable compost feedstock materials are described in Table 4.2 of CAN/CGSB-32.311, the Permitted Substances List (PSL), and include manure, animal and plant materials, soils, minerals, and paper yard waste bags that may contain colored ink. However, these materials may need to comply with additional criteria in order to be allowed. This article explains some of the criteria for commonly used compost feedstock materials.

Manure must comply with subclause 5.5.1 of CAN/CGSB-32.310, General Principles and Management Standards. This means that organic manure should be used when commercially available, and if manure from non-organic sources is used it must meet specific restrictions. The manure must come from livestock not kept in a fully caged system where animals are unable to move 360 degrees, and have not been kept permanently in the dark. The source and quantity of manure, the type of livestock, and evaluation of these livestock living conditions must be recorded.

The use of food and yard waste that has either been contaminated with prohibited substances or that contains genetically engineered (GE) plant material is strongly discouraged, but it is not prohibited unless the prohibited substance persists through the composting process. If biodegradable bags are used to collect the food or yard waste, they must decompose effectively during the composting process. Confirmation that petrochemical residues do not persist after composting may be required.

Minerals should not have undergone any change to molecular structure through heating or combining with other substances, and should not be processed or fortified with synthetic chemicals unless listed in Table 4.2 of the PSL.  

Soil must come from an organic farm where prohibited substances have not been used for at least 36 months.

As with food and yard waste, compost feedstocks that may contain prohibited substances listed in clause 1.4 or 1.5 of CAN/CGSB-32.310 that are known to be persistent in compost are not allowed. Compost manufacturers can prove that their compost does not contain persistent substances by providing test results for the compost, or by providing documentation showing that the potential contaminants in their feedstock(s) will degrade during the composting process. 

This article was originally published in the summer 2018 edition of the OMRI Materials Review newsletter, and was revised in June 2022 by Senior Bilingual Technical Coordinator Tina Jensen Augustine.