OMRI Strengthens Microbial Fertilizer Review Requirements to Address High-Risk Media

August 3, 2026

OMRI is strengthening its review requirements for microbial fertilizers in response to increasing concerns about microbial fertilizers derived from synthetic media sources. Synthetic fertilizers are prohibited by the NOP regulations at §205.203(e)(1), with an exception only for National List materials. And while microorganisms are inherently non-synthetic, microbial fertilizers that contain residual media/spent broth or chemicals produced through microbial processes are at risk of contributing plant nutrients from synthetic sources, which is prohibited by the NOP standards.  

Microbial fertilizers include microorganisms and fermentation products that serve as crop fertilizers (i.e., products that supply nutrients to plants for growth and development). These products are listed in the Crop Fertilizers and Soil Amendments (CF) Class, and may contain a mixture of microbial exudates, growth media, and microorganisms, or these components may be individually isolated during the manufacturing process. The new policy changes how substrates/growth media (hereafter referred to as “media”) are reviewed for such products, specifically when the media may be at high risk for contributing plant nutrients to the final product (i.e., nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, boron, chlorine, cobalt, copper, iron, manganese, molybdenum, nickel, selenium and zinc).

To understand the new policy for the review of media sources of microbial fertilizers, we must discuss OMRI’s policy for growth media removal. OMRI’s general policy regarding media removal for microbial products is that the media does not require review if we understand it has been removed from the final product by physical means (e.g., filtration, centrifugation, etc.) or it has been consumed by the microorganisms. This applies regardless of the identity of the media components and their synthetic/nonsynthetic status. 

Under the new policy, growth media that is removed by physical methods remains exempt from review and residual media (i.e., microbial growth media that is neither consumed nor physically separated from the microorganism or fermentation product) remains subject to review for all types of microbial products, including microbial fertilizers. That is not changing. 

What is changing is that high-risk media (media which may be contributing plant nutrients to the final product) now requires additional review. The following conditions now apply to products identified as microbial fertilizers:

• For microorganisms and fermentation products that are not physically removed from the spent broth/media, all media at high risk for contributing a plant nutrient to the final product requires review to verify their synthetic/non-synthetic status. 
• Microorganisms that are physically removed from the spent broth/media are exempt from media review. The growth media assimilated into the biomass of microorganisms is not subject to review. 
• For fermentation products that are physically removed from the spent broth/media (e.g., isolated amino acids), review of the high-risk media is limited to those components that contributed to the chemical composition of the fermentation product.
• High-risk media that is subject to review must be nonsynthetic or synthetic and allowed at 205.601(j) of the National List of Allowed and Prohibited Substances. The use of synthetic materials appearing at 205.601(j) must be in accordance with any annotations on the National List and may result in a restricted OMRI listing for a product.

OMRI will be conducting Limited Re-Reviews of listed products impacted by these changes and issuing new certificates as appropriate. This specifically applies to products in the CF class identified as containing microbial fertilizers. Affected suppliers will be notified within 60 days from when a Limited Re-Review is initiated. More information about the Limited Re-Review process is provided in §2.10.1 of the OMRI Policy Manual©. 

Contact Information:

Nick Stansbury
Review Program Technical Manager
(541) 343-7600, ext. 134