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Sources of Organic Fertilizers and Amendments

Agronomy Resource List

by Andy Pressman
NCAT Agriculture Specialist
February 2014

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How to Use This Resource List: For your convenience, you can now search for suppliers by state, by product category, or by using a keyword. Before beginning your search, however, you are encouraged to read About This List and What Can I Use in Organic Crop Production.

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About this List

Organic farming is a whole-system approach to optimizing the natural fertility resources of a farm. It works through traditional practices of recycling farm-produced livestock manures, composting, crop rotation, green manuring, and crop residue management. Secondarily, organic agriculture looks to local waste products—manures, food and seafood processing wastes, etc.—to supplement soil fertility economically.

While many organic operations achieve a high degree of sustainability using these methods, innate nutritional deficits in regional soils, past management abuses, and high productivity demands often require the farmer to purchase additional fertilizers or amendments from specialty suppliers.

This resource list is a guide to suppliers of bulk organic fertilizers and specialty soil and foliar amendments, and is geared to commercial farmers and market gardener—especially organic producers. Sources are categorized by product type, and thus it also serves as an educational overview of the different organic fertilizers, biostimulants, inoculants, rock minerals, and other amendments available. The products and suppliers listed are based on the compilers' current knowledge of the materials available in the marketplace and the specific product offerings of each company listed.

Please note that this list focuses on manufacturers, regional and national distributors, and mail-order sources. It is not comprehensive and includes few localized dealers, as these would be too numerous to mention. Therefore, be advised that many of these materials and products can be found locally at farmers' co-ops, retail garden centers, nurseries, neighborhood organic supply outlets, and the like. This is especially true of plant and animal by-products, dried livestock manures, composts, fish emulsion, and seaweed extracts. Take the time to shop carefully Comparing prices and labels can yield significant savings.

It is important for the reader to know that mention of a product does not ensure its acceptability for certified organic production. (See the text box What Can I Use in Organic Crop Production?) Furthermore, many of the companies listed sell a wide range of products including some that are prohibited under the National Organic Standard. It is the responsibility of the grower to consult with his/her certifier and determine the acceptability of any questionable material or product.

Finally, the mention of a company or individual in this list does not constitute an endorsement of that company, its products, or its business practices, by NCAT, the ATTRA Project, or the USDA.

Qualified businesses not presently included in this list should contact Andy Pressman at ATTRA for inclusion in future updates. Updated information should also be addressed to his attention. Contact Andy at:

Phone: 800-346-9140, Fax: 479-442-9842, or E-mail

What Can I Use in Organic Crop Production?

(adapted from NCAT's Organic Crops Workbook, Section VI)

One of the greater difficulties that organic producers face on a regular basis is determining whether or not a particular product or material can be used in organic production. Sad to say, the problems are real, but some basic clarifications will help. First of all, all natural or nonsynthetic materials can be assumed to be acceptable in organic production. There are a few exceptions, however, which will be explained shortly.

Most organic producers and prospective producers have heard about the National List. §§205.600-205.619 of the National Organic Program Regulations comprise the National List; §205.601 and §205.602 are those directly pertinent to crop production. (See the National Organic Standard on the NOP Web site.) §205.601 includes synthetic materials that are allowed in organic crop production, for example, sulfur, insecticidal soap, etc.; §205.602 contains natural, or nonsynthetic, materials that are prohibited, for example, ash from manure burning, nicotine sulfate, etc. When considering commercial products, the grower must be aware of all ingredients to determine that none are prohibited. If a full disclosure of ingredients is not found on the label, details should be obtained from the distributor or manufacturer and kept in the grower's files. Note that such details must extend to inert ingredients. When in doubt about the acceptability of any material or product for certified organic production, contact your certifier.

An important organization to know about is the Organic Materials Review Institute (OMRI). OMRI is a non-profit organization that evaluates products for suitability in organic production and processing. OMRI does not have status as a regulatory body. However, its decisions with regard to the acceptability of commercial products is highly respected and accepted by most certifiers. OMRI Listed products can be purchased and used with a high degree of confidence. Producers should be aware, however, that there are many acceptable products in the marketplace that have not been evaluated by OMRI and do not carry the OMRI Listed seal. Again, it is important to contact your certifier to verify whether a particular product or material can be used. To contact OMRI and see their Brand Name Materials List, visit their Web site or contact OMRI, Box 11558, Eugene, OR 97440; 541-343-7600.

For more information...

For additional information about organic agriculture and its principles, please ask for ATTRA's Overview of Organic Crop Production. For details on how to become a certified producer, ask for the ATTRA publication Organic Farm Certification and the National Organic Program. For guidance on how to comply with the National Organic Standard for crop production, request NCAT's Organic Crops Workbook. For further information on how organic fertilizers can be integrated into organic farming systems, ask for ATTRA’s Alternative Soil Amendments and Manures for Organic Crop Production publications.

Qualified organizations not presently included should either use Submit/Update Listings or contact Andy Pressman at ATTRA for inclusion in future updates. Updated information can also be addressed to their attention.

E-mail Andy Pressman or call:


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This page was last updated on: November 6, 2018