I’m confused about the terms organic soil amendments and natural soil amendments. Where can I find more about each, and most importantly, lists of approved substances for each?

Answer: There are two places where you can find information about allowed (and specifically prohibited) organic soil amendments: OMRI (Organic Materials Review Institute) and the USDA National Organic Program (NOP).OMRI’s searchable database can be accessed at http://www.omri.org/ubersearch. If you search this database with “soil amendments,” a long list will be generated that has links to more detailed information.OMRI maintains general lists of generic allowed substances (“lime,” for example), as well as lists of product trade names of allowed soil amendments. A very general rule of thumb (which has many exceptions) is that natural products are generally considered acceptable, and synthesized products are prohibited.NOP’s listing of allowed and prohibited substances can be accessed at http://www.ams.usda.gov/rules-regulations/organic/national-list.You can also check out the ATTRA publication, Organic Materials Compliance, which may provide some clarification to your confusion about what is allowable in organic production versus what is “natural” (which is a very generic term).