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Plant Answer Line Question

Keywords: polymer-coated fertilizer, Fertilizers

Can you tell me what is in Osmocote? Every time I buy plants at nurseries and sales, the containers are full of these little round fertilizer pellets that get into my garden soil and never seem to decompose. Also, I try to grow organically, and I suspect this stuff is synthetic.


There are various formulations of Osmocote, marketed by the Scotts Company as "plant food." You can look up the Material Safety Data Sheet for each of them. I looked at the MSDS for Osmocote Plus, and nothing on the product label suggests that this is a certified organic product. It contains nitrogen, phosphate, soluble potash, and various minerals. The "sources" are coated in polymer. According to this article on "PCFs" (polymer-coated fertilizers) by Douglass Jacobs, published in the 2005 USDA Forest Service Proceedings, the type of polymer material in fertilizers (such as Osmocote) varies and the degree to which the fertilizer is released will vary accordingly. Here is an excerpt:
"The coating technology in Osmocote (OM Scotts Company, Marysville, OH) was developed in the 1960s, and this coating is classified as a polymeric resin. The coating process involves coating a soluble fertilizer core with a thermoset copolymer of dicyclopentadiene and a glycerol ester (linseed oil) dissolved in an aliphatic hydrocarbon solvent."

I am not a chemist but if I feel I ought to be in order to understand what the polymer coating consists of, chances are good that it is not something one would want in an organic garden. Although it is written by a local gardener and not a scientist, you may find this article about polymers from Paghat's Garden of interest. For a scientific approach, see horticulture professor Linda Chalker-Scott's article on polymers (albeit in hydrogels, not fertilizers). Seed coatings made with synthetic polymers are prohibited for certified organic use, according to the Organic Materials Review Institute: "Prohibited when the treatments are synthetic and not on the National List. Includes all synthetic pesticides and any synthetic materials not explicitly listed, plastic polymer pelletization, and genetically modified sources of seed." However, I was not able to find out anything about the composition of the polymer material. Seed treatment products which are "allowed" by OMRI are non-synthetic.

If you can bare-root most of your plant purchases and dispose of the polymer pellets in the trash, you may be able to avoid introducing them into your landscape. I also suggest talking to your favorite nurseries and asking them to seek more environmentally friendly alternatives.

Date 2018-04-21
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May 31 2018 13:14:08