Organic mulches consist of material that is 100% all-natural that has the ability to decompose on its own. Organic mulch is made up of material such as tree bark, grass clippings, straw, compost, and grape pomace. Organic mulch benefits the soil beneath it, protecting it and, allowing worms to gracefully move underneath moistening the soil keeping it fresh and alive. Earthworms add natural nutrients that you may have not known you needed in your soil. These nutrients consist of such things as potassium, phosphorus, nitrogen, and trace elements. 

Mulches that include plastic sheeting, rocks, rubber chips, or railroad ties are considered to be inorganic and will grow fungus over time. This material doesn’t have the ability to decompose on its own and has to be replaced more often. Most worms stay clear of this type of mulch, making it harder to maintain moisture and the natural nutrients throughout the mulch. Inorganic mulch has the tendency to increase temperate and can be harmful to the plants in that area. 

https://www.thedirtbag.com/topsoil-vs-garden-soil-whats-the-difference/

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