Mulch can be broken into three basic types based on its quality and usage. These types are Biological, Commercial, and Industrial.
Biological - This is the highest quality mulch and therefore the most beneficial in improving soils, preventing disease, protecting plants, etc. It has a low carbon-to-nitrogen ratio so it does not steal nitrogen from the soil and weaken or stress plants. It has been composted to kill weed seeds and pathogens. Composted "native mulch" and "coarse screened compost" are examples of this class of mulch. The bag will have holes in it so that air can enter allowing the beneficial microbes to breath and be kept alive. This mulch will typically sell retail for $5-7 per bag (2 cubic feet).
Commercial - This is a middle grade of mulch made from tree barks (pine, hardwood, etc.) and is the most common. It will be in a sealed bag and may have a sour, stale or strong odor. It has a high carbon-to-nitrogen ratio and robs soil of nitrogen and other nutrients. Tends to float off in a heavy rain or develop unsightly molds and fungal mats and may attract fire ants or termites. This mulch will typically sell retail for $3-4 per bag (2 cubic feet).
Industrial - This is the lowest grade of products called mulch. It is made from industrial wastes like old pallets, construction wood, etc. It is often chemically burned black with industrial waste and will sometimes rub off in your hand, and it is often dyed various colors. It often contains arsenic from CCA treated waste wood. It has a very high carbon-to-nitrogen ratio and robs nitrogen and other nutrients from the soil for a long time. It may be extremely alkaline and high in toxic salts. This product will typically sell retail for $2-3 per bag (2 cubic feet).
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