I am trying more flowerpots around my landscapes to add color in areas without flowerbeds. I have tried several different potting soils that I purchased from wholesale/retail garden centers. I don't have much storage space, so can't order pallets of media from wholesale suppliers. I've noticed there is a big difference in content of the different media. How do I know what to buy? — via the Internet
You are right to be confused. There are no mandatory regulations concerning potting media, although there are voluntary standards that were developed by North Carolina State University and adopted by some producers. Products labeled as “potting soil” are not required to provide any additional information except volume or weight of the product, who manufactures it and where. These soils can be organic, inorganic or a combination. Many manufacturers have not conformed to the voluntary standards. The result is that there is a wide variety of products out there. So many that researchers at Utah State University evaluated 24 different brands, widely available at regional and national retail chain stores, for physical and chemical properties, in an effort to assist people in the industry. They found an amazing array of differences between the products. They measured water content, water retention and porosity, to name a few physical properties. They also measured pH, nitrate-N, phosphorus, potassium, calcium and magnesium content. Water retention ranged from 2 to 71 percent; porosity ranged from 34 to 92 percent by volume. Products containing wetting agents did not necessarily rewet better than those without. The pH ranged from 4.0 to 7.5, with only 12 of the 24 media in optimum range of 5.5 to 7.0. Surprisingly, some products that specified “fertilizer-added” had lower nutritional value than some that did not specify. Some package labels indicated the presence of components that were either underrepresented or not present at all.
The important thing is to consider how you grow plants and what type of medium you have success with. We all have different tendencies — some towards underwatering, others overwatering, some favoring several fertilizer applications during a season or one at the beginning and nothing later (not recommended). Your challenge is to do what greenhouse growers and container nurserymen have done: Find a medium you are successful with and stick with it. If you start to see inconsistencies in success, it is possible the producer has changed the recipe. Find a new one. Good luck and keep adding color.
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