Although rock wool is lightweight, it is bulky during transportation and storage, unlike coco slabs which can be highly compressed and then expanded with water before use. Rock wool needs to be placed on a completely flat surface to make the water gradient inside the product uniform and to prevent any saturated or overly dry patches.
Although it can be used for more than one crop, and some recycling programs have been developed for used rock wool, disposal remains a problem for many growers because rock wool does not decompose or degrade over time. The fibers of rock wool board can irritate the skin, and if handling granular rock wool or handling old rock wool products, the use of a mask is recommended.
New or inexperienced growers need to determine the correct irrigation frequency and amount for rock wool systems, as this may differ from other substrates such as perlite and coco.
Rock wool does not contain naturally occurring nutrients (coco usually contains a certain level of potassium, and sometimes other minerals used for pre-treating the substrate), so plants are completely dependent on a balanced and complete hydroponic nutrient solution at each growth stage.
Rock wool is an inert substrate made from rock and does not contain naturally occurring growth stimulants, such as humic acids, other organic compounds or naturally occurring beneficial microorganisms, although these substances can be added using quality hydroponic supplement products.
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