Sphagnum peat is the preferred medium for casing in commercial application. Hobbyist & enthusiasts use a mix consisting of 50:50 peat:vermiculite with gypsum and lime for added calcium & to buffer pH to around 7.5.
Sourced from a specialized mushroom substrate supplier, made of select long-fibered blond sphagnum peat moss for general commercial use. It provides a high degree of water retention and air porosity for a wide range of applications that require high fibrosity and high moisture.