Few mushrooms, if any, will appear on the surface of the compost in the absence of some type of covering of the colonized compost. In mushroom growing, the process of covering the compost at this time
is called “casing”. The materials used to “case”, consists of a blend of peat moss and limestone that is saturated with water . The mycelium begins a journey through the casing material  to the surface of the compost. Continued hand waterings are applied  in an attempt to maintain saturation levels in the casing material. The casing layer provides a water reservoir and an environment in which the mycelium changes from the vegetative stage to the
generative or fruiting stage. Depending upon the growth characteristic of the strain used, the temperature and moisture of the casing layer, the first mushroom will mature to be harvested with 21 to 26 days from the day of casing.
 Casing material being put on top of trays that have just been inoculated with spawn