Casing is a fruiting method where a colonized substrate is covered with non-nutritious layer such as peat moss, vermiculite or different mixtures of the previous with various additives. The purpose of this inert covering is to help induce fruiting and to supply moisture to the substrate and the developing fruits.
Vermiculite is used in nearly all casing recipes because of it's completely inert nature (nothing can grow on it) and because it can hold 16 times its weight in water. It is inexpensive and can be found at many garden and hydroponics shops.
Peat moss is unconsolidated soil material consisting largely of undecomposed, or only slightly decomposed, organic matter accumulated under conditions of excessive moisture. It is a main ingredient of many casing formulations, its pH ranges from 3-4 (acidic), has to be brought to neutral or slightly basic (pH 7-8) by adding a buffer (limestone flour, calcium carbonate or oyster shells)
Coconut coir is the crushed outer shell of the coconut fruit. It is excellent at retaining water and can hold nearly as much as vermiculite. Unlike other casing materials, coconut coir is nutritious and is often used as a bulk substrate. For this reason, many cultivators experience overlay (mycelium growth over the casing) when using a coir based casing layer.
Several mineral supplements are beneficial to casing material since they can provide essential minerals for mushroom growth and can be used to balance the pH of the casing. By raising the pH of the casing layer, the casing layer is made inhospitable to fungal contaminants, which are less tolerant of a high pH than established mushroom mycelium.
- Gypsum (calcium sulfate dihydrate) provides calcium and sulfur and acts as a buffer
- Hydrated lime (calcium hydroxide) provides calcium and raises the casing pH (reduces soil acidity)
- Limestone flour (calcium carbonate) provides calcium and raises the casing pH (reduces soil acidity)
- Crushed oyster shells consist of primarily calcium carbonate and provide similar benefits to hydrated limestone flour.
Casing material is most commonly prepared by combining the water reserving materials and supplemental minerals while dry (in order to ensure that no minerals clump together) before adding water to field capacity. After the casing mixture is made, the mixture can be either pasteurized or sterilized. Many cultivators suggest that pasteurization is more appropriate because it allows some beneficial organisms to remain in the casing material.