Casing

The casing layer is a layer of material that is applied on top of the colonized substrate to provide a favorable environment for fruiting. The casing layer serves as a protective layer, as well as a water reservoir, which helps to maintain humidity levels and promote the formation of fruiting bodies. Casing layers are commonly used in the cultivation of certain mushroom species, such as Agaricus bisporus (button mushrooms), and are an important part of the cultivation process for achieving optimal fruiting conditions. Some species will not fruit without a casing layer, while other species do not require a casing layer but fruit quality and yields are often improved with its inclusion.

Casing materials can include peat moss, vermiculite, coir, or a combination of these materials. The casing layer is usually applied after the substrate has been fully colonized by the mycelium, and the layer is typically between 0.5 to 2 inches thick. It is sometimes amended with nutrients to help improve yield and quality of the mushrooms.

Casing layers can also help to provide nutrients and support for the formation of the mushroom fruiting bodies. The mycelium colonizes the casing layer and forms a network of hyphae, which helps to support the development of the fruiting bodies.