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== What is a Casing Layer? ==
A casing should be a non-nutritious top layer that is placed over a colonized substrate, if you use a nutritious casing it will be colonized by the mycelium and then it will no longer be a casing. The purpose of a casing is to create a microclimate above the substrate to help induce pinning, it also supply moisture to the substrate and the developing fruits and prevents the substrate from drying out too quickly. The high-humidity microclimate helps to minimize side pinning by making the conditions at the top of the cake more favorable for fruiting than the sides. Some casings also contain microorganisms that are both necessary for fruit-body formation in some species, and can also help fight off contaminations.

=== Benefits of a Casing Layer ===

* Provides a humid microclimate on the surface of the substrate in lower humidity environments.
* Prevents the substrate from drying out too quickly in lower humidity enviropnments.
* Supply moisture to the substrate and developing fruits.
* Helps prevent side pinning.
* Some species won’t fruit at all without the application of a casing.

=== Downfalls of a Casing Layer ===

* Casing layers do involve an extra step in the growing process, which means more time and resources to get the job done.
* They can also be susceptible to contamination, especially in fruiting environments with limited amounts of fresh air.

== When to use a Casing Layer ==
Since not all mushrooms really benefit from a casing layer, using one can sometimes be counterproductive. So use it if you have to, otherwise don't. Cubensis generally don't require a casing when fruiting in a Monotub or SGFC (with the exception of a few slow fruiting strains like Penis Envy) as the humidity is kept to near 100% due to the small size. When using a grow tent you should <u>always</u> use a casing as the humidity is lower, if you don't you will get side pins galore and the substrate will dry out quickly.