Grow mushrooms the EZ way.

How To Make A Casing Layer For Growing Mushrooms.

Cased Shoe Box Grow

How To Make A Casing Layer For Growing Mushrooms.

A casing layer is a soil-like material that is applied to the surface of a growing medium, such as sterilized sawdust or compost, in which mushroom mycelium (the vegetative part of the mushroom) is already growing. 

The purpose of the casing is to provide the necessary conditions for the development of the mushroom fruiting bodies (the part of the mushroom that is typically eaten).

Casing layers are not supposed to be nutritious to the forming fruiting bodies but rather provide a moist and aerated environment for them to develop in.

Casing is not always necessary however they have been shown to improve oyster mushrooms yields and can promote pinning in non ideal conditions.

Think of a casing layer as a super hydrated divider between the substrate and the outside world.

The mycelium reaches a casing layer which it cannot use as a source of food however it is aerated and moist, this initiates pinning.

For some mushroom strains, the application of a casing layer is essential for the formation of fruiting bodies.

Overall, casing is a crucial element of mushroom cultivation that is widely used by experienced mushroom growers and should probably be used more by beginner growers.

How To Make A Casing Layer.

Materials and Equipment.

Note: I am going to pasteurizing the casing layer using a Instant Pot as it requires less monitoring and has precious temperatures. However if you don't want to use one of these, use a cooking thermometer and a stove instead.

Alternatively you could use an instant pot if you have one.

The Casing Layer Recipe

Begin by mixing equal parts peat moss (50%) and vermiculite (50%) by volume in a mixing bowl.

To do this I will use 2 cups of peat moss and 2 cups of vermiculite.

Adding verm to peat moss

Mix the vermiculite into the peat moss using your hands.

Pre hydrated Casing Layer

Next place your casing layer inside a brewers bag.

Casing into brewing bag

Pasteurize the casing layer at around 60c-80c (140f-176f) for 2 hours in a water bath, I will be using my Instant Pot for this. 

Normally I like to put mine on around 75c, this is where I have noticed the most consistent temperatures in the casing soil.

pasteurizing casing in instant pot
Sous vide pasteurization mushrooms

Remove the casing layer from water.

Allow the casing layer to strain and cool down in the pot for an hour or 2.
I like to hang mine up to drain as shown below.

Draining casing

When complete it should look like this below. I squeeze out excess water leaving it at field capacity (only a few drops of water fall when squeezed).

Mixed saturated casing soil

Spread the casing mixture evenly over the surface of the bed. It should be aerated and not compact. 

To do this I like to get a handful, squeeze it to ensure it is field capacity (one of two drips of water come out), then crumble it using my hands onto the surface.

Cased Shoe Box Grow

Once the casing layer is applied, place the container or tray (with its lid on) in a suitable location for fruiting.

Maintain the casing layer by keeping it evenly moist and misting it lightly as needed. 

I check if it needs misting by just lightly tapping the surface to with the back of my hand (after its been cleaned with soap) to check if it is still moist.

Pins growing in casing layer

That's it!

With these steps, you can create a casing layer using peat moss and vermiculite that will help to support the growth and development of your mushrooms. 

Pins In Casing Layer

What Does A Casing Layer Do?

A casing layer can help to maintain this high level of humidity at the surface of the substrate, even if the air in the fruiting environment is less humid. 

Primordia, the early stages of mushroom development, typically form in environments with a humidity of 99%. 

Once the mycelium on the substrate reaches a casing layer it will initiate pinning as the environment is perfect and there is nothing else to consume.

This allows for more flexibility in the cultivation process when environmental conditions are not optimal.

Casing layers perform the follow roles in mushroom cultivation: 

First, it helps to maintain moisture levels in the growing medium, which is essential for the pinning, growth and development of mushroom fruiting bodies.

This is because mushrooms require a high level of humidity to form pins. 

Casing also helps to regulate temperature and air exchange, which are important factors for mushroom growth.

In addition, casing helps to promote the formation of the mushroom fruiting bodies by providing a surface for the mushroom mycelium to grow on and by stimulating the production of the hormones that signal the mycelium to begin fruiting. 

Casing also helps to protect the growing medium from contaminants, such as bacteria and fungi, which can interfere with the growth of the mushroom.

How Thick Should A Casing Layer Be?

The thickness of the casing layer in mushroom cultivation can vary, but it is generally recommended to be around 1-2 inches (2.5-5 cm). A good rule of thumb is to have a casing layer that is 1/2 inch thick for every inch of substrate.

A thicker casing layer can provide more moisture and insulation, but it can also take longer to colonize and can lead to an over-supply of moisture, which can encourage the growth of unwanted bacteria or mold.

Does Casing Increase Yeild?

Yes. Research has shown that the use of a casing layer can result in larger and more consistent crops, as well as a faster and more reliable fruiting cycle.

Research in PubMed titled “Effect of casing layer on growth promotion of edible mushrooms” showed how casing with pasteurized casing soil increased yields of mushrooms.

It discusses how beneficial bacteria left in the casing soil after pasteurization may be one of the reasons for this, as sterilize casing soil did not perform as well. 

Can You Use Coco Coir A Casing Layer?

Coco Coir alone is not a very good casing layer due to the fact that it contains nutrients which the mycelium will consume.

Coco Coir is sometimes added into a casing layer but never more than a 10% volume.

The purpose of a casing layer is to provide a non nutritious, aerated, moist barrier for the mycelium to begin forming fruits. 

Because coco coir is nutritious the mycelium will continue its colonization cycle when it reaches the coco coir instead of realising it is at the end of its nutrients and pinning.

Vermiculite as a casing layer?

Vermiculite alone is not a very good casing layer, however people have been known to use it in desperation. 

What Should The pH Of Casing Soil For Mushroom Be?

The ideal pH for a casing layer in mushroom cultivation is typically in the range of 6.2-7.2.

This pH range provides the right balance of nutrients and helps to reduce the risk of contamination by harmful bacteria or mold.

It is important to note that different species of mushrooms may have different pH requirements, so do some research before creating your casing layer recipe.

When Should You Add A Casing Layer?

A casing layer is typically added after the substrate has been fully colonized by the mycelium. 

In general, the casing layer is added once the mycelium has covered at least 95-100% of the substrate and hyphal knots have begun to form.

This helps to ensure that the mycelium has sufficient energy to support the growth of the mushrooms and that the casing layer will provide the necessary moisture, nutrients, and environment for optimal fruiting.


Thanks! Hopefully you have gained some knowledge on casing layers, honestly they are really helpful for people who struggle to get there mushrooms pinning (beginners) and i'm not sure why more people don't use them (probably because it adds an extra step to an already difficult/exciting process).

Further Reading.

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