Casing layer

The casing layer is a layer of moist material that is put on top of the substrate with mycelium, before exposing this substrate to the fruiting conditions. The usage of a casing layer is highly recommended.

The riceflourcake method, is the only method where a casing layer is not been used. In other methods other ingredients will be used as substrates and these substrates will in a later moment be covered with a casing layer. This means that the substrate with mycelium itself will not be exposed directly to the outside air, which is the case with the riceflourcake method.

The casing layer makes sure the substrate doesn’t dry out; it stimulates the formation of mushrooms and also serves as a water container for mature mushrooms.

There are many different recipes for casing layers. During time and experience a lot of different casing layers have proved to be very effective.

Some recipes are:

  • 4 parts coarse peat
  • 1 part limestone flour
  • ½ part limestone grit
  • 2 parts water
  • 2 parts coarse peat
  • 1 part chalk
  • 1 part water

(both from Paul Stamets, The Mushroom cultivator, page 132)

We have had also very good results with the following casings:

  • 3 parts vermiculite
  • 1 part cactussoil
  • 1 part water


  • 3 parts vermiculite
  • 1 part water

Mix the dry components well together. Then steadily add the water and mix it well again.

Casing mix

Casing water

It is very important the casing layer will have the right degree of humidity. You have to go about this a little by instinct. A good way to check is to put a small amount of casing layer in your hand and squeeze. When the humidity will be right, a few drops of water will ooze through your fingers. If your entire hand gets wet, you should add some extra dry components. When there aren’t any drops, you should add some water.

Test casing

Now the casing needs to be sterilized. Put the casing in a jar and sterilize it for about 50-60 minutes in the pressure-cooker at 15 psi. Then leave it to cool off until it has cooled down to room temperature. Casing material can also be pasteurized, 60-70 °C, for 1 hour. Some cultivators even choose to not sterilize it or pasteurize it at all.

Casing steriliseren

When the casing in the jar has completely cooled off, your casing layer is ready to be used.

Casing klaar