A substrate is a bulk material that the mushroom mycelium can use for energy and nutrition and mainly as a stored water source. A good substrate is required in order for the mushroom to grow and to fruit.

Common substrate recipes for growing mushrooms usually involve coco coir, manure, straw or hardwood sawdust, although there are many other good options to be considered.

The mushroom substrate needs to be properly prepared by adding water, potentially adding additional nutrition, and further processed by sterilisation or pasteurisation. When ready, it can be “Inoculated”, wherein broken up pieces of mycelium-covered grain, also known as grain spawn, are evenly mixed into the substrate.

Under the right conditions, the mycelium will start to grow, rapidly devouring and decomposing the organic material in a process known as “colonisation.”

The mushrooms are ready to fruit once the substrate is fully colonised- meaning it has been completely consolidated and encompassed by the mycelium.


Ideal mushroom substrates are moist and full of nutrition. Unfortunately, there are many other things that also thrive in these conditions, such as molds and bacteria. These contaminants can grow much faster than the mushroom mycelium, so something needs to be done in order to give the mushroom an advantage in the race to colonize the substrate.

This can be accomplished by the process of sterilisation or pasteurisation.

Pasteurisation is the process of heating up a substrate between 65c-75c for a period of 1.5-2 hours. It doesn’t remove all the contaminants, but it will reduce the overall population of other microbes to a level that gives the mushroom species a head start.

Some microorganisms will survive pasteurisation and remain in the substrate in some capacity, but can actually helpful for the growth of the mushroom in the long run.


The process of heating a bulk substrate between 150 – 185 deg F with steam or in a hot water bath in order to reduce the overall level of contaminates and give the mushroom culture a head start.


The process of heating the substrate to extreme temperatures exceeding 121c, under pressure, in an attempt to completely eliminate any living or dormant contaminants within the substrate.


Mushroom fruiting bodies are 70-90% water, and all of that water is drawn up from the substrate. Unlike plants, mushrooms are not “watered” during the growing cycle.

Of course, humidity needs to be added to the air so that the substrate doesn’t dry out, but all of the water that mushrooms require to grow is added to the substrate before inoculation.

For this reason, the substrate needs to be properly hydrated during preparation. If your substrate is too dry, growth will be slow, and the mushrooms may fail to overtake the substrate at all. On the other hand, if the

substrate is too wet, it may encourage bacterial growth and inhibit full colonisation. Getting just the right amount of water in your substrates definitely takes some practice.

In the remainder of this video we will go over how to make a bulk substrate used in monotubs, we will go over how to make other substrates in a future tutorial.

Bulk substrates for monotubs are made from a combination of the following : manure, coco coir, vermiculite, and gypsum.

Most modern growers are leaving out the manure and making their substrate from just Coco coir, Vermiculite and Gypsum, also know as CVG.

This bulk substrate is low in nutrition and can be easily pasteurised, some people don’t even properly pasteurise and get away with adding hot water and letting it steam in a bucket, we prefer to pasteurise properly but if you are interested in a quicker method google “CVG Bucket Tek”.

The ratios for this recipe are not that important but we use 500g coco + 3l vermiculite + 15g gypsum. It is difficult to advise on exactly how much water to add as this may change with different types of coco coir but we use around 3l of water. Water needs to be add until it reaches “Field Capacity”. Slowly add water until when you grab a handful of substrate and squeezer it hard only a few drops come out. Check out this video on field capacity.

Once at field capacity we put the substrate into a heavy duty bag, get a large pot of hot water ready on the stove ( at about 80c) add the bag of substrate and keep testing the heat. When the temperature in the centre of the substrate gets to 70c start timing and leave it for 90 minutes. Your substrate is ready to use once it has cooled back to room temperature.