Video by GrowCycle 

What is a Mushroom Substrate?

How to use mushroom substrates properly to grow the best mushrooms on planet Earth.


What is a Mushroom Substrate?

A mushroom substrate is the base that you grow your mushrooms on. It both provides nutrition and a structural base for strength like soil does for plants.

A mushroom substrate or spawn comprises three main components:

1) A base material which provides nutrients that will support mycelial growth; (The Mushroom Substrate Itself.)

2) Mycelium, which grows from spores in the substrate;

3) Water content, which allows water to move through the substrate, so it does not dry out too quickly.

The type of substrate chosen depends upon what kind of mushroom you want to grow.

Which Substrates Are Best For Which Types of Mushrooms?

Wood chips – Wood chips are one of the oldest forms of substrate. They provide a great base for many varieties of mushrooms, including shiitake, maitakes, portabellos and reishi.

Straw – Straw has been around since ancient times and is still commonly used today. It works very well for white button mushrooms because its high water content makes it easy for the mycelium of those mushrooms to spread out. The cheap but sometimes messy substrate for Oyster Mushrooms. Not as powerful for nutrients as the “Fast Fruiting Mix” but popular with some growers. Straw Pellets make using straw easier.

Sawdust – Sawdust is another old standby. Not just any sawdust, but sawdust from oak, and hardwoods seem to get the best results with many mushroom varieties, or species. Sawdust is a key component in the most popular substrate, mixed for Oysters and several other gourmet varieties. Oak pellets are compressed and formed sawdust from processed oak. These are ideal for use in mushroom substrate.

Many supplements are used, like Soy Hulls, and brans to boost the nutrition available to the Mycelium and later the fruiting body development of the mushrooms in your grow room.

Coco Coir – Made from ground coconut shells and husks, this substrate is often paired with Vermiculite in a 50/50 mix for an ideal mix for certain varieties. A few growers who have better access to Coco Coir use this instead of hardwood sawdust or hardwood pellets like oak. More based on the availability of it, instead of optimal growing mediums.

For a standard mix with dried coco coir (about 1.5 lbs), add eight cups of dry vermiculite, along with 16 cups of boiling water. Oyster mushrooms seem to like Coco Coir almost as much as the “Fast Fruiting Mix“, or “Masters Mix”. It allows good airflow and water retention when you use vermiculite.

Soy Hulls – Soy Hulls are a preferred substrate ingredient that is added to a 50-50 mix with oak sawdust to create an ideal combination, often referred to as the “Masters Mix”. Many gourmet mushrooms love this substrate. Every type of Oyster Mushroom responds very well to this “Fast Fruiting Mix”

When mixing your “Fast Fruiting Mix” using Fast Fruiting Pellets, all you have to do is weight the pellets out. Measure 5 cups or 2 lbs of pellets then add 3lbs of water and mix. Your result will be a 5lb set of substrates that are ready to bag, bucket, and sterilize. Then you can inoculate after your sterilized substrate has cooled.


Pasteurizing or Sterilizing the Substrate

Substrates used to grow mushrooms should be sterilized to prevent any contamination from growing instead of your desired mushrooms. When you are creating a great substrate, you are in effect proving the optimal environment for mold and other contaminants to grow. The sterilization process and the clean room processes you use during inoculation will give your mushrooms the growing advantage and help you secure the best growth possible.


This may include:

1) Pasteurization–heating the substrate to around 150–185 deg F for several hours until no bacteria remain.

2) Sterilization–heat treating the substrate to over  250 deg F for more than an hour.

3) Heat treatment + pasteurization–combining both methods above.


There are many ways to go about the task. Commercial growers like to use pressure canners or cookers like the “All American” for this task. These are very well-made and hold up with regular commercial use. Starting farms might use a less costly pressure cooker, but caution must be used with any pressurized vessel, since sterilization is rarely the intended use of cheaper pressure cookers, or canners.

How To Sterilize Mushroom Substrate Without A Pressure Cooker

When starting mushroom growing on a budget, some choose to cook their substrate in the oven at over 250 for several hours. This is costly on electricity but only requires a large foil pan like those used for your Thanksgiving Turkey, and some aluminum foil. It is not efficient, but can be a place to start when you are on a budget.

Others choose to use steam in a steam barrel that they build, or buy for the purpose. This is less costly than some other options and can allow you to treat large amounts of substrate with heat and modest steam pressure.


What Makes a Good Mushroom Substrate?

The first thing to consider when choosing a good mushroom substrate is whether it has enough water content. Water content refers to the amount of liquid present within the substrate. A high-water content means there’s plenty of water available for the mushrooms to absorb. This makes them happy because they don’t have to work as hard at absorbing nutrition from the air.

Another factor to take into consideration is pH level.

Substrates should also have 1-2% nitrogen for the best fruiting body results. Therefore many types of substrates that are used are supplemented.

Just like soil, the better quality of the substrate the better the outcome with your yield, taste, and even look of your mushrooms. While it may be possible to grow mushrooms in almost anything you sterilize, if you are growing for a profit, having the highest quality gourmet mushrooms should be your primary concern. Give your mushrooms the best help in the growth cycle. A small investment in quality substrate ingredients will mean more happy paying customers for your gourmet mushrooms.