All About Mushroom Substrates (2024)

The mushroom substrate you choose may just be one of the most important decisions of your life…

Just kidding, but it’s pretty important if you are concerned about your yields.

New growers tend to think that growing mushrooms is like growing plants. Sure, they both come from the dirt, but that’s about where it ends. While plants do rely on nutrients from the soil, they rely on photosynthesis as their primary source of energy.

Mushrooms on the other hand do not require sunlight. They derive nearly all of their energy and nutrients from their substrate material. Therefore, it is paramount that you understand the substrate you use will directly affect your success.

What is Mushroom Substrate

Substrate, or “Sub”, is a bulk cultivation material that mushroom mycelium uses for nutrition, moisture, and energy. This can be a spawn material, i.e. high nutrient substrate used for colonization, or a bulk substrate used to mix with spawn substrate (colonized grains) to increase your yields.

There are virtually endless options of organic materials which can be used as mushroom substrates. But let’s not fuss around; instead, let us focus on the most common substrates.

The Most Common Mushroom Substrates

Manure – Commonly used for Button Mushrooms or other dung-loving species. Is frequently mixed with other non-nutritional substrate materials.
Coco Coir and Vermiculite – Excellent substrate for many types of mushrooms.
Soy Hulls – Used to grow a variety of medicinal and gourmet mushrooms. Most commonly mixed with other substrate materials.
Hardwood Pellets or Sawdust – Many hardwoods make an exceptional substrate for many varieties of mushrooms. Use hardwoods combined with bran or soy hulls for exceptional results.
Straw – Commonly used to grow oyster mushrooms.
Coffee Grounds – Mushrooms will grow on coffee grounds and many other waste materials.

Before deciding on a substrate it is important that you understand the needs and preferences of the mushroom species you are growing. From there you can research the best ingredients and additives for your substrate.

Regardless of the substrate material you choose, it will need to be prepared before use. Preparing substrate is the process of hydrating, additives, and pasteurization.

Substrate Preparation

Effective mushroom substrates are moistened and free of aggressive microbes that may compete with growing mycelium. With that said, there are two main elements to substrate preparation. These are Hydration and Pasteurization.

While there are other steps you can take to mitigate contamination, such as adding substrate additives, this article will focus on the basics.

Hydrating Substrate:

Mushroom fruit bodies may contain up to 90% water by weight. Unlike plants, mushrooms are not watered, and therefore it is important that the substrate is hydrated to a level that will provide the mycelium the ability to produce some fatty fruits. High humidity levels must also be maintained to prevent the substrate from drying out prematurely during the fruiting phase.

Pasteurizing or Sterilizing Substrate

Hydrated and nutritious organic material is a literal heaven on earth for not only your precious mycelium but also for more aggressive micro-organisms such as mold and bacteria.

Relatively speaking, mycelium is a very slow-growing organism compared to certain molds. In a head-to-head competition, mold will completely overtake the substrate before your mycelium has even moved in. That said, it is important that you take steps to eliminate any competing organisms so that your mycelium can fully colonize the substrate. Once the mycelium has moved in, mold will have a much harder time finding a place to squat.

There are two methods you can use to provide your mycelium a head start. These are pasteurization and sterilization.

Pasteurization: Substrate pasteurization is the process used to decimate the population of harmful/aggressive microbes while allowing good microbes to live. This is because certain microbes have a symbiotic relationship with mycelium and help to fight off competing organisms.There are two methods of pasteurization, Heat, and Cold.

Traditional “heat” pasteurization involves warming the substrate to internal temperatures of 140-180 deg F for a period of 1.5-4 hours.

Cold water pasteurization methods include the following:

Lime bath treatment
Peroxide treatment
Cold Fermentation

Sterilization: Substrate sterilization is the process of warming your substrate to temperatures exceeding 250 deg F. for a period of time. Under these temperatures all microbes will be killed, leaving nothing but a clean and sterile growing surface.

So when should you sterilize and when should you pasteurize?

The decision to sterilize or pasteurize will depend on a few factors. However, the general consensus is that any starter/spawn substrates, i.e. grain, seeds, should be completely sterile and bulk substrates are generally pasteurized.

Different Substrates for Different Mushroom Species

Although most mushrooms will adapt to whatever is available, each mushroom species has its own preferences. Let us categorize these as either wood-loving or dung-loving species.

Woodloving mushroom species will do very well on hardwoods, hardwood sawdust, and straw.
Dungloving mushroom species thrive on composted manure.

The most popular cultivated species that do well on hardwood sawdust or chips include Reishi, Lions Mane, Maitake, Shiitake, and King Oyster mushrooms.

The most popular cultivated species that do well on straw include Blue Oysters, Yellow Oysters, Pink Oysters, and Pearl Oyster mushrooms.

The most popular cultivated species that do well on manure-based substrates: Button mushrooms, Portobellos, P. Cubensis, and other psychoactive species.

Using Straw Substrate

Straw is a cheap and effective substrate material that you can pick up for a couple of dollars for a 40-pound bail. The downside of straw is that it is very messy to work with.

How to pasteurize straw with heat:

Cut the straw into lengths of 3-4 inches. A weed whacker in a garbage can will do the trick.
Pasteurize:
- Place a shredded straw in a mesh brewery bag, pillow case, or similar.
- Place a large pot filled 50-60% with water on the stovetop on high until the water reaches 180 deg F.
- Place the bag of straw in the pot of water allowing it to reach 160-170 deg F.
- Keep at this temperature for one hour.
Remove the straw from the pot and strain the straw until it produces no more than a few drops of water when squeezed.
Bag and innoculate the straw with colonized grain spawn.

Using Hardwood Chips or Sawdust Substrate

Hardwood sawdust is an excellent material for mushroom substrate, is cheap, and is often easy to find as it is a waste product.Sawdust is typically mixed with other materials such as straw, wood chips, bran, and other materials.

The most commonly used hardwoods include beech wood, hickory, oak, and maple. If you are unable to find hardwood sawdust in your area, you may buy hardwood pellets used for bbq smokers, but make sure you do not purchase anything that contains soft-woods or additives. A great option is the Camp Chef Pellets

Hardwood Lovers Substrate Recipe

If you are growing wood lovers using sawdust or pellets, the following recipe produces very good results. This recipe is for one 5-pound fruiting block.

5 cups of hardwood pellets
1.4 liters water
1-1/4 cups wheat bran (added as a supplement to increase yields)

The Master’s Mix

The Master’s Mix was discovered/developed by T.R. Davis from Earth Angle Mushrooms. This particular substrate mix is extremely effective when growing oyster mushrooms and produces massive yields on early flushes. This blend is hydrated to 60% and is sterilized.

Masters Mix Recipe:

For each 5-pound fruiting block you will need the following:

450 grams of soy hulls
450 grams hardwood fuel pellets
1.4 liters water
Mushroom grow bag
Pressure Canner/Cooker

Once bagged, sterilize the blocks at 15psi for 2-2.5 hrs.

Using Manure Based Mushroom Substrate

Mushrooms that prefer manure-based substrates include the Agaricus species, as well as many of the most common psychoactive species (magic mushrooms).

Manure substrates are easy to use, relatively easy to find, and easy to prepare. When making manure substrate it is common to mix composted manure with base (high moisture retaining) substrate materials, such as coco coir and vermiculite. Manure-based substrates need to be pasteurized prior to use.

Manure-Based Mushroom Substrate Recipe

2 part horse poo
1 part vermiculite
1 part coco coir
Water – Enough to hydrate to 60% capacity.

I have found it effective to mix all dry ingredients into a large bucket, then add boiling water until the dry ingredients are hydrated. Although not the most precise, you may test the capacity of the material by squeezing it. You want to be able to only get a drop or two out of the material when squeezing it hard. If too moist then add vermiculite, if too dry, continue to add water and mix.

Pasteurizing manure-based substrates

One of the easiest ways to pasteurize manure substrate is to fill a large (thick-walled 4mil) Ziploc bag, or large mushroom grow bag with the hydrated substrate. Fill a large enough pot about halfway up with water and place it on the stove on high. Gently drop your bags of substrate into the water. Wait for the water to reach a temp of 170 deg F. Let sit for 3 hours. It is recommended that you use a thermometer in order to check the internal temp of the substrate. This one works very well.

Do you have a substrate recipe you would like to share? Did we miss something? We would love to hear your comments.