Important Things to Know About Mushroom Substrate

By Eve Simmons •  Updated: 04/13/21 •  13 min read

Substrates are extremely important for growing mushrooms successfully. Just like soil is essential for plants to grow, mushrooms require substrates for nutrition and swift growth.

As different types of soils have different properties which makes them suitable for particular types of plants, there are different types of mushroom substrate, too.

In this article, you will learn everything you need to know about mushroom substrate, such as the types of substrates, the materials used for making homemade substrates, and the benefits of individual mushroom substrates.

What Is a Mushroom Substrate?

Any material which helps mushroom mycelium to take root and grow is a mushroom substrate. The substrate is meant to provide the mushroom with nutrients, energy and moisture required to grow and flourish.

There are different kinds of substrates that different growers use, depending on the species of mushroom being grown and their own preferences. So, it is essential to match the correct substrate with your mushrooms so that they have the best chance to grow successfully.

Important Things to Know About Mushroom Substrate

Substrates need to be prepared before they can be used with mycelium or mushroom spores.

Water is a common additive because it can easily combine different extra nutrients. Once the substrate is ready, it will need to be pasteurized or sterilized. This is necessary to remove any competing bacteria or mold from the substrate so that the mushroom has a monopoly of growth.

Substrates for mushrooms can be stored in various types of containers. Commercial mushroom growers usually pack substrate in large plastic bags. On the other hand, home growers usually prefer to pack their substrate in mason jars or other similarly small containers.

When your substrate is prepared after effective pasteurization or sterilization and placed in a container, you can inoculate mushroom spores and start the growth cycle. If you see the mycelium growing and spreading, or signs of colonization, that means that your mushroom substrate is working like it should.

It might be several weeks, or even a few months, before the mycelium starts decomposing the substrate and spread throughout. Once the colonization stage is completed, the mycelium should cover the entire substrate surface. This is a sure sign that it is ready to fruit and flourish.

How to Make Mushroom Substrates

Mushroom substrates can be made using several commonly-found materials. Some of these substrates are widely used and effective while others are still in the experimental stages. Let’s take a look at some of the most common materials which can be used to make mushroom substrate:

Straw

Straw is an extremely inexpensive but highly effective material which can be used to make substrates for growing mushrooms. You can simply walk into the nearest farm store, or in stores that sell animal bedding or feed. Some growers have successfully experimented with corn stalks as an alternative.

You can choose to grow mushrooms in a substrate which is made purely of straw, or you can choose to add supplements that enhance the substrate’s nutrient properties. There are several ways to make mushroom substrate using straw. For instance, you can use chemicals like calcium hydroxide or peroxide. Or, you can choose to ferment the straw for a

week or so.

However, we recommend using the heating method as it is quick and eco-friendly. To do this, you need to cut the straw into 3 or 4-inch pieces. You can use a weed wacker to cut larger quantities of straw more efficiently. Once the straw is shredded, it is time to pasteurize it.

Small quantities of straw can be pasteurized by filling it in a pillowcase and heating in water boiling on a stove top at 160 degrees F, for an hour. For large quantities of straw that need to be pasteurized using the heating method, you can choose a large 55-gallon drum and heat it in water over a butane burner.

Once done, the water needs to be squeezed out of the straw so that at the time of growing mushrooms, only a few drops of water remain in the substrate. That’s it, and now your straw substrate is ready to be inoculated with mushroom spores.

Coffee Grounds

Ground coffee beans are also an excellent material to make mushroom substrate. Many expert growers have been successfully growing mushrooms in coffee grounds substrate for years now.

The best part of the deal is that you can find ground coffee beans anywhere, at home or at your closest coffee shop, which they offer for free. Another additional benefit is that the coffee grounds are already brewed in hot water so there is no need for special sterilization or pasteurization.

Coffee grounds as mushroom substrate are also one of the most efficient ways to grow mushrooms. All you need to do is mix 1 kg of dried coffee grounds with 100 grams of mushroom spawn. Alternately, you can choose to enhance the productivity of the substrate by mixing around 20% straw so that it has improved air exchange and higher colonization speed.

Hardwood Pellets

Hardwood trees, such as beech, oak or maple are incredibly effective as mushroom substrates for various species. However, pellets or sawdust from softwood trees should be expressly avoided as they make for poor substrate material.

Hardwood pellets are commonly used for pellet grills and stoves and you can easily buy them at any hardwood stores around you. Hardwood pellets are inexpensive and you can usually buy a 40 pound bag of hardwood pellets for around US$ 5.

For a 10 pound block of hardwood substrate, you will need around 10 cups of hardwood pellet and 2.8 liters of water. There is no need to sterilize or pasteurize hardwood pellets as the process of turning sawdust into pellets works to sterilize them effectively.

Many expert growers recommend alternating hardwood sawdust with bran. As wood cannot carry all essential nutrients required to grow healthy mushrooms, so there are times when you might need to add or supplement another material to the hardwood pellet substrate. To do this, you can add 2 ½ cups of oat or wheat bran or even soybean hulls.

However, if you choose to add bran then you will need to pasteurize or sterilize the hardwood pellet mushroom substrate. Numerous growers who add soybean hulls as an additive in this substrate refer to it as the “Master’s Mix” because of the surprisingly good results it gives.

Coco Coir and Vermiculite

Coco coir is made by grinding coconut husks and shells. You can easily buy it from any gardening store. Vermiculite is a brownish-yellow mineral which is useful for retaining moisture and can also be bought at any gardening supplies store. When you mix the two, it can make an incredibly effective mushroom substrate.

Making a standard coco coir brick (weighing around 1.5 pounds) requires adding around 8 cups of vermiculite into 16 cups of boiling water. Soak the mixture in a 5-gallon bucket for around an hour. Next, mix everything and put the lid on the bucket and allow the mixture to cool for around 4 hours before inoculating it with mushroom spawns.

Keep in mind that coco coir retain immense amounts of water and can expand as much as 5 to 7 times when you add water. So don’t be surprised when you find more substrate than you initially expected.

Logs

Yes, you read that right. Solid pieces of wood can also work excellently as mushroom substrates. Logs have been found to be one of the best substrates to grow shiitake and other mushroom varieties. You can use logs from most hardwood trees, such as elm, birch, oak, maple, poplar or beech.

The ideal length of log for making substrates for mushroom growing is around 3 to 4 feet with a diameter of at least 4 to 6 inches. Try to avoid using dead or dying hardwood logs as there are chances of other fungi already having colonized it which makes it harder for mycelium to flourish.

You should also avoid freshly cut logs as the tree’s natural fungi-preventing properties are active for some time after being cut. The best type of hardwood log for mushroom substrate is a clean and dry log that can be easily inoculated. Inoculating logs require drilling a series of holes using a 12 mm drill but at 4 to 6 inch intervals along its length.

Make sure to keep a distance of at least 2 to 3 inches between each row of inoculation holes in the log. Simply stuff the mycelium into the holes using a plug spawn. A plug spawn is a small piece of wood dowel which is already colonized by mycelium and is used by hammering them into holes like pegs. The holes are then sealed with wax to prevent contamination.

Manure

Although manure is regularly used in the agriculture industry it is not considered ideal for growing mushrooms. However, there are several varieties of mushrooms, including the common button mushrooms that are known to grow incredibly well in a manure mushroom substrate.

You can choose to use either cow, chicken, horse or any other type of natural manure. Usually, it requires adding two parts manure with one part coco coir. Next, water is added to reach field capacity, which is the amount of water the substrate can hold without the water dripping down from the bottom. Ideally, when you squeeze the manure substrate lightly, no water should come out.

You will need to sterilize the entire mixture before it can be introduced with mushroom spawn.

Cardboard

Cardboard is yet another commonly found material which makes for a great mushroom substrate. It is also considered one of the best substrates for beginners to grow mushrooms.

It is incredibly cheap and can be found at home or at any departmental store and super market. Cardboard substrate works well because it retains moisture easily and the corrugation allows for excellent air exchange.

Several mushroom species, such as oyster mushrooms and other similarly aggressive species, grow incredibly well in cardboard mushroom substrate. For best results, we recommend adding a supplement, such as coffee grounds, for more effective and quick growth.

How to Sterilize or Pasteurize Mushroom Substrates

Apart from knowing how to choose the right type of material, it is also important to know when is the right time to sterilize or pasteurize it to make an excellent mushroom substrate. Forget the forbiddingly expensive clean-rooms with negative air pressure, you can prevent contamination by using simple, yet effective, sterilization or pasteurization techniques.

Put simply, keeping the surfaces clean by using a 70% isopropyl alcohol solution during inoculation is an excellent way to sterilize or pasteurize your mushroom substrate.

If you are wondering about the difference between pasteurization and sterilization you should know that there isn’t much difference. Both processes are aimed at removing contaminants, such as bacteria or fungi, using intense heat; but the main difference between the two is the level of heat used.

For sterilization, the substrate material needs to be heated at around 250 degrees F while pasteurization requires heating the material at temperatures hovering around 185 degrees F.

Sterilizing Substrates

To sterilize a mushroom substrate, you will need to expose the material to temperatures higher than 250 degrees F and also keep it under pressure. The sterilization process helps to remove all contaminants that might be currently living, or lying dormant, in the substrate material.

For best sterilization, it is highly recommended to use a pressure cooker or similar device so that you can heat up the material and apply sufficient pressure at the same time.

Pasteurizing Substrates

Pasteurization of mushroom substrate requires treating the material to heat between 150 and 185 degrees F, using either steam or a water bath. This process helps to noticeably reduce the level of contaminants in the substrate material.

Although this process is not successful in removing all contaminants, it can definitely bring down the level of contamination within acceptable levels, which do not hinder the growth of mushrooms.

The simplest and most common way to pasteurize mushroom substrate material is to soak, or submerge it in boiling water for at least a couple of hours. Experience tells us that pasteurization is sufficient to remove risk of contamination of mushroom spawns.

Why Are Sterilization and Pasteurization Important?

Sterilization or pasteurization are meant to lower bacteria and mold in the substrate so that the mushroom spawn has the best chance of growing and flourishing. The substrates which support mushroom growth are moist and filled with the specific nutrients that are required for excellent growth.

Although this makes the substrate an ideal environment to grow in, it also acts as an ideal breeding ground for other fungi and bacteria, too.

Mold and bacteria grow faster than mushroom mycelium, and if left untreated, these contaminants can take over the substrate entirely. Hence, sterilization or pasteurization processes are important because they provide the mushroom mycelium with the much-needed head start to grow and flourish successfully.

Just like weeding is essential for agriculture, sterilization or pasteurization processes are essential to remove contaminants that hinder the natural growth of mushroom spawns.

How to Find the Best Substrates for Different Types of Mushrooms

As mentioned earlier, different types of substrates are suited for different types of mushroom species. If you have been wondering about an all-round substrate, then there is no definite answer to this. This is because there is no single substrate which suits all species of mushrooms.

Certain mushroom species, such as the oyster mushrooms, are naturally aggressive and can grow and colonize almost any substrate material. While some mushroom species grow well in wood-based substrates, there are still some species, such as truffles, that are incredibly hard to grow in a commercial environment.

Important Things to Know About Mushroom Substrate

Let’s take a closer look at the different types of substrates and the species of mushrooms they support:

Straw

Straw lacks several nutrients and is not ideal for growth of many mushroom species. Some of the select, strong species of mushrooms that can grow on straw mushroom substrates are:

Logs / Sawdust

Some of the most renowned varieties of mushrooms that grow excellently in wood-based substrates, such as those made from hardwood logs or sawdust, include:

Manure

Although many might think that manure would be an ideal growth substrate for mushrooms, the reality is not so. Still, there are several strong species which manage to grow well on manure-based mushroom substrate, such as:

Coffee Grounds

There are only a handful, yet incredibly popular, species of mushroom that manage to grow and flourish in coffee ground mushroom substrate, including:

Conclusion

Mushroom substrates are incredibly important to ensure optimal and strong growth for commercial mushroom growing.

Growers use a variety of materials for making mushroom substrates, including coffee grounds, manure, cardboard, hardwood logs, sawdust, and even straw. It’s important to remember that different types of substrates suit different species of mushrooms.

To ensure that your mushroom farm prospers and flourishes, make sure to choose the right mushroom substrate depending on the species of mushroom you wish to grow.

Good luck!

Eve Simmons