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Mushroom Substrates: Complete Guide for Beginners + Easy Recipes

Mushroom Substrates: Complete Guide for Beginners + Easy Recipes

Despite their common classification as a vegetable in the culinary world, mushrooms do not belong to the plant kingdom. Rather, they are the fruiting body of a fungus and lack true roots. Nevertheless, they do have a complex network of mycelium, thin filaments that grow underground.

What is mushroom substrate? Wild mushrooms grow in soil or on decaying logs, but in commercial or home-growing operations, a mushroom substrate is used to optimize yields. These substrates are the equivalent of soil for plant production. 

A high-quality mushroom substrate can mean the difference between growing no mushrooms or having a record-breaking yield.

There are no mushrooms produced if the underground mycelium does not have the right environment to spread. 

Guide to Mushroom Substrates

Luckily for growers, there are plenty of options to use as a mushroom substrate. All these options can confuse new farmers because there are so many options to choose from. We will break down everything you need to know to choose the best mushroom substrate.

Mushroom Substrate Explained

When you are growing plants, the soil needs to contain a variety of nutrients, minerals, and organisms to create the healthiest environment. Mushrooms need nutrients, but not nearly as many as most plants.

As a fungus, mushroom mycelium ends up competing with mold and bacteria to grow. This is why mushroom growers use a special substrate that is usually pasteurized or sterilized to grow their mushrooms. 

Mushroom Substrate Purpose

The purpose of the mushroom substrate is to provide the best environment, nutrients, and water for the fungus to produce mushrooms. The mycelium needs to expand large enough and be in good condition to create the fruiting bodies (mushrooms).

Common Mushroom Substrates

For home growers, the most common mushroom substrates are cardboard, coffee grounds, straw, and hardwood pellets. All of these substrates are easy to use and need little to mild modification to be ready to grow. 

Cardboard and coffee grounds are the best options for homesteaders who are trying to be sustainable in their practices.

Cardboard can be recycled and used to produce food. You can use your coffee grounds or collect grounds from a local coffee shop to prevent excess waste from ending up in landfills.

Best Mushroom Substrate

The best mushroom substrate is known as “Master’s Mix.” It is a 50/50 mix of hardwood pellets and soybean hulls. This combination is known to produce high yields and is relatively affordable to produce.

How To Prepare Mushroom Substrate

Once you choose your substrate, you’ll need to make sure it is prepared for the mushroom spores or spawn. First off, you will add water and any additions to your mix. Amendments, like wheat bran or manure, add nutrients to your substrate.

If your substrate is not already sterilized, you will then pasteurize or sterilize it. Finally, place your substrate in the final containers and add your mushroom spores, spawn, or pieces. 

When To Sterilize, When To Pasteurize

The goal of sterilization and pasteurization is to remove living organisms, like mold and bacteria, from the substrate. These organisms compete with the fungus and can cause less or no mushrooms to grow. 

Sterilization is necessary for high-nutrient ingredients, like manure and food products (bran, soybean hulls). Pasteurization is sufficient for low-nutrient substrates like straw, coco coir, cardboard, and sawdust. 

Best Practices for Using Mushroom Substrate

  • Make sure your substrate has 1-2% nitrogen. You may need to add an amendment to get to this amount.
  • Other necessary nutrients (in small amounts) include magnesium, phosphorus, sulfur, potassium, and calcium.
  • The substrate should be slightly acidic (5-6.5 pH). 
  • The moisture content should be between 50-70%. If you squeeze the substrate in your hand, only a couple of drops of water should fall out. 

Mushroom Substrate Supplements

Supplementing your mushroom substrate may be necessary if you are using a low-nutrient medium, like straw. The kind or amount of supplement will depend on the type of mushrooms you are growing.

Most supplements are derived from grains or seeds, like wheat/oat bran or soybean hulls. Many animal feeds contain these grain-based supplements and are already pasteurized, making them a great option to use.

Mushroom Substrate Recipes

Some mushroom substrates are straightforward, like cardboard, and do not need a recipe. These are the recipes if you are using a mix that contains multiple ingredients or supplements.

Coffee Grounds

Many eco-friendly mushroom farms choose to grow their mushrooms on coffee grounds. It is easy to get free grounds from your local coffee shop (or your kitchen). The grounds are already high in nitrogen and other nutrients. In addition, the brewing process pasteurized the grounds. 

Add water to your coffee grounds until they reach the appropriate moisture content. Many growers like to add a small amount of straw to their grounds to increase the air exchange for the mycelium. When adding your mushroom spawn, use one part for every 10 parts of coffee grounds.

Vermiculite and Coco Coir

Coco coir is made from ground-up coconut husks and shells. Vermiculite is a mineral that retains moisture and aerates the mixture.

Mix one part coco coir with one part vermiculite. Since coco coir usually comes as a brick, you’ll need to add boiling water (an equal amount to the dry ingredients). Make sure the mixture cools before adding your spawn. 

Hardwood Pellets

Hardwood pellets are usually used for pellet grills and smokers. They are an affordable option that many mushrooms love to grow in. Make sure you are using hardwood and not softwood (100% oak pellets on Amazon). 

To prepare your pellets, add 9.5 ounces of water per cup of pellets. The pellets are sterilized through the production process, so they are ready to use.

Most people add oat or wheat bran to supplement the pellets (4 tablespoons per cup of pellets). Any supplements will need to be sterilized before or after being mixed with the pellets.

Manure

Some mushrooms grow very well on manure, but it is usually not the best substrate to use. Especially because it will need to be heated up and sterilized. 

To create a manure substrate, mix two parts of manure with one part coco coir. Add enough water so the mixture is moist but water is not pooling at the bottom. 

Can I Use Perlite To Grow Mushrooms?

Perlite alone is not a suitable substrate for growing mushrooms. However, it is a great addition to your mushroom substrate mix because it is sterile, retains moisture, provides aeration, and has a neutral pH. 

Can You Use Potting Mix To Grow Mushrooms?

Potting soil can be used to grow mushrooms, but it is not ideal. Supplemental ingredients, like sawdust, straw, or coffee grounds, will need to be added so the mycelium has plenty of food to consume. 

Can You Use Cow Manure for Mushroom Substrate?

Cow manure can be used to easily grow some species of mushrooms. However, for optimal use, it should be sterilized and mixed with a moisture-retention ingredient, like coco coir. 

What Are Mushroom Substrate Bags?

Mushroom substrate bags are clear plastic bags that contain substrate. There is a small port in the bag that allows the grower to insert their mushroom spawn. Periodically, the port can be used to add fresh air to the bag to promote mycelium growth. 

Where Can I Buy Bulk Mushroom Substrates?

Conclusion

If you are interested in growing your own mushrooms, it is important to build a good foundation of a mushroom substrate. This mixture can be the difference between a delicious harvest of your favorite mushrooms or a sad container of empty growing medium.