Substrates are a quintessential part of mushroom cultivation. They are as fundamental to growing mushrooms as soil is to cultivating plants. Understanding them and how they interact with your fungi is an inherent part of being a successful mushroom cultivator.
Furthermore, understanding substrates means understanding the biology of fungi. They are so intertwined, literally and metaphorically, that they can’t be discussed separately.
While anyone can follow a recipe, familiarizing yourself with this foundational topic allows you to understand cultivation on a deeper level. In this manner, you really get the reasons behind certain cultivation practices and the important yet sometimes overlooked details needed to achieve good yields. It also allows you to improvise, troubleshoot, and constantly improve your technique, something essential to the art of growing mushrooms.
Mycelium and Substrates
Mycelium is the fungal web-like network that produces the mushrooms we wish to cultivate. Fostering its growth is a preliminary step to growing mushrooms, just like you must cultivate a plant before harvesting its fruit.
Substrates provide three essential things for your mushroom mycelium (the 3 S’s of Substrates):
- Substance: It is the primary food source for your fungus. We will talk about this in-depth, but it provides all the nutrients needed to fuel the growth of mycelium and, eventually, the mushrooms we wish to harvest.
- Setting: Beyond nutrients, it provides a suitable habitat for the growth of mycelium. This means physical, chemical, and environmental characteristics that allow your mycelium to thrive. Moisture levels, pH, and air exchange are some of the most important. Some substrates may also have secondary compounds that either inhibit or promote the growth of fungal mycelium.
- Sterility: Substrates should be free of harmful organisms that will compete with or attack your fungus of choice. While this is primarily taken care of via pasteurization/sterilization processes, the preexisting biology in your substrate may influence your chosen methodology/success.
Substrates as Substance
Mycelium acquires all its nutrients from the substrate. To do this, it exudes an array of enzymes and secondary metabolites that modify the substrate and break it down. As the substrate breaks down and nutrients become bioavailable, it grows into it and absorbs the nutrients. To think of it in a weird and abstract way, it’s almost as if the animal digestive system were turned inside out, with digestion and nutrient absorption happening externally.
Important Services Provided By A Substrate
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Carbon is the basic building block of life and provides the energy needed to fuel fungal growth. It’s the fungal equivalent of essential carbohydrates like bread, rice, potatoes, or corn in people's diet. In substrates, carbon typically occurs as lignin, cellulose, and hemicellulose, although some substrates may contain other polysaccharides.
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Nitrogen is like the protein (imagine meat, cheese, or legumes) accompanying the carbohydrate. Organisms literally use it as the building block for amino acids, which make up proteins. High quantities of nitrogen can improve yields, but since it is so “rich” it also increases the risk of contamination.
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Minerals and Micronutrients typically occur in sufficient quantities within bulk substrates but some formulas benefit from supplements containing these.
- Moisture: Typically, moisture levels between 50-60% are ideal for most substrates. Field Capacity is often recommended when you can’t measure, which is when you squeeze the substrate and only a couple of drops are released. You are better off having a substrate be a bit too dry as opposed to too wet, as this can lead to anaerobic zones that become prone to contamination.
| Bulk Substrates | Approximate C:N Ratio | Contribution |
|---|---|---|
| Rye Straw | 80:1 | These are the primary bulk substrates used for cultivation. Their most crucial nutritional contribution is the high quantities of carbon they provide. As you can see in the table, their quantities of nitrogen vary. |
| Wheat Straw | 80:1 | |
| Oat Straw | 70:1 | |
| Rice Straw | 70:1 | |
| Sawdust | 300:1 - 500:1 | |
| Sugar Cane Bagasse | 70:1 | |
| Fuel Pellets | 300:1 - 500:1 | |
| Agricultural Waste | - | |
| Coco Coir | 100:1 | Coco Coir and Peat Moss are typically used for mushrooms cultivated in monotubs. While they provide some carbon, they primarily act as a suitable growth medium for fruiting the mushrooms. In some cases, they are also utilized in “casing layers.” |
| Peat Moss | 60:1 | |
| Supplements | ||
| Wheat Bran | 15:1 | These supplements provide an additional source of nitrogen, which can significantly improve yields. The thing to consider is that higher quantities of nitrogen mean higher risks for contamination and the need for more sterility and aseptic techniques. |
| Soy Bean Hull | 30:1 | |
| Alfalfa | 10:1 | |
| Coffee Grounds | 25:1 | |
| Gypsum | - | Provides calcium, sulfur, and other micronutrients. It also acts as a pH buffer, which can ward off contamination. They may also be used in casing layers. |
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Lime |
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| Oyster Shell | - | |
While supplementation can significantly increase yield, it also invites the potential for contamination. Many bacteria and pathogenic fungi thrive in high-nitrogen conditions; thus, growers must take extra care when utilizing supplemented substrates.
Growers with infrastructure that permits greater levels of sterility (autoclaves, laminar flow hoods, etc.) can use formulas that have up to 50% supplementation, while other growers may only utilize quantities as low as 5%.
Substrate Preferences
| Substrate Preferences by Species | |
|---|---|
| Species | Preferred Substrate |
| Oyster Mushrooms (Pleurotus sp.) |
Adaptable Oyster Mushrooms are the most adaptable of all cultivated mushrooms. They can grow on almost any substrate, including straw, sawdust, wood chips, coffee grounds, sugar cane, and all sorts of agricultural waste. Some have even experimented with growing them on cigarette butts and contaminated soils (for educational purposes). While not as aggressive, Pioppino mushrooms are one of the only species growing well on straw and hardwood substrates. Wine Caps are cultivated outdoors and grow well with both wood-chips, straw, and other organic substrates. |
| Pioppino (Cyclocybe aegerita) | |
| Wine Caps (Stropharia rugosoannulata) | |
| Lions Mane (Hericium erinaceous) |
Wood Loving Almost every other gourmet edible mushroom is cultivated on a wood-based substrate. In most cases, these are hardwood fuel pellets or hardwood sawdust. It is possible to utilize wood shavings or wood chips, but they are more challenging to work with. It is important to only utilize hardwood materials like Oak, Hickory, Cherry, Almond, Walnut, Beech, Alder, and other broadleaved trees, as most fungi do not grow too well on coniferous woods. Each species of tree will have distinct properties, so it’s worthwhile to make sure what you use is compatible |
| Reishi (Ganoderma lucidum) | |
| Turkey Tail (Trametes versicolor) | |
| Shiitake (Lentinula edodes) | |
| Maitake (Grifola frondosa) | |
| Chestnut (Pholiota adiposa) | |
| Enoki (Flammulina velutipes) | |
| Beech Mushroom (Hypsizygus tessulatus) | |
| Nameko (Pholiota microspora) | |
| Button Mushroom (Agaricus bisporus) |
Nitrogen Loving These mushrooms thrive in manure, compost, and other nitrogen-rich environments. While Magic Mushrooms grow on manure in their natural environment, modern techniques rarely utilize manure in their formulas. |
| Almond Mushroom (Agaricus subrufescens) | |
| Magic Mushrooms (Psilocybe cubensis) | |
| Cordyceps (Cordyceps militaris) |
Specialty Substrates While Cordyceps grows on insects in the wild, under cultivation, it grows on specialty grain-based media that can be supplemented with a large diversity of ingredients. |
Straw Substrate
Straw is typically utilized for the cultivation of Oyster Mushrooms. While other gourmet mushrooms can hypothetically grow on straw, the yields are low and not typically worthwhile. As mentioned in the table above, it can also work for Pioppino and Wine Caps (outdoors).
Straw ≠ Hay
Straw is a sub-product produced from the cultivation of grains like wheat, rye, rice, and oats. It differs from hay, cultivated specifically for feed and has a much higher nitrogen content. Because of this, hay cannot be used in place of straw. Sugar-cane bagasse and certain agricultural byproducts can be utilized similarly to straw.
Things To Consider When Using Straw
- Make sure the straw is fresh and properly stored before use. If it has been improperly stored and has signs of moisture or mold, it will increase your risk of contamination.
- Straw should be cut into 1-3 inch pieces. This not only makes it easier for the mycelium to colonize it, but it makes it much easier to work with. One easy way to do this is by placing it in a bucket or tote and giving it a go with a weed-whacker for a couple minutes. Alternatively, I like to use a machete and chop it against a large wood block. Some folks like to use pruning shears or a lawn mower.
- It can be beneficial to rinse the straw before using it, as it can often come full of dirt and dust.
| Pros | Cons |
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Sawdust and Other Woody Substrates
Most gourmet and medicinal mushrooms are cultivated on hardwood sawdust. This sawdust can come directly from a mill/carpenter or be preprocessed as pellets/blocks. Wood shavings and fine-particulate wood can work great as well. Woodchips can be used but take longer to colonize and often have smaller yields.
Hardwood vs Softwood
Cultivated mushrooms are almost exclusively grown on hardwoods. Hardwood refers to broadleaved trees as opposed to softwoods, which are coniferous needle-bearing trees ( consider that these classifications do not accurately represent the “hardness” of the wood).
Softwoods do not work well because they have a lot of anti-fungal compounds that prevent growth and significantly impact yield. Some growers have had success cultivating with Pine Pellets, but it is not optimal.
Note: Consider that while most hardwoods work well, they each have unique properties, yields, and affinity for certain mushroom species. We have placed the most commonly utilized and accepted tree species in bold for your convenience. |
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Hardwoods Suitable For Mushroom Cultivation
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Softwoods and Other Non-Suitable Tree Species
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Benefits of Compressed Sawdust Blocks or Pellets
Sawdust can come in its raw form, or it can come in processed into compressed blocks or pellets. While raw sawdust works well, many growers today utilize compressed sawdust because it offers many benefits to the growers. In some parts of the country, hardwood fuel pellets (HWFP) can be found at any farm store for as cheap as $5-$7 for a 50-pound bag. Unfortunately, they are more expensive and difficult to come by in other parts of the country, like the Pacific Northwest.
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Hydration: Since compressed blocks/pellets come with very low moisture levels, it is straightforward to hydrate your substrate to your desired moisture level.
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Cleanliness: When sawdust is compressed by machinery, it is exposed to high temperatures and pressure that essentially pre-pasteurizes the substrate. Many growers have success growing on unpasteurized HWFP.
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Storage: Since these materials are compressed, they take up much less room in storage and tend to be less messy. Their dense nature also means they do not absorb ambient moisture, much like loose sawdust.
- Standardized: Many growers prefer these materials because you simply know what to expect. If you’re working with a mill or carpenter, they often work with many different types of wood, and the materials may not be consistent.
Masters Mix
Masters Mix is one of the most commonly used substrate formulas for hobby and commercial mushroom growers. It is a 50-50 mix of hardwood sawdust and soybean hulls that allows you to achieve substantial yields. There are many variations on Masters Mix, with different ratios and other supplements. Some growers prefer to use bran instead of soybean hulls, and some prefer to include lime, gypsum, and other mineral additives. The recipes expert growers decide to use depends a lot on their growing conditions, methodology, and the quality/price of the materials available to them. New growers may want to start adding supplementation little by little as it increases contamination risk.
Conclusion
One of the first steps any mushroom cultivator takes is sourcing a suitable substrate for their growth. Every region has different materials available, and it might not always be as straightforward as simply picking them up at a shop. It can often take a bit of experimentation to figure out the easiest and most cost-effective substrate that still offers a high yield for your growth.
