Considering Different Substrates for Mushroom Cultivation

There are different substrates for mushroom cultivation being used for various reasons. Today we look at grain, sawdust, and straw as substrates for growing

All organic material is broken down by fungi and bacteria. The job of a cultivator is to get the mycelium of the desired edible mushroom established before anything else can take hold. For the highest chance of success, the material or “substrate” needs to be prepared. Today we are looking at different substrates for mushroom cultivation. 

The word “substrate” refers to any material that is a food source for mushroom mycelium. The way the substrate is prepared will be guided by the type of substrate and the equipment that is available. Preparation includes ensuring moisture content is optimal and the substrate is clean of contaminants, mixing substrates if desired, and sometimes placing the substrate into a bag

Different substrates for mushroom cultivation include logs, stumps, woodchips, straw, sawdust, coffee grounds, grain hulls, and other carbon-rich materials. Some species are very particular about the type of substrate used, while others are flexible.

Different substrates for mushroom cultivation: Grain 

A common mushroom substrate many beginning mushroom farmers use is grain. We’ve used oats with the addition of gypsum for micronutrients and calcium for the mycelium to grow effectively. These are two substrates we’ve mainly used when we are growing out mycelium and want fast growth.

Smaller grains like millet are preferred to larger grains. By using a smaller grain like millet, the mycelium will spread more evenly and abundantly throughout the substrate. 

Grain is used as a high-nutrient medium for rapid mycelial expansion. It is typically the step after mycelial growth on agar medium. Grain is too expensive and too high in nutrients for bulk substrate fruiting, but it can be a good supplement to the sawdust or wood pellet base. It works well to boost yields by inoculating straw with large amounts of grain spawn. Grain also needs to be treated using pressurized steam and inoculated in lab conditions. It is very easy to get contamination on grain, so this is not a beginner substrate. 

Grain spawn is typically a lower generation and has a higher nutrient profile. This makes grain spawn a good option when the substrate will be further expanded or if you want to add additional nutrients into the substrate.

Understanding the “generations” of grain as a substrate

The generations of spawn are very straight forward. The first substrate inoculated from a petri plate is usually grain and called Generation 1. This is then expanded 8-10x into more grain which is Generation 2 grain. From here, farmers usually either go to Generation 3 grain or sawdust. Most growers do not perform transfers beyond four generations for fear of the strain losing vigor in fruiting -- a phenomenon called strain senescence. 


Different substrates for mushroom cultivation: Sawdust

The base mushroom substrate we use when fruiting mushrooms is sawdust. The particles are relatively small and easily consumed by the mushroom mycelium. Sawdust can be better than larger grains because of the small particle size. This substrate can often be sourced from local lumber mills. 

Two commonly-added ingredients to sawdust for fruiting mushrooms is wheat bran and soybean hull. The wheat bran is particularly added when growing shiitakes. It’s important to note that the gluten in wheat is broken down by the mycelium so that protein is no longer there. Soybean hull is often added when growing oyster mushrooms, lion’s mane mushrooms, and other species.

Different substrates for mushroom cultivation: Straw

Straw is another popular substrate, especially for growing oyster mushrooms. Oyster mushroom cultivation on straw can be broken into four parts:

  • Treatment of the straw
  • Inoculation
  • Incubation
  • Fruiting

Each step is crucial to the next and affects the overall yield. The first step is to source your straw and chop it well. Then it is time to treat the straw. By treating the straw, microorganisms are killed and competition for the available nutrients is limited. The four most commonly used methods for treating straw for mushroom cultivation include:

  • Hot water pasteurization
  • Hydrated lime
  • Cold fermentation
  • Wood ash soak

How we can help with your mushroom substrate

We provide grain spawn and sawdust spawn to mushrooms growers of all sizes so they can start growing fresh mushrooms at home. 

We do this because we understand that not all mushroom farmers have the time or equipment to produce all of their own colonized substrate. We know that some mushroom growers simply want to get to the process of fruiting fresh mushrooms. We even carry pre-sterilized grain bags for growers who want to inoculate the bag with a specific species or strain. 

Both the grain and sawdust spawn we provide are created in a sterile lab and produced consistently throughout the year, so you get contaminant-free, high-quality spawn that you can use as soon as you receive it in the mail. Our grain spawn is second generation so you can expand it out even further if you would like. 


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