The Spawn Run Explained

The “spawn run” is a critical stage in the cultivation of mushrooms, specifically in the context of growing edible and medicinal mushrooms such as oyster mushrooms, shiitake, and more. It’s a crucial step in the mushroom cultivation process, where mycelium, the vegetative part of the mushroom, colonises the substrate before the actual mushroom fruiting bodies develop. Here’s an explanation of the spawn run:

  1. Substrate Preparation: The process begins with the preparation of a suitable substrate. Substrate is the material on which the mushroom mycelium will grow. Common substrates include straw, wood chips, sawdust, or a combination of these. The substrate is often pasteurized or sterilised to eliminate competing organisms that could hinder the growth of the mushroom mycelium.
  2. Inoculation: After preparing the substrate, it is inoculated with mushroom spawn. Spawn is a substrate that has been previously colonized by the desired mushroom species. It is essentially the mycelium of the mushroom grown on a different substrate. This step introduces the mushroom’s mycelium to the new substrate, where it will grow and spread.
  3. Spawn Run: The spawn run is the phase during which the mycelium from the inoculated spawn starts to colonise the new substrate. It typically takes place in a controlled environment with specific temperature, humidity, and lighting conditions that are favorable for the growth of the particular mushroom species. The mycelium starts to spread throughout the substrate, breaking down complex organic compounds and converting them into simpler substances.
  4. Colonisation: During the spawn run, the mycelium grows and forms a network within the substrate, creating a white, web-like structure. This colonisation process can take several weeks, depending on the type of mushroom and environmental conditions.
  5. Consolidation: After the mycelium has colonised the substrate thoroughly, it undergoes a consolidation phase. During this time, the mycelium network becomes denser and more intertwined. This is an important step before fruiting can occur.
  6. Fruiting Conditions: Once the mycelium has sufficiently colonised the substrate and consolidated, it’s time to induce fruiting. This is done by exposing the substrate to specific conditions, which often include a drop in temperature, increased humidity, increased oxygen, and changes in lighting. These conditions signal to the mycelium that it’s time to produce mushroom fruiting bodies.
  7. Fruiting: As a response to the changed conditions, the mycelium will start producing mushroom pins, which will eventually grow into mature mushroom fruiting bodies. This stage marks the end of the spawn run and the beginning of the fruiting stage.

The spawn run is a critical phase in mushroom cultivation because it ensures that the mycelium is well-established in the substrate, making it more likely that the fruiting stage will be successful. The success of the entire mushroom cultivation process, from substrate preparation to harvest, depends on the health and vigor of the mycelium during the spawn run.

Tips for a Successful Spawn Run

Maintain a constant temperature (day & night) with limited (2-3 deg.c. max.), or preferably no fluctuations at all. There are 2 recommended temperatures:

For pasteurised substrates (this includes pellets – straw and hardwood based): 21 deg.c.

For sterilsed substrates (121 deg.c. / 15psi): 24 deg.c.

A stable temperature will prevent premature fruting before colonisation is complete. This is especailly important for Oyster mushrooms and Shiitake, as drops in temperature are a natural fruting trigger. If these are experienced during the spawn run then the mycelium can stop colonisation and move to the fruiting stage which leads to lower yields, fruiting within the container and possible contamination of the substrate.

Limiting light during the spawn run can help negate the above as one of the fruting stimuli is removed.