Spawn Magic

Mushroom Spawn Bags 101

We were inspired to dedicate this article exclusively to mushroom spawn bags, as some of the terms used in mushroom cultivation might appear daunting to novice cultivators. But what exactly are these bags? What lies within their confines? Fasten your seatbelts and get ready for a comprehensive journey through the necessary mushroom-growing components.

What Is a Mushroom Spawn Bag?

Establishing the concept of a spawn bag marks a robust initial stride in comprehending the essential elements of mushroom spawn bags. Referred to alternatively as mushroom grow bags, these items play a crucial role in cultivating substantial quantities of mushrooms within a confined space.

Constructed from sterile plastic materials, these bags are usually equipped with a filter port to facilitate the exchange of pristine air with the mycelium. Certain variants of these growth bags even arrive pre-packed with the untainted growing substrate. Best spawn bags should possess both breathability and the ability to ease a culture injection via the inoculation port.

Check our article on How To Make Sterilized Grain on your own!

What Are the Features of a Mushroom Spawn Bag?

Spawn bags feature a gusseted design, characterized by inward-folding sides. Additionally, these bags are autoclavable, designed to withstand the high pressure and temperatures within an autoclave or sterilizer. This heat resistance is vital as growers introduce spawn bags into pressure cookers. To prevent any issues with melting, the majority of spawn bags are crafted from polypropylene material.

Moreover, spawn bags serve as effective vessels for containing grains during the sterilization process. Positioned at the forefront of the bag is a filter patch, ensuring a steady inflow of fresh air for the culture while effectively warding off contaminants.

What Can Mushroom Spawn Bags Be Used For?

Spawn bags can be used for multiple different things. They can serve as a valuable tool for generating ample quantities of primary-generation grain spawn within preliminary test batches. These bags can also be used as a fruiting chamber, creating a humid dome good for the mushrooms fruiting phase. That’s not all, they can also be recycled and reused!


When creating an initial generation of grain spawn many people opt for mason jars which is okay. However, grain spawns will find greater efficiency when used in grow bags. Opting for a grow bag as your spawn vessel offers the advantage of effortless breaking and mixing of the spawn. This will accelerate the colonization process. Additionally, using grow bags for your spawn can also simplify the task of evenly distributing your spawn onto a bulk substrate.

Read our article How To Make Mushroom Grain Spawn on your own!


Don’t forget that these bags are also referred to as the “grow bags,” thus it’s not surprising that they can be used for fruiting your mushrooms. The bag’s upper portion creates a humid shelter, encouraging mushroom fruiting. It’s important to bear in mind that the interior of the bag might not receive a substantial quantity of fresh air.

Hence, if you choose to employ the bag for mushroom fruiting, it’s important to regularly open the bag’s top to ensure proper fresh air exchange. However, exercise caution and refrain from opening the bag until the block within is fully colonized, as premature opening could lead to contamination.


Truth be told, the best practice is to start your mushroom-growing journey with new spawn bags. However, they can be repurposed for other tasks if they have not been cut open for the fruiting phase. They can be used for pasteurizing casing layers or even the substrate.

While spawn bags can be repurposed, keep in mind that their structure will degrade over time and the filter patch will also become ineffective after multiple sterilization cycles. That’s why the best idea is to start with fresh, brand-new bags.

Mushroom Spawn Bag Specifications

When choosing a mushroom spawn bag, there are a couple of things to keep an eye on, and here’s what:


Generally, the filter is designated with a micron rating, indicating the pore size of the filter itself. These ratings typically range from 0.2 microns to 5 microns. For applications involving fruiting blocks or spawn bags, it’s advisable to opt for a lower micron rating, preferably not exceeding 0.5 microns.


Spawn bags are available in a spectrum of material thicknesses, typically ranging from 2.2 mil to 4.0 mil. Bags of 2.2 mil thickness serve equally well, there is a slightly higher chance of tearing during regular handling but it’s negligible.


Mushroom spawn bags come in various sizes usually 1.5lbs and 3lbs, if they are pre-made. When choosing a ideal bag size you need to take into account things like the dimensions of your sterilization equipment as well as the grow room.

How To Use Mushroom Spawn Bags

When working with spawn bags always be in a sterile and clean environment wearing latex gloves and a breathing mask. You don’t want to mess up your substrate or the mycelium by introducing them to contaminants. Use rubbing alcohol to clean your gloves and equipment working under the laminar flow hood or in a still air box.

  • Start by unsealing your spawn bags and filling them with the substrate of your choice.
  • Place the loaded bags in a pressure cooker or a sterilizer and begin sterilizing them.
  • Allow the bags to naturally cool down to room temperature.
  • Make sure that the bags are sealed properly upon removing them from your pressure cooker or sterilizer.
  • The next step is to inoculate your bags.
  • Using a syringe inject the culture through the self-healing injection port, making sure that the needle is flame sterilized after each use.
  • Place the grow bag in a warm location with indirect lighting.
  • Regularly monitor the bag to prevent the substrate from drying out. If it does become dry, inject filtered water using a syringe.
  • Wait for the bag to get fully colonized.

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