The Beginner’s Guide to Mushroom Grow Bags

The Beginner’s Guide to Mushroom Grow Bags

Mushroom Grow Bags

Mushrooms are one of the many wonders of nature. They are incredibly versatile in their use – they can become healers, a delicious meal, or even a source of pleasure. Did you know that they are as interesting in life as they are in their birth?

Mushrooms need highly controlled environmental conditions to grow. Growers have worked hard to develop multiple methods of growing mushrooms and over the decades, they have perfected them. If you are thinking of having mushrooms at home, then you may have researched mushroom grow bags before. However, there are some important things you need to know before you immerse yourself in the world of cultivating mushrooms.

What is a mushroom grow bag? 

When people refer to a mushroom bag, they are referring to a gusseted bag or one that is folded with the sides facing inward. This is done so that the bag folds small and can lay flat. But it also opens wide enough to allow for a large amount of grain or sawdust. This bag allows for sterilization as well. This allows the cultivator to fill between the gussets, which prevents contamination from the air.


Other mushroom grow bags may also be referred to as autoclavable. This means that they can stand the high temperature of an autoclave, also called a sterilizer. This process is usually done in a pressure canner, at about 250 degrees F. It can last for many hours, especially at higher altitudes.


You may also hear the term polypropylene. This is just a material that the bag is usually made of. This material, when free from impurities, doesn’t melt unless the temperature surpasses 270 degrees F. Bags made with this material are great for holding grain or sawdust during sterilization.

Filter Patch

Finally, if you hear the term filter patch, this is just a comment on the filter that is on the front of the bag. This filter allows for mushroom cultures in the bag to get fresh air. But it won’t get contaminated by things like bacteria or mold. This filter is essential because, without fresh air, the cultures can’t grow. But if the bag is open entirely, the mushrooms could get contaminated. Spawn filters eliminate all contaminants, but fruiting filters allow greater airflow at the tradeoff of allowing some of the smaller contaminants to permeate. By the time a mycelial colony is ready to fruit, it should be strong enough to shrug off these new invaders.

Here are the 5 things you should know about mushroom grow bags:

1 - Using a spawn bag makes it easier to spread the spawn

While some people prefer to use mason jars in creating the first generation grain spawn or run a trial, these jars are not ideal for producing large volumes of spawn. Using a spawn bag allows for the spawn to be broken up easily, which helps you mix it and also speeds up colonization. 

A spawn bag is also a great way to spread the spawn to create a substrate. You can get up to 5lb or more of spawn in a large spawn bag, and this is enough to have a small log or many blocks grow mushrooms.

2 - Make sure to use filter patch grow bags for fruiting blocks

Using filter mushroom grow bags is necessary for making sawdust fruiting blocks. One bag will result in about 5lb of fruiting block. However, using this type of bag allows you to mix the spawn after inoculation. The filter patch will then promote growth, while the culture expands through the sawdust.

When the mushrooms are colonized completely, cut the top and allow them to fruit. 

3 - Some people use the bag as a way to promote fruiting

In some cases, you can promote fruiting by using the bag as a humid chamber that gets the mushrooms to fruit. In this case, there is not much fresh air in the bag, so you should open the top to allow for fresh air exchange. Don’t open it too early, though, or you may ruin colonization because of contamination.

Another method is to cut a slit between the filter patch and fungal mass. Since CO2 is heavier than air, this allows a more low-maintenance approach at the tradeoff of not being able to reuse your bag (we'll get to that in a moment). Be sure to wrap a rubber band around your block, as his prevents micro-climates that induce side-pinning. It's a common misconception that light is the strongest trigger for pinning, the strongest triggers are actually air and humidity, with light playing a relatively minor role. Fungi has more in common with animals than with plants, so while it will detect light, it doesn't seek it out as voraciously as it seeks optimum climates.

Keep in mind too, that some mushrooms grow very differently, so you should do some research to see what to expect. 

4 - You can reuse your grow bag

If you are making fruiting blocks or spawn bags, you may want to use brand new mushroom grow bags. However, you can usually reuse your bags. Our warranty only covers the initial use, but some customers can get a half dozen or more sterilization cycles. The key if using a pressure cooker is low and slow, you want the heat to be just barely high enough to maintain 15psi relative to your altitude, and be sure to add plenty of water. Rapid temperature fluxuations are very harmful to all materials at the atomic level. Spawn bags can be used to pasteurize the casing layer without exposing to sterilization conditions by simply setting it in a pot of hot water on the stove. It may rise to the top, so consider using something heavy to hold it down. Pasteurization doesn't kill all microbes, but it's "good enough" if you have a non-nutritive substrate that would take a while for an invader to get established.

You can also use these bags to make straw logs, in which they can replace the tubing. Simply fill the clean bag with pasteurized straw and grain spawn, which is just what you would do when growing mushrooms on straw.

5 - The filter size matters

If you are new to buying mushroom grow bags, you should always take a close look at the filter. You can find the filter size on the bag denominated with a micron rating, which is just a way to describe the pore size. Sizes range from 0.2 to 5 microns and beyond.

When you use the bags for spawning blocks, choose a small micron, as this protects the grain from contaminants. A bigger size allows for more air exchange, so it can easily lead to contamination in a high nutrient environment. However, if using a non-nutritive substrate such as straw, sawdust, wood pellets, coir, or others, the inoculated spawn should have no trouble overpowering any baddies that passes through the filter.

Time to find your grow bag!

You now know all about mushroom grow bags, from how big to what material they are made of, so you can’t make a bad choice. But to help you out even more check out our stock at Unicorn Grow Bags. We’re not just everybody’s favorite mushroom grow bags; we’re the industry leaders and innovators. You’re getting the unicorn without the entire stable.

Learn more about our Biodegradable Bags

Don´t forget to take a look at our different products, you are going to love them: 


Spawn Bags

Fruiting Bags

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