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Mushrooms are the fruiting body of fungus, much like the mold you can find that consumes rotting trees, old food in the fridge, etc. Fungi are competitive. The strongest fungi present will overtake the others. This is why mushroom contamination prevention is so important, because other molds can and will overtake your mushroom growth.
Preventing contamination is a very important factor in mushroom growing. Improper handling of sterilization steps can result in the ruining of many hours of work, and it can be very frustrating. This is because as soon as you see mold growth on your mushroom substrates, you must immediately dispose of it.
Mold, aside from your mushroom mycelium, has no place in a grow and can lead to health risks if you leave it unattended.
So, now that you understand mold must be avoided, what steps can you take?
Do all mushroom grows need to be sterilized to prevent contamination?
The simple answer is yes, all mushroom substrates need to be sterile before you introduce your mushroom spores. Without proper sterilization steps, you greatly risk mold and contamination growth.
It is also the case that some mushrooms are better at fighting mold than others. Some mushrooms can have some other invasive mold spores on the mushroom growing substrate and outcompete them and colonize the substrate, but this is not common.
For this reason, you must always sterilize your mushroom growing mediums (substrates) before you attempt to inoculate them with your spores.
Do I need to sterilize mushroom substrates outside?
An important sub-topic to address is growing mushrooms outside. Many people enjoy growing mushrooms outside because they may only have space outside to grow, so they can grow a lot at once. Some mushrooms also just prefer the outside, depending on the climate of the region you live in.
Sterilizing mushrooms for outside grows helps, but it is not as necessary. Outdoors, you are gambling that molds or other contamination won’t take over your mushrooms and outcompete them.
Mold and mushroom spores alike float threw the air and land on material that they then grow on and colonize. You can only do so much to prevent contamination outside.
Sometimes your mushrooms will successfully grow, other times a natural mold that travels through the air will reach your grow and take it over.
There isn’t much you can do defend against this, other than grow many sets of mushrooms at a time. If you do plan to grow mushrooms outside, we recommend doing about as much as you can. For example, if you are growing mushrooms outdoors using logs, try to do about 5-6 logs. This improves your odds of having at least some surivive potential contamination.
We recommend sterilizing your growing medium as you normally would, then placing it outside for the colonization stage and hope for the best!
Sterilization steps for preventing mushroom contamination
The basics of sterilizing mushrooms consists of a few simple steps, depending on what type of container you are actually growing your mushrooms inside of.
P.S. Read more about mushroom contamination prevention in this article from Fresh Cap here.
Sterilizing Mason Jars for Mushroom Growing
If you are going with a small, beginner grow setup, chances are you are probably using mason jars to grow mushrooms. These are a great introduction to growing mushrooms, and they are very easy to sterilize.
You simply fill your mason jars with your growing medium and make sure there are holes punctured in the lids so that you can inject spores after sterilization without having to open the jars.
Then, cover tightly with tinfoil and pressure-cook the jars for about 90 minutes and the process is complete. Let them cool down, and your contents are sterile.
Read more about the steps involved in sterilizing mason jars for mushroom growing here.
Mason jar growing also involves a dry material layer on the top of the mushroom substrate. This prevent mold from being able to grow on your substrate, because mold needs moisture. By using a dry protective layer, you reduce the chances of mold greatly.
Sterilizing Mushroom Grow Bags
Oftentimes, mushroom grow bags will arrive pre-sterilized. This means you don’t need to sterilize the contents of the bag again, you can simply inoculate with your mushroom spores and it’s done.
If you make your own mushroom grow bags, then it’s important you sterilize the contents. You either need to pressure cook your mushroom substrate, just like above, or you can fill your mushroom growing bags with the substrate, seal them up, then sterilize.
Make sure if you are going to sterilize mushroom growing bags that they are ‘autoclavable’ bags. This means that the bags can withstand high-heat environements and won’t melt. Otherwise, do not attempt to steam-sterilize a bag that is not safe for it.
Read more about growing mushrooms in bags here.
Sterilizing Buckets and Other Grow Containers
You may not be using mason jars or mushroom growing bags, in which case you will simply sterilize the mushroom substrate, whether it’s straw or soil, and then place it into your containers. Then, you will inoculate with spores and hope for the best.
This is because oftentimes other containers such as buckets are too big to sterilize as a whole. You have to sterilize the contents separately, then add it to the bucket, tray, or other container.
sterilization of substrate, clean inoculation, still air box, dry later to prevent growth, using jars/bags/other sealed things
outisde, not much can be done, use raised boxes and grow many at a time to prevent contamination
How to prevent mold and contamination in mushroom growing
Now that you understand the basics of sterilization, it’s important to understand the ways you can prevent contamination during the colonization and growing phases.
Make sure you fully sterilize your grow medium in the first place as shown in the steps above, so there’s no chance of issues from that.
As your mushroom mycelium is growing, it is colonizing the mushroom substrate slowly, so there is still a risk of mold contamination throughout this process.
Sterilizing your inoculation needle
In general, once the sterilization process is done make sure that you are working on your grow in sterile conditions. This means always wash your hands, and sterilize any equipment you are using.
This includes your needle for spore inoculation. You will want the metal needle to be sterile before putting it inside your mushroom substrate. You can do this with alcohol or a flame, to heat up the needle enough to sterilize the needle.
Contamination from outdoor air
Try to also work in a clean space. If you are working with your substrate outdoors or in an area with a lot of air from outside flowing in, you risk contamination. This is because mold spores flow through the air, and can easily land on your equipment, hands, or mushroom substrate, contaminating it.
Read more about sterile working conditions in this guide here.
Secondly, while your mushrooms are still colonizing the substrate, don’t open the bags or jars, they should not be exposed to fresh air. Only expose your mushroom substrate to fresh air once you are ready to engage the frutiing stage, because at that point the mushroom mycelium is s strong enough to not get moldy.
Preventing contamination using mushroom grow bags
We highly recommend eventually graduating to mushroom growing bags as your primary container for growing mushrooms. They are very sterile and easy to use. There is a reason why so many growers stick with grow bags as their main growing storage material.
Plastic is inherently sterile and has many sterile uses in the world beyond simply mushroom growing.
We have a whole guide on using mushroom grow bags here.
Conclusion
There are a lot of steps you can take to prevent mushroom contamination while growing mushrooms. Always sterilize your medium where applicable, and don’t rush the sterilization process. Contamination can ruin days or even wweeks of hard work.
Secondly, try to reduce outside contamination to your mushroom growing until it’s time to fruit. Keep sealed bags and jars closed!
If you are growing outside, contamination is simply a fact of life. So, try to grow a bunch of mushrooms at once so at least some may work out successfully.
Have fun and happy growing! Back to mushroomgrowing.org.
