Let’s talk about contamination(s)…
Growing mushrooms is an incredibly rewarding experience, but as many cultivators know, it’s also a bit of a frustrating challenge when it comes to contamination. Spores and contaminants seem to be lurking around every corner, waiting for an opportunity to make their way into your grow. While contamination is a natural part of the mushroom cultivation journey, learning how to manage it can mean the difference between a bumper crop and a complete failure.
In this post, we’ll go over how to deal with normal contamination issues when growing mushrooms, and how you can cultivate healthy mushrooms without getting overwhelmed.
Understanding Contamination: What Are You Up Against?
In mushroom cultivation, contaminants are typically molds, bacteria, or unwanted fungi that can outcompete or destroy your desired mushroom species. Here are some common contaminants:
Green Mold (Trichoderma): This mold is infamous in mushroom growing circles. It often shows up as green patches on the substrate and loves environments that are damp and poorly ventilated.
Black Mold (Aspergillus): A more severe contaminant that appears black and can spread rapidly.
Bacterial Blotch: This looks like a slimy yellow or brownish spot on the surface of your mushrooms and is usually caused by improper humidity levels.
Cobweb Mold (Dactylium): Cobweb-like mold is common, often appearing as grayish webbing on the substrate, and usually signifies an overly humid environment.
Understanding these common forms of contamination is the first step to prevention.
1. Start with Clean Techniques
The most important rule for any mushroom grower is sanitation. Since mushrooms are delicate, contamination often occurs due to improper sterile technique. Here are some ways to improve cleanliness:
Sterilize or Pasteurize Substrates: One of the most crucial steps is ensuring your growing substrate is free of contaminants. Pasteurize (for things like straw) or sterilize (for substrates like grains) before use.
Keep Your Space Clean: Before working with your spawn or substrate, clean your workspace thoroughly. Wipe surfaces with 70% isopropyl alcohol, and wear gloves and a mask if necessary.
Use a Still Air Box (SAB): A still air box is a simple DIY tool that helps reduce airborne contaminants when inoculating or handling spores.
2. Monitor Moisture and Humidity Levels
Most contamination loves moisture—especially when it’s stagnant. It’s essential to find the right balance of moisture for mushroom growth without going overboard:
Don’t Overwater: Over-saturating your substrate can encourage mold and bacterial growth. The substrate should be moist but not dripping wet. Overly damp conditions favor competitors like Trichoderma.
Proper Humidity in Fruiting Stage: During fruiting, mushrooms need a humid environment (typically 85-95% RH), but airflow is also crucial to prevent bacterial growth. Consider using a humidity controller to help monitor levels and make adjustments as needed.
3. Ensure Adequate Airflow
Stagnant air is a contaminant’s best friend. Molds and bacteria thrive in environments where there isn’t enough fresh air exchange.
Introduce Fresh Air Regularly: Especially during the fruiting stage, make sure there is some kind of airflow. Many mushroom growers use a small fan or provide indirect ventilation.
Fan After Misting: If you are misting your grow area to boost humidity, be sure to fan afterward to ensure there’s no stagnant moisture hanging around.
4. Spotting and Isolating Contaminants Early
Early detection is crucial. Here are a few tips on how to identify contamination early and what to do about it:
Inspect Daily: Check your substrate and growing containers daily for signs of discoloration or strange smells. Healthy mycelium typically appears bright white, whereas contaminants like molds can be green, black, yellow, or gray.
Remove Contaminated Portions: If you spot a small contamination, you may be able to remove it with a sterilized knife or spoon. Make sure to dispose of contaminated material away from your grow area. Be cautious—if the contamination seems widespread, it’s better to dispose of the entire batch.
Quarantine Contaminated Jars or Bags: If you are working with multiple grow bags or jars, isolate any that look contaminated to prevent the spread.
5. Adjusting Environmental Factors
Environmental factors like temperature and humidity can have a huge impact on contamination:
Keep Temperatures in Check: High temperatures (above 27°C or 80°F) favour the growth of many moulds and bacteria. Aim to keep your growing environment in the recommended temperature range for your mushroom species. For example, many species prefer incubation temperatures around 21-24°C (70-75°F).
Humidity Control: Using a hygrometer can help ensure your grow area maintains optimal humidity levels without becoming overly moist, which can promote mould growth.
6. Choosing Resistant Species
Some mushroom species are more resilient than others. Beginners may want to start with species like oyster mushrooms (Pleurotus spp.), which are relatively fast-growing and can outcompete many common contaminants. Lion’s mane and reishi also have a reputation for being hardy compared to slower-growing species like shiitake, which may be more susceptible to contamination.
7. Proper Disposal and Restarting
If contamination becomes too widespread, it’s important not to try and salvage the batch, as this can create additional problems. Here’s what to do:
Dispose Properly: Dispose of the contaminated substrate in a sealed plastic bag and, if possible, compost it outdoors—away from your grow space.
Clean Thoroughly: Clean your grow space thoroughly with a bleach solution or 70% isopropyl alcohol before attempting a new batch. Cross-contamination can carry over if you’re not diligent with cleanup.
8. Embrace the Learning Curve
Contamination is a normal part of learning to grow mushrooms. Even seasoned cultivators occasionally deal with contamination. Each failure is an opportunity to refine your process and better understand the needs of your fungi. If your batch gets contaminated, take notes on what might have gone wrong. Was your humidity too high? Did you forget to sterilize a tool? Understanding these lessons will help you succeed in the long run.
Conclusion: Cultivate Your Skills, Not Just Mushrooms
Dealing with contamination can feel daunting, but remember that every cultivator experiences it at some point. By taking preventive steps, improving your sterile techniques, and understanding the environmental needs of your mushrooms, you can minimize contamination and grow healthy, vibrant mushrooms.
Keep experimenting, stay observant, and don’t be discouraged by setbacks. Each attempt brings you closer to your goal, and soon enough, you’ll be enjoying a harvest of beautiful mushrooms, grown entirely by you!
