A split or cracked mushroom caps and stems are neither contamination nor a disease. These symptoms indicate dehydration or imbalanced parameters in the fruiting chamber, which can be fixed. It can also be a genetic mutation that cannot be fixed
Split or cracked mushroom caps: main reasons and how to fix them
Split or cracked mushroom caps (stems as well) can occur in any active or edible mushroom species. Let's explore the main causes and how to address this issue.
Main causes of cracked or split mushroom caps
As you probably know, mushrooms consist of about 90% water and require high relative humidity (RH) of around 90% for pinhead initiation and fruit body growth.
The mushroom cake/block may be moist enough, but the air outside the cake/block is too dry. Usually, room RH varies from 30% to 70%. This means that for mushrooms, you need to maintain higher humidity than in your room. That's why we use fruiting chambers as closed environments with specific climate conditions for mushrooms (such as monotubs, shoeboxes, growboxes, dub tubs, plastic bottles, grow tents, and grow rooms).
🔴 Fluctuations in relative humidity (RH). The sharp difference between the required humidity (90%) and the low humidity for mushrooms (lower than 85%) causes a fast evaporation rate, moisture loss, and mushroom dehydration.
🔴 Moisture loss also occurs due to active fresh air exchange (FAE) and frequent aggressive fanning. As a result, we experience rapid moisture loss, leading to cracks on caps and stems.
🔴 Another reason for split caps is a high temperature in the fruiting chamber. In this case, yellowish pigmentations and secondary metabolites usually appear on mushrooms and mycelium.
Imbalanced or incorrect fruiting parameters can impact the development of mushroom fruit body
🔴 Lastly, cracked mushroom caps and abnormal growth can be a result of genetic factors, mutations. Some mutations are triggered by sharp changes or improper fruiting conditions. Certain genetic mutations are already present in cells (for instance, mushroom spores with genetic mutations) from the very beginning of mycelium development. Sometimes mutations look funny.
How to fix mushroom cracking
You cannot fix it if it has already happened; however, it is possible to prevent it in future flushes.
Maintain a balance between fruiting parameters
Track your fruiting parameters using a simple device (available on Amazon): relative humidity, temperature, and CO2 levels (optional).
Maintain relative humidity
To maintain high RH, use ultra-fine water mist. The Flairosol spray bottle (available on Amazon) is a cheap and effective solution for manual misting. Mist the walls of your tub! Don't spray on mycelium and mushrooms directly!
A fogger/humidifier (available on Amazon) can also be used, although it is more suitable for larger volume tubs or grow tents.
Provide gentle fresh air exchange to reduce CO2 levels
Passive natural FAE through air vents in your tub or gaps between the tub and lid is sufficient. Avoid vigorous fanning as it can dry out your cake and mushrooms.
Active FAE involves using a fan or waving a lid, while passive FAE relies on allowing air to naturally flow and diffuse
An aquarium air pump (Amazon) is a good solution for gentle additional FAE in a growbox.
If you use a fan, turn it on a few times a day for 1-2 minutes. Mist immediately after fanning.
Proper temperature for the mushroom fruiting period
Each mushroom species requires a specific temperature range for normal fruiting, and the temperature difference can vary significantly between species. For edible mushrooms, the temperature ranges from 50°F to 82°F (10°C to 27°C), while for active mushrooms, it can range from 50°F up to 100°F (10°C to 40°C).
Fresh air exchange, relative humidity, and temperature should be balanced during the fruiting period
Genetic isolation
Starting your growing journey with a spore syringe is always like a lottery. You never know what you'll end up with. Many mushroom colonies coexist, resulting in a wide genetic variety within the same mushroom cake/block.
You cannot fix genetic mutations during the cultivation process. However, you can work on genetic isolation (strain isolation, selection, cloning) to achieve perfect mushroom fruits in the future.
To sum it up
Mushroom splitting and cracking are neither contamination nor a disease. Such mushrooms are safe to consume.
However, you should check your fruiting parameters: relative humidity (should be 85-95%), temperature (check this parameter for each species), and fresh air exchange (natural FAE or active FAE with a timer and schedule).
All these factors should coincide and be balanced.
Have a happy growing and enjoy healthy shrooms!
