Mushrooms are fungi, not plants, and rely on respiration, similar to humans and animals. This process requires them to constantly take in oxygen and release carbon dioxide as they break down nutrients for energy. Consequently, the answer to whether mushrooms need air is definitively yes, though the required amount of air exchange changes dramatically depending on their stage of development. Their need for air is less about introducing oxygen, which is always present, and more about removing the carbon dioxide they produce.
Mycelium: The Oxygen-Tolerant Network
The initial stage of a mushroom’s life cycle is the mycelium, a vast, thread-like network of cells called hyphae that colonizes the substrate. Mycelium requires oxygen for cellular respiration, which provides the energy needed to digest and spread throughout its food source. This vegetative stage, however, is highly tolerant of elevated carbon dioxide (CO2) concentrations, often found in nature beneath the soil or deep within a log. During this colonization phase, CO2 levels can safely be as high as 10,000 to 20,000 parts per million (ppm) for many species, which is significantly higher than the roughly 400 ppm found in fresh air. This high CO2 environment actually helps stimulate the rapid, dense growth of the mycelial network.
Fruiting: The Need for Fresh Air
The transition from the vegetative mycelium to the reproductive fruiting body—the mushroom—is triggered by a sharp drop in CO2 concentration. High levels of carbon dioxide act as an environmental signal inhibitor, which tells the fungus that it is still buried and should not form a cap and stem. If the CO2 level remains high, the mycelium may not form pinheads, or the resulting mushrooms will be severely deformed. The consequences of poor air exchange during the fruiting stage are often visible as “legginess,” where the mushroom develops an unusually long, thin stem and a small, underdeveloped cap. To encourage the formation of healthy, robust fruiting bodies, the CO2 level must be reduced drastically, ideally to between 500 and 1,000 ppm for most cultivated species. This requirement for fresh air, which provides oxygen and removes CO2, is known in cultivation as Fresh Air Exchange (FAE).
Managing Air Exchange in Cultivation
For successful cultivation, managing Fresh Air Exchange involves providing enough ventilation to clear the CO2-heavy air without drying out the substrate, which also requires high humidity. Since carbon dioxide is denser than oxygen, it tends to settle at the bottom of a growing chamber, making strategic ventilation important. Growers use various methods to achieve the necessary air exchange, depending on the scale of their operation.
Small-scale cultivators often rely on passive FAE, using filtered holes or vents in their containers to allow air to slowly diffuse. They may also manually fan the growing area several times a day to rapidly replace the stale air.
For larger operations, active FAE systems are employed, utilizing exhaust fans to pull air out of the grow room and draw fresh air in. Positioning the exhaust near the floor helps remove the heavy CO2, ensuring a consistent supply of oxygen for optimal mushroom development.