Temperature is a significant factor determining success in mushroom cultivation because it directly governs the speed and outcome of fungal biological processes. Enzymes within the fungus operate optimally within a narrow temperature window; even small deviations can slow growth dramatically or cause complete failure. The entire life cycle, from the initial vegetative spread to the final production of the fruiting body, requires distinct thermal environments for each stage. Controlling the thermal environment is central to achieving a predictable and abundant mushroom harvest.
Temperature Requirements for Mycelial Colonization
The initial stage of growth, known as mycelial colonization or the spawn run, is when the fungus spreads its root-like network through the substrate. During this phase, the fungus requires stable, warm conditions, typically ranging between 70°F and 80°F (21°C–27°C) for most species. Maintaining this consistent warmth accelerates the growth rate of the mycelium, allowing it to quickly consume available nutrients. Rapid colonization is a defense mechanism, as it outcompetes bacteria and mold that thrive at similar temperatures.
While the ambient temperature should be warm, growers must also monitor the internal temperature of the substrate blocks. The metabolic activity of the mycelium generates its own heat, a process known as thermogenesis. In large blocks, this self-heating can raise the internal temperature several degrees above the air temperature, potentially creating “hot spots” that can kill the mycelium or encourage contaminants. Managing this internal heat is vital for a healthy, fully colonized substrate.
Thermal Shock and Fruiting Induction
Once the mycelium has fully colonized the substrate, an environmental change is necessary to trigger the switch from vegetative to reproductive growth, resulting in mushroom formation. This shift often includes “thermal shock,” which mimics the natural change in seasons. The shock is generally an abrupt drop in temperature, typically 10 to 20 degrees Fahrenheit lower than the colonization temperature.
A common protocol is to drop the temperature from the colonization range of around 75°F (24°C) down to a fruiting range of 55°F to 65°F (13°C–18°C). This sudden cooling, often combined with increased fresh air exchange and humidity, signals to the fungus that the time is right to produce a fruiting body. The temperature drop initiates the formation of primordia, which are the tiny structures, often called “pins,” that develop into mature mushrooms. If the temperature remains too high during this phase, the mycelium will continue to grow vegetatively without forming mushrooms, a condition known as “overgrowth.”
Diverse Needs Across Common Mushroom Species
Temperature requirements vary significantly among common cultivated species, necessitating species-specific environmental control for successful harvests. For instance, some Oyster mushroom strains, such as the Golden Oyster, prefer warmer temperatures and can fruit well in a range of 72°F to 86°F (22°C–30°C). Conversely, other species require a cooler environment to produce mushrooms.
Shiitake mushrooms generally require fruiting temperatures in the cooler range of 50°F to 65°F (10°C–18°C). Similarly, the King Oyster mushroom prefers a temperature range of 50°F to 70°F (10°C–21°C) for optimal fruiting. These differences reflect the varying ecological niches each species occupies in nature, from tropical to temperate climates.
Techniques for Maintaining Optimal Temperature
Home growers use several methods to achieve and maintain the distinct temperature targets for colonization and fruiting. For the warmer colonization phase, simple heating mats paired with a thermostat provide a steady, controlled source of warmth underneath the substrate containers. Alternatively, a small, oil-filled radiator in an insulated incubation chamber can raise the ambient air temperature without creating the drying, uneven heat of forced-air space heaters.
For the cooler fruiting phase, a different set of tools is employed to drop and maintain a lower temperature. Evaporative cooling, which uses a fan to blow air across a water source, is an effective, low-cost method to achieve a several-degree temperature reduction in a small grow space. For more precise control, a temperature controller can be wired to both a heating element and an air conditioner or exhaust fan, allowing the system to automatically heat or cool to maintain a tight thermal range.