Many mushroom species, often associated with warm, damp forest floors, surprisingly thrive in colder environments. Fungi have developed remarkable adaptations, allowing them to grow even near or below freezing temperatures. Discovering mushrooms in frosty landscapes is not uncommon, challenging conventional understanding.
How Fungi Endure Cold Temperatures
Fungi employ various strategies to survive and grow when temperatures drop. Some species produce specialized antifreeze proteins (AFPs) that prevent damaging ice crystals from forming within their cells. These proteins bind to ice surfaces, inhibiting growth and lowering the freezing point of cellular water, a process known as thermal hysteresis. Examples include Typhula ishikariensis and Coprinus psychromorbidus.
Other fungi utilize ice nucleators (INs), proteins that promote controlled ice formation at sub-zero temperatures, often between -2 and -10°C. This controlled ice formation, typically outside the cells, protects internal cellular structures from damage. For instance, Fusarium acuminatum produces ice-nucleating complexes. Fungi also adapt by slowing metabolic processes or entering a dormant state, with mycelial networks often surviving underground or within insulating substrates.
Common Cold-Tolerant Mushroom Species
Several mushroom species are known for fruiting in cooler conditions. Oyster mushrooms (Pleurotus ostreatus) include cold-tolerant varieties like the “Snow Oyster” or “Cold Blue Oyster.” The Cold Blue Oyster prefers fruiting temperatures between 1.6–10°C (35–50°F) and often requires a “cold shock” to initiate growth. These resilient fungi can even freeze and then resume growth once temperatures rise.
The Enoki mushroom (Flammulina velutipes), also known as Velvet Shank or Winter Mushroom, is another prominent cold-weather species. Wild Enoki often grow in dense clusters on dead hardwood trees throughout late autumn, winter, and early spring, sometimes pushing through light snow. Shiitake mushrooms (Lentinula edodes) also have cold-tolerant strains. After an initial incubation, they can be induced to fruit by a cold shock of around 5°C (41°F) for several days, followed by fruiting at 12-18°C (53-64°F).
Key Environmental Conditions for Cold Growth
Temperature is a primary factor, but the term “cold” for mushrooms encompasses a range. Optimal fruiting temperatures for many cold-tolerant species typically fall between 1.6°C and 18°C (35°F and 65°F). While mycelial colonization, the initial growth of the fungal network, often occurs at warmer temperatures (21–30°C), a drop in temperature is frequently necessary to trigger the formation of the mushroom fruiting body. Although growth significantly slows or ceases below 0°C, the underlying mycelium can survive freezing and resume activity when conditions become more favorable.
Moisture and humidity are also essential, even in cold environments. High relative humidity, typically between 80-95%, is crucial for mushroom development and to prevent drying. This moisture can come from consistent rainfall, snowmelt, or the inherent humidity of the growing environment. Mushrooms that grow in cold conditions often thrive on decaying wood, such as elm, oak, beech, and willow, which serves as both a nutrient source and can offer some insulation from extreme temperature fluctuations. While fungi do not perform photosynthesis, many species require some indirect light for proper fruiting, though this is less critical than temperature or humidity.