The King Oyster mushroom, Pleurotus eryngii, is a highly prized culinary fungus recognized for its thick, meaty stem and savory flavor. Cultivating this species at home is more challenging than growing common oyster varieties, but the resulting harvest is rewarding. Success relies on careful management of the substrate and precise control over environmental conditions during incubation and fruiting.
Substrate Preparation and Sterilization
The ideal growing medium is a nutrient-dense substrate, typically a blend of hardwood sawdust (such as oak or beech) supplemented with a nitrogen source. Common supplements include wheat bran or soy hulls, which provide the extra nutrition needed for robust mycelial growth. The final mixture should achieve a moisture content of approximately 70%, often described as “field capacity,” where the substrate is fully wet but does not release water when squeezed.
Sterilization is necessary to eliminate competing molds and bacteria that thrive on the rich substrate. For home growers, a pressure cooker or autoclave is the most effective method, heating the substrate above 250°F (121°C) at 15 pounds per square inch (PSI). This high-heat, high-pressure combination ensures that nearly all microbial life is destroyed. After the heat treatment, the substrate must be allowed to cool completely to below 86°F (30°C) before inoculation.
Inoculation and Mycelial Colonization
Once the substrate block has cooled, inoculation involves mixing the King Oyster grain spawn into the prepared medium. Maintaining a clean, aseptic workspace is important during this stage to prevent airborne contaminants from entering the nutrient-rich substrate. The spawn, typically fully colonized grain, is broken up and thoroughly distributed throughout the substrate to provide multiple starting points for the mycelium.
Following inoculation, the substrate block enters the colonization phase, also known as the spawn run, requiring a stable, dark environment. The optimal incubation temperature for Pleurotus eryngii ranges between 68°F and 75°F (20°C to 24°C). Mycelial growth is relatively slow compared to other oyster species, often taking three to four weeks for the white, thread-like network to completely cover the substrate. The block is ready for the next phase when its exterior is entirely covered in a dense, white coating of mycelium.
Inducing and Maintaining Fruiting Conditions
The transition from mycelial growth to mushroom formation requires a change in atmospheric conditions to trigger pin formation, a process called cold shock. This involves moving the fully colonized block to a cooler environment, ideally between 50°F and 70°F (10°C to 21°C). A crucial trigger for King Oysters is the introduction of indirect, low-intensity light for about 10 to 16 hours a day to regulate the growth cycle.
Achieving the characteristic thick stem requires meticulous control over fresh air exchange (FAE) and humidity. Unlike other oysters, P. eryngii thrives when carbon dioxide (CO2) concentration is managed to encourage upward stem growth rather than large caps. Adequate FAE, often requiring 5 to 10 air changes per hour, helps vent the CO2 produced by the growing mycelium and mushrooms.
The high humidity requirement, between 85% and 90% relative humidity, is maintained by misting the environment or using a humidity tent to prevent the delicate pinheads from drying out. Insufficient FAE coupled with high CO2 levels results in tall, skinny stems with underdeveloped caps. Low humidity can cause the mushrooms to crack or stall. As the mushrooms develop, the grower must balance high air exchange with elevated humidity to ensure proper structure.
Harvesting and Post-Harvest Handling
King Oyster mushrooms are ready for harvest when their thick, cylindrical stems have developed fully and the cap edges are beginning to flatten but have not started to curl upward. Harvesting before the cap fully flattens or the gills drop white spores ensures the best texture and flavor. The entire cluster should be harvested by twisting and pulling it cleanly from the substrate surface, or by cutting the stem flush with the block.
It is important to remove all mushroom tissue, including any tiny pins, from the substrate to prevent mold growth and prepare the block for subsequent harvests. King Oysters may produce one or two more flushes; re-initiating growth involves soaking the block in water for a short period to rehydrate the substrate. For temporary storage, King Oysters keep best in the refrigerator at approximately 4°C (39°F). Placing them in a paper bag or a slightly open container allows them to breathe, maintaining their firm texture and extending shelf life.