The King Trumpet mushroom (Pleurotus eryngii) is known for its robust, meaty texture and umami flavor. Unlike its cluster-forming oyster relatives, this fungus grows as a distinct individual with a thick, edible stem and a small cap. Cultivating this species at home allows the grower to control the environment to maximize the development of its desirable stalk. This guide provides a detailed, phase-by-phase approach to successfully growing King Trumpet mushrooms from preparation through harvest.
Essential Supplies and Substrate Selection
A successful King Trumpet harvest requires selecting the correct initial materials and growing medium. The fungal culture can be introduced via grain spawn or liquid culture. Grain spawn is often preferred by new growers because it is easier to handle and inspect for contamination. Liquid culture, a nutrient-rich solution, offers faster colonization times but requires a higher level of sterile technique during injection.
The preferred nutritional base for Pleurotus eryngii is supplemented hardwood sawdust, mimicking the mushroom’s natural woody habitat. A standard blend is the “Master’s Mix,” consisting of 50% hardwood sawdust and 50% soy hulls by dry weight, or 90% hardwood sawdust supplemented with 10% wheat or rice bran. Nitrogen-rich bran is necessary because pure hardwood sawdust has a high carbon-to-nitrogen (C:N) ratio. The mycelium requires a lower ratio, between 30:1 and 50:1, to support vigorous growth.
Necessary equipment includes autoclavable mushroom grow bags or mason jars to contain the substrate during sterilization. A pressure cooker or autoclave is required to sterilize the supplemented substrate completely, eliminating competing microorganisms. Basic measuring tools and a method for maintaining a sterile inoculation environment, such as a still air box (SAB), complete the initial supply list.
Inoculation and Managing the Colonization Phase
Preparing the substrate involves hydrating the mix to “field capacity,” where the material is moist but no water can be squeezed out with a firm press. Once hydrated, the substrate must be sterilized by placing the sealed bags or jars in a pressure cooker. Heat them to 15 PSI (pounds per square inch) for a minimum of 90 to 120 minutes. This high-heat, high-pressure treatment kills all existing microbes, ensuring the mycelium faces no competition.
After sterilization, the substrate must cool completely to below 80°F (27°C) before the introduction of the culture. Inoculation, or “spawning,” involves mixing the grain spawn into the sterilized substrate at a rate of about 10% to 20% spawn-to-substrate ratio by volume. This process should be performed inside a still air box or near a HEPA filter to minimize the risk of airborne contamination.
The inoculated bags are moved to an incubation environment for the colonization phase. The ideal temperature for Pleurotus eryngii colonization is a dark, warm environment maintained between 70–77°F (21–25°C). During this stage, the mycelium (the white, root-like structure of the fungus) rapidly colonizes the entire substrate block. Colonization takes two to four weeks and is complete when the entire block is densely covered in a uniform, white fungal network with no remaining substrate visible.
Inducing Fruiting and Harvesting
Once the substrate block is fully colonized, the environmental conditions must be altered to trigger fruiting. King Trumpet mushrooms, which are cold-weather species, benefit from a “cold shock” to initiate pinning, the formation of tiny mushroom primordia. This is achieved by placing the colonized block in a refrigerator or cold room, dropping the temperature to between 40–55°F (4–13°C) for 12 to 24 hours.
Following the cold shock, the block is moved into the fruiting chamber, where three conditions are managed: temperature, humidity, and fresh air exchange (FAE). The fruiting temperature should be slightly cooler than incubation, maintained between 59–65°F (15–18°C), which encourages slower, denser growth. High humidity is mandatory for pin formation, requiring 85% to 95% relative humidity to prevent the primordia from drying out.
To promote the King Trumpet’s signature thick stem and smaller cap, the fruiting strategy focuses on manipulating carbon dioxide (CO₂) levels. Unlike most oyster mushrooms, King Trumpets benefit from a period of higher CO₂ concentration, achieved by allowing a small air space above the block in the grow bag. This high CO₂ environment signals the fungus to elongate its stem in search of fresh air, resulting in the desired dense, cylindrical stalk.
Harvesting is timed just before the mushroom cap begins to fully flatten or curl upward, when the edges are still slightly rolled under. This stage ensures the best texture and prevents the mushroom from dropping spores, which can signal the end of the fruiting cycle and reduce subsequent yields. Harvest the mushrooms by cutting them cleanly at the base of the stem where they meet the substrate block, allowing the mycelium to recover and prepare for the next round of growth, known as a “flush.”