The King Trumpet mushroom (Pleurotus eryngii) is the largest member of the oyster mushroom genus, distinguished by its thick, edible white stem and small, tan cap. King Trumpets are prized for their firm, meaty texture, which holds up well during cooking, and their delicate, savory umami flavor. Their robust nature makes them a forgiving and popular choice for beginners interested in home cultivation.
Essential Supplies and Substrate Preparation
A successful cultivation begins with high-quality mushroom spawn, which is grain or sawdust inoculated with the living fungal mycelium. For indoor growing, grain spawn is often the preferred choice for beginners because it is highly nutritious and easy to mix evenly into the substrate. The substrate, which is the food source, should mimic the mushroom’s natural diet of decaying plant matter.
King Trumpets thrive on a substrate primarily composed of hardwood sawdust, such as oak or maple, often supplemented with a nitrogen source like wheat bran or rice bran for increased yield. This mixture is then packed into specialized mushroom grow bags that include a filter patch for gas exchange while preventing contamination. Before inoculation, the prepared substrate must be pasteurized or sterilized to eliminate competing microorganisms.
Sterilization, typically achieved with a pressure cooker, kills virtually all living organisms, creating a completely clean environment necessary for nutrient-rich, supplemented sawdust substrates. Pasteurization, using a hot water bath or steam, kills most competitors but leaves some beneficial microbes, a method more common for less nutritious substrates. After heat treatment, the substrate must be allowed to cool completely to below 80°F (27°C) before the next step, as residual heat will kill the delicate spawn.
Inoculation and Mycelium Colonization
Inoculation is the process of introducing the mushroom spawn into the prepared and cooled substrate block. This step should be performed in the cleanest possible environment, such as a still air box, to minimize the risk of airborne contaminants settling on the substrate. The grain spawn is broken up and thoroughly mixed with the substrate material to accelerate colonization.
Once mixed, the inoculated substrate is packed back into the grow bag, sealed, and moved to the incubation area for the colonization phase. The mycelium requires a stable, warm environment, ideally between 70–75°F (21–24°C), to grow rapidly and colonize the substrate. During this period, the bag should be kept in complete darkness, as light is not necessary for vegetative growth.
Within two to four weeks, the mycelium will spread its network of white, thread-like filaments throughout the substrate, binding it into a solid block. Successful colonization is visually confirmed when the entire surface of the substrate block is covered in dense, white mycelium, indicating it is fully prepared for the next stage. The block may also begin to shrink and feel firm to the touch.
Inducing Fruiting and Environmental Controls
The shift from vegetative growth to reproductive growth, or fruiting, requires a change in environmental conditions to trigger the formation of mushroom primordia, known as pinning. This trigger is achieved by dropping the ambient temperature to a cooler range, typically between 55–65°F (13–18°C). Simultaneously, the block needs exposure to indirect light, which acts as an environmental signal for the initiation of fruiting.
The most demanding requirement during the fruiting phase is maintaining high humidity and a constant supply of fresh air. King Trumpets require humidity levels above 85%, often reaching 90-95%, to prevent the tiny pins from drying out and aborting. Growers use a fruiting chamber, like a humidity tent or a modified plastic tub, to maintain this moisture level by frequent misting of the chamber walls.
Fresh Air Exchange (FAE) is important, as the developing mushrooms produce carbon dioxide, which can quickly accumulate in a closed environment. Insufficient FAE leads to the issue of “fuzzy feet” or long, skinny, and underdeveloped stems. To introduce FAE, the bag is typically opened by cutting a slit or removing the top section, which exposes the substrate to the air and allows for the formation of the thick, desirable stems. The frequent exchange of air, paired with the cool temperature and high humidity, encourages the successful development of mature mushrooms.
Harvesting and Post-Growth Care
Recognizing the correct moment to harvest maximizes the quality and flavor of the King Trumpet mushrooms. The mushrooms are ready for harvest when the cap has fully developed but has not yet begun to flatten out or curl upward at the edges. Waiting too long allows the mushrooms to release spores, which can shorten their shelf life and potentially introduce a bitter flavor.
Harvest the mushrooms by gently twisting them off the substrate block at the base, rather than cutting them, which can leave stubs that may attract mold. Remove all mushrooms, including any small, underdeveloped pins, to clear the surface for the next growth cycle. After the first harvest, the substrate block retains energy and can often produce subsequent “flushes,” or waves of mushrooms.
To encourage a second flush, the block benefits from a brief period of rehydration, sometimes called a cold shock, by soaking it in cold water for a few hours. The block is then returned to the cool, high-humidity fruiting conditions to trigger the mycelium to begin forming new pins. Providing consistent environmental conditions remains the best way to encourage a final harvest.