Understanding the term “flush” is fundamental for successful harvesting and maximizing yields from a single substrate block. Mushroom growth involves two distinct phases: the vegetative growth of the mycelium within the substrate and the reproductive stage, which produces the visible mushrooms. A flush represents the successful transition to this reproductive stage, marking a grower’s first major milestone. Grasping this concept allows cultivators to anticipate and manage the wave-like nature of mushroom production.
The Definition of a Mushroom Flush
A mushroom flush is a collective, synchronized wave of mushroom fruiting bodies that emerges and matures over a short period. It results from the dense network of fungal threads, the mycelium, simultaneously allocating resources to produce reproductive structures on the substrate surface. This event acts as a distinct harvest cycle, where multiple mushrooms develop and are ready for picking around the same time.
The mycelium utilizes its stored energy and water to fuel this concentrated growth event. This coordinated behavior ensures the fungus releases a high volume of spores when environmental conditions are optimal. After harvesting, the mycelium enters a brief resting period before gathering energy for the next wave of growth.
Environmental Factors That Initiate a Flush
The shift from the mycelium’s vegetative growth phase to the reproductive fruiting phase is triggered by specific environmental changes. These changes signal to the fungus that it is ready to produce spores. The most significant factor is a sharp reduction in carbon dioxide (CO2) levels, achieved through increased fresh air exchange.
During colonization, high CO2 levels inside the substrate inhibit the formation of fruiting bodies. Introducing fresh air dramatically lowers the CO2 concentration, initiating the development of pinheads, the tiny mushroom beginnings. A slight drop in temperature can further encourage pinning, mimicking the temperature shift a fungus experiences when reaching the surface after a rain event.
Maintaining high relative humidity, typically between 85% and 95%, is also necessary. Since mushrooms are over 90% water, dry air caused by increased ventilation can quickly desiccate them. These three factors—reduced CO2, stable high humidity, and a moderate temperature change—must be balanced to successfully induce a strong, healthy flush.
Post-Harvest Care and Subsequent Flushes
Once the first flush is completely harvested, the substrate block requires recovery and rehydration to prepare for the next round of growth. Harvesting involves carefully removing all mature mushrooms and any small, underdeveloped pinheads. This cleaning helps reset the mycelial surface, as underdeveloped pinheads contain growth inhibitors that prevent the next flush from starting.
The most important step for subsequent flushes is restoring the water content depleted during the first harvest. Since mushrooms are mostly water, the first flush significantly dries out the substrate. Growers often perform a technique called “dunking” or “soaking,” where the entire block is submerged in clean water for several hours to allow the mycelium to absorb the necessary moisture.
After rehydration, the block is returned to the fruiting environment. While the mycelium can produce two to four distinct flushes, each subsequent flush is generally smaller in yield because the nutritional resources within the substrate are progressively consumed. With proper rehydration and environmental management, the mycelium can continue to convert the remaining nutrients into further waves of mushrooms.