Successfully cultivating mushrooms involves managing cycles of growth known as “flushes,” where a wave of fruiting bodies develops, matures, and is harvested. The initial flush typically yields the largest quantity because the mycelium has access to the substrate’s full reserves of moisture and nutrients. Since mushrooms are composed of over 90% water, the first harvest significantly depletes the block’s hydration, triggering a rest period for the fungal network. To initiate a second flush, the grower must intervene to restore the substrate’s water content and reset the fruiting environment, mimicking natural environmental changes like heavy rain.
Post-Harvest Preparation
The moment the first flush is complete, careful preparation of the substrate is necessary to ensure the health of the mycelium and minimize contamination risk. Begin by harvesting all mature mushrooms, ensuring complete removal from the substrate surface. The preferred method for most species is a gentle twist and pull motion, which removes the entire base and avoids leaving behind decaying tissue that can attract mold.
After harvesting, inspect the substrate block closely for any small, undeveloped mushrooms, often called “aborted pins.” These must also be removed because they will decompose, creating potential entry points for competing organisms. Gently clean the substrate surface to remove any debris or spent mushroom tissue, which is a food source for molds and bacteria.
The substrate is now in a weakened state, making it more susceptible to external threats. A final inspection should look for any discoloration or fuzzy patches that might indicate early mold colonization, requiring immediate isolation of the block. Clearing the surface provides a clean slate for the mycelium to recover and concentrate its energy on forming the next wave of pins.
The Critical Step: Substrate Rehydration
The most important action for initiating a second flush is restoring the water lost during the first harvest through “dunking.” The large volume of water extracted leaves the mycelial network too dry to support the next generation of fruiting bodies. Restoring the substrate to its optimal moisture content, known as field capacity, signals the mycelium to begin preparing for the next flush.
To perform the rehydration soak, the substrate block should be fully submerged in clean, cool water, which often provides a mild temperature shock that encourages pinning. A large, clean container is necessary; while tap water is often sufficient, using distilled or non-chlorinated water can reduce the risk of introducing contaminants. Since the block will float, a weight, such as a sealed bag of water or a clean ceramic tile, must be used to keep it completely submerged.
The duration of this soak depends on the substrate type and size, but 4 to 12 hours is a common guideline for many bulk substrates. For delicate blocks like Lion’s Mane, the soak time may be reduced to as little as 20 minutes to prevent the fine mycelium from breaking apart. After soaking, remove the weight and allow the block to drain for 10 to 15 minutes to remove excess surface water that could encourage bacterial growth. The mycelium is now physiologically reset, with replenished water reserves, and ready for fruiting conditions.
Returning to Fruiting Conditions
Once the substrate block has been rehydrated and drained, it must be returned to a controlled environment that encourages the formation of new pins. The conditions maintained during the first flush—high humidity, adequate fresh air, and stable temperature—must be reinstated. The mycelium may require a slightly more aggressive trigger this second time around, as it has less available energy.
Maintaining high humidity, ideally 90% or above, is necessary to prevent the substrate surface from drying out before new pins can form. This usually involves a consistent schedule of misting the walls of the fruiting chamber, not the block directly, several times a day. The need for Fresh Air Exchange (FAE) remains high, as the developing mycelium produces carbon dioxide that must be vented to signal the fungus to fruit rather than colonize.
Increased FAE is often achieved by fanning the chamber multiple times daily or by adjusting ventilation holes. While the temperature should remain stable within the species’ ideal fruiting range, the rehydrated block may take longer to initiate the second flush, often requiring a recovery period of 7 to 14 days before the next set of pins emerges. Patience is important, as the mycelium is working to repair and reorganize its network before reproduction.
Maximizing Subsequent Yields and Longevity
The second flush provides a continuation of the harvest, but growers should be aware of diminishing returns. The second flush typically yields significantly less than the first, often producing 30% to 50% of the initial harvest mass, as the substrate’s nutrient base has been partially consumed. Subsequent flushes, such as the third or fourth, will yield even less, but they extend the block’s productivity.
To continue the cycle, repeat the post-harvest preparation and rehydration steps after each successful flush. The mycelium will continue to produce mushrooms as long as it has water and sufficient energy reserves. Monitoring the block’s physical condition is important for determining its longevity, as heavy contamination will eventually signal the end of its useful life.
If the substrate develops patches of green mold, or fails to produce new pins after two weeks following rehydration, it is likely exhausted or compromised. Contamination pressure increases with each cycle as the mycelium weakens, making it less able to defend its territory. At this point, the block should be disposed of, preferably outdoors in a garden or compost pile, where it may still produce a final outdoor flush.