Final Flushes

Frustrated that my oyster mushrooms' second flushes were not generating as intended, this prompted a deep dive into the reasoning. A high biological efficiency (BE), as defined by % of fresh mushroom flesh over dry substrate used, is entirely dependent on excellent second and possibly third flushes.

It occurred to me that when the mycelium pins and pushes out a flush, it is as though they are giving birth. They muster all the nutrients and water in their network to form the mushrooms, which when harvested, trigger a phase of rest and recovery. The mother must rest well after giving birth. In contrast to the active growth phase which requires significant FAE for oyster mushrooms, the rest phase decreases FAE, lighting, and re-raises humidity.

Formerly, I was not letting the mycelium blocks rest well. The exposed substrate was constantly exposed to fresh air exchange which prevented the regrowth of mycelium over the dried out spot. The humidity was not re-raised to 95 - 100% to allow for maximal hydration (especially given that I am not soaking), and the lighting was not dimmed. These in addition to other factors were what prevented an excellent second flush from forming.

Let's take a look at all of the fact patterns in more detail.

1) Location and size of cut:

Previously, I was cutting a large "X" on the long side of the mushroom block. I did this for a few reasons. First, cutting on the long side allows for more stability when keeping the block on the shelf and I had seen other mushroom farmers do this. I was also replicating the large cut covering the entire surface of the long side as other farmers seemed to do this.

I switched over to a smaller "x" in the center of the long side because it seemed like it would lead to better second flushes. The cut is more equidistant from all the points in the bag (as opposed to the cut on the long side which is very far from the opposite side). Additionally, the smaller hole means that the substrate has less exposure to the fresh air exchange and there is less chance of the block drying out. So far, it seems to be giving me better yields.

2) Pinning phase

When the mushrooms start to pin, they will push open the cut that has been made to expose the mycelium to the fresh air. In the above image, the pins all form right beneath the cut and the mushrooms begin to grow out. However, the grower should exercise vigilance during this stage as sometimes loose bagging results in significant pinning in areas around the cut. The formation of these pins is wasted energy as they will press against the plastic but be unable to grow further, requiring an observant grower to increase the size of the cut. The larger cut then increases the post-harvest surface area which makes drying out more likely.

To avoid this, effort should be applied to make cuts where the plastic sticks to the substrate as closely as possible to minimize the air exposure adjacent to the cut. I have yet to come up with a satisfactory solution to this problem but some sort of rubber bands or tape could be useful to press the areas surrounding the cut into the substrate to avoid wasting energy on suboptimal pinning.

3) Harvesting procedure

I originally wrote that may be better to harvest the flush with scissors, but that adds another step and I do not think it is actually necessary as one would need to clean the debris or stump of mushroom from the substrate anyway. Instead, gently twisting and pulling with hands seems to be adequate, especially given the smaller hole size, which minimizes the substrate being ripped away.

Once harvested, make sure to scrape away any dead tissue or debris which may rot and inhibit the re-growth of mycelium and the subsequent proper generation of the second flush. Then, the bags should be re-sealed with some sort of tape. It doesn't actually have to be micropore tape - scotch tape or duck tape is fine as long as there are a few cracks for air to seep in. The goal is more limited air exchange but not none.

The sealed bags will allow the bags to better retain moisture and reduce exposure to fresh air exchange which will allow for a better rest period in preparation for the second flush.

4) Raising humidity, raising light, and lowering FAE

If all mushrooms in the same grow tent were input at the same time, the lighting, humidity, and fresh air exchange could be all changed to cater towards the resting mycelium. Unfortunately, due to space constraints, I have multiple batches of mushrooms in various stages at any given time - pinning, active growth, and resting. In order to even further facilitate the resting process, I have put an old bike cover over the rack with resting mycelium.

This tent like structure blocks out the light completely (well it doesn't go down all the way to the floor, so does let some light come in), further reduces FAE (basically negligable), and retains moisture as there is little to no FAE. So far, it seems to be working as I have examined the cut areas and there is significant regrowth of mycelium relative to what had been the case before.

Using these bike covers as mini-tents to create a micro-climate within the overall grow room allows me to keep the environment catered towards growth while also allowing for the harvested blocks to rest. I am hopeful that this and other steps are sufficient to create great second flushes without a need for soaking the blocks.

Conclusion

This is my final summary of the factors necessary to produce an adequate second flush. While I have yet to harvest a good second flush from my Italian oyster mushrooms as its only been a week or so since my awareness of this problem came up, I am quite confident that the problem has been somewhat resolved. In the following weeks, the oyster mushrooms will let me know.