Creating Optimal Fruiting Conditions - Examining Air Flow

I was naive in my understanding of how easy it would be to craft the perfect fruiting conditions for my mushrooms. It's true that there are just four or five main factors to control for depending on how one looks at it - airflow, humidity, lighting, and the substrate. However, I failed to realize that there is significantly more nuance in these factors then I first realized.

In this article, let's focus on air flow. My mushrooms recently were experiencing stimmyness, elongated stems which are typically a symptom of a lack of oxygen - or correspondingly high CO2 PPM - in the air. This had occurred because I underestimated the airflow necessary for oyster mushrooms, which are particularly sensitive to oxygen levels.

Below is an image of my previous set up.

I have two grow rooms that have an 8 x 8 base and are ~7 feet high, so about 500 cubic feet. I had tubed in fresh air separately for these two grow tents but then combined the exhausts using a Y connector. Then this air was tubed through a MERV 13 filter box, which introduced further drag, before traveling along another twenty feet of tubing that went though my window and to separate the final exhaust from the air intake area - the reasoning being that I didn't want the high CO2 air output to be next to the intake area.

There were three factors working against me. First, the Y connector though it was angled so that both pipes combine nicely into the filter box, when I only turned on one fan, a decent breeze would come out of the other. This meant that the resistance from the air filter was significant and would cause the air from each fan to push into one another, reducing the amount of air going through the air filter, and ultimately out the pipe. The next factor was the air filter itself, which reduces the air throughput. Finally, I had extended the output which went up to the window formerly. But I decided to pull it out of the window about fifteen more feet to get the exhaust away from the air intake so as to not potentially mix the high CO2 exhaust with the intake air. However, this extension further introduced drag.

Given all the above, it makes sense that there was inadequate air flow in my grow rooms, and my mushrooms showed signs of stimmyness.

Here is an image of updates to the tubing:

The intake tubing remained the same, but I got rid of the Y connector so that the exhausts both have their individual piping. This gets rid of the first problem, where the air from each exhaust fan were working against one another, reducing the output through the entirety of the exhaust tubing.

As for the second, problem, this is not one that I can eliminate as I need to go through the filter box as I'm growing in a residential area. I simply bumped up the speed of the fans so that they're close to 200 CFM instead of close to 130CFM before (pre filter box drag). This ensures that even with maybe 20% drag introduced by the filter box, it would be around 160 CFM, which changes the air in the entire room once every 3 minutes, or 20 times an hour which is still maybe twice the rate needed for oyster mushrooms. This may even be overkill.

Regarding the third problem, also shortened the piping extending out of the window, so that the extra 15 feet of tubing wouldn't cause more drag - this may slightly increase the rate of CO2 PPM in the intake air coming in due to the exhaust end point and intake beginning point being close by. However, there is a breeze going through my neighborhood from south to north, so I'm not too concerned about that.

A couple other factors that I changed as well. I decided to place my exhaust fans after the filter boxes instead of before. This does a couple things. One, it allows me to place the inline fans outside of the humid grow tent ensuring that the constantly humid conditions don't damage the fans somehow. Second, the number of spores entering the fan will decrease by 90%, ensuring a longer lifetime for the fans. This is something I've realized not manner mushroom growers do. They make enough money that they can just replace the fans, but it's likely a small step that can be taken to save a little money. But I guess they make enough that they don't care.

Additionally, I had the idea to place my growing racks in between the intake and the exhaust (which are diagonal to one another - intake at the bottom corner and exhaust at the top opposing corner). My ideas was that the air would flow across the room and the fresh air would flow over the fruiting blocks, providing maximum fresh air.

However, after watching more videos on YouTube, I decided against this for two reasons. One, it might lead to more dry out of the fruiting blocks, which I don't want. And two, the racks in the middle might block the emission of the CO2 from the mushrooms. More often than not, the mushrooms racks seemed to be on the sides and not directly in the path of main air flow. Therefore, I will cede to the more experienced growers, and replicate their builds even if I don't understand it completely. Of course, a small fan in the grow room is necessary to circulate air within the tent.

Seeing how many things can influence just one of the main factors makes me realize that there is a little more that goes into growing high quality mushrooms than I first realized. I'm still only getting maybe 60% yields compared to what I should be getting. Therefore, I hope to continuously critically examine each factor until I'm at least at 80% or 90% of full yields. This would mean that for a ten pound block, which is about 3.5 dry weight, which could produce up to 6 lbs of mushroom, I would be satisfied with maybe 5 lbs of mushroom. I am much closer to maybe 2 to 3 lbs and so am not satisfied and will continue to work hard to improve yields.