A shotgun fruiting chamber (SGFC) is a simple fruiting chamber used for providing both fresh air and humidity to fruiting mushrooms.
The setup is easy to build and should only take an afternoon to complete.
This post discusses how to build a shotgun fruiting chamber but also the theory on how a shotgun fruiting chamber works, I would advise reading both of these sections in full to understand the theory about how it works, this will help to avoid common mistakes with its setup.
What Is A Shotgun Fruiting Chamber?
A shotgun fruiting chamber is essentially a large tote which is filled with around 4 inches of perlite with holes drilled, 2 inches apart, on all sides. The perlite is soaked with water to provide a high humidity environment to the fruiting mushrooms placed inside.
How To Build A Shotgun Fruiting Chamber.
Estimated Time to complete 2-3 hours.
Although straight forward, building a SGFC can take a few hours, I was careful not to rush the drilling as there is a risk of cracking the plastic box so I made sure to take an afternoon to complete the build carefully.
Requirements
- 50L plastic tote: First and foremost start with a suitable sized plastic tote, try to get as large as possible, a 50 litre / Quart transparent tote is probably the smallest a SGFC should be otherwise the system described above wont work.
- Perlite: This is a volcanic glass that, when heated, expands and becomes very porous. You'll need enough to fill the bottom of your tote with about 4 inches of perlite.
- Drill: Needed for making holes in the tote.
- ¼ inch Drill Bit: This is used with the drill to create the necessary air and gas exchange holes in the tote.
- Piece of wood (this will avoid cracking the box).
- Measuring Tape or Ruler: To ensure even spacing of the holes.
- Sharpie or Marker: To mark where you will drill the holes.
- Water: For soaking the perlite to maintain humidity inside the chamber.
- Hygrometer (optional): To monitor the humidity levels inside the chamber. I don't really find these useful however.
Mark out the holes (30 minutes).
First thing you need to do is mark out holes on every side of the box, 2 inches apart. Start at the top, place a measuring tape along the box and move along in a horizontal manner marking out a hole every 2 inches along.
Once that line is completed begin a new line 2 inches below this one.
Continue until every side is marked like this.
Dill Holes in Tote (1 – 2 hours).
Drill a hole where each one of the marked holes is with a ¼” drill bit. This can take a while but don't rush this or you risk cracking the box.
Tip: Use a piece of wood to reinforce the plastic box while you drill through it, this will allow you to add more pressure and get the holes drilled faster.
Cleaning and Preparing the Tote (30 minutes).
Now that you have drilled the holes there will be a lot of malformed edges inside the shotgun fruiting chamber, so use a Stanley knife to trim these edges down.
Next hoover up any excess plastic and dust left inside (or outside) the tote and then give it a wipe down again to remove any other debris.
Fill With Perlite (10 minutes).
Prepare the perlite by filtering it through a sieve to remove very small particles, these particles can block up the fresh air exchange holes if they are not removed so make sure to get as many of them out of the mix as possible. On the photo below you can see the very fine dust I have removed from the mix.
Pour the perlite into the shotgun fruiting chamber; it should be around 4 inches deep. Often people don’t put enough perlite into the SGFC resulting in low humidity levels, it is important to get around 4 inches of perlite in the box to avoid this.
Add water.
Pour water over the perlite until it is fully hydrated and wet to touch. I normally put a towel under the fruiting chamber while I do this to catch any excess.
Elevate The SGFC.
Finally elevate the shotgun fruiting chamber, at least 2 inches from the ground but more is probably better. This is an important step and shouldn't be skipped as fresh air is pulled through the bottom of the SGFC as part of its function, if the bottom isn't elevated this cannot happen.
For a proper explanation on why elevation is important and how a SGFC works read below.
How Does A Shotgun Fruiting Chamber Work?
A Shotgun fruiting chamber works in the following way:
Evaporation of Water from Perlite:
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- The perlite at the bottom of the SGFC is moistened with water. Perlite is highly porous, which means it can hold and gradually release moisture over time.
- As the water in the perlite evaporates, it increases the humidity within the chamber. This is essential because mushrooms require a high-humidity environment to develop properly.
Rising Humid Air:
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- The fruiting mushrooms placed in the chamber produce energy, which creates heat. Warm air tends to rise, and as it does, it carries the moisture from the evaporating water upwards through the chamber. This process helps to distribute humidity evenly throughout the chamber, surrounding the mushroom substrate with moist air.
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Fresh Air Exchange Through Ventilation Holes:
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- The SGFC has holes drilled all around it, including the lid and the base. These holes allow fresh air from outside the chamber to enter.
- As the moist, warm air rises and escapes through the upper holes, it creates a slight vacuum that draws in fresh, cooler air from the outside through the lower holes. This natural air exchange is crucial for reducing the buildup of carbon dioxide produced by the developing mushrooms and for supplying them with fresh oxygen.
- Fresh air exchange is not only vital for supplying oxygen but also for stimulating the mushrooms to fruit. In nature, the increase in fresh air, often signalled by a drop in carbon dioxide levels and slight changes in temperature or humidity, indicates to the mushroom mycelium that it's a suitable time to form fruiting bodies.
Does a SGFC Need Light?
No, most shotgun fruiting chambers do not require a light source, my advice is to place the tote in a room with a window giving it some indirect light however keep it well out of the way of any window which receives sun as this will create a greenhouse effect which raises the temperatures too high in the chamber.
What Are The Most Critical Factors To Monitor In A SGFC To Ensure Optimal Mushroom Growth, And Why?
The perlite inside the SGFC should remain moist at all times and do not let it dry out. The ambient temperature and humidity in the room will govern when it is necessary to mist the chamber, for example if the room is hot then the perlite will dry out faster, requiring more mists. Make sure to check regularly that the perlite is still moist to touch and keep it that way.
Fresh air exchange should be self regulating if humidity is correct, there should be no need to fan a SGFC.
What Are The Best Practices For Cleaning And Maintenance Of A SGFC To Prevent Contamination?
- Between grows, wipe down the SGFC with soapy water.
- Clean the perlite by submerging it in boiling water.
- Sanitize and reuse any tin foil which is under your cakes by wiping them with alcohol.
Can The Shotgun Fruiting Chambers (SGFC) Grow Be Scaled Up For Larger Production, And What Adjustments Would Be Needed For Larger Setups?
While Shotgun Fruiting Chambers (SGFC) are excellent for beginners in mushroom cultivation, they face scalability challenges for large-scale production. The primary issue is air exchange: stacking SGFCs often blocks crucial air holes, especially at the bottom, which are vital for mushroom growth.
Additionally, while SGFCs can be staggered at 90 degrees to allow some airflow, this arrangement is not space-efficient for mass cultivation.
Alternatives like monotubs and bucket teks, known for their stack-ability and space efficiency, are therefore preferred for larger-scale mushroom cultivation, offering a more practical solution for commercial operations.
Which Mushrooms Can Grow In A Shotgun Fruiting Chamber?
Shiitake.
Lions Mane.
Freckled Chestnut .
Pioppino.
King Oyster Mushrooms.
Which Mushrooms Do Not Grow Well In A Shotgun Fruiting Chamber?
The majority of Oyster mushrooms will not grow well in a shotgun fruiting chamber as they require a lot of fresh air exchange which the indoor environment of a SGFC does not provide.
What Are The Most Common Pests Encountered In A SGFC, And How Can They Be Prevented or Treated?
Fungus gnats can infiltrate a Shotgun Fruiting Chamber through its ventilation holes, posing a risk of infestation. They may lay eggs in the perlite or directly on the fruiting substrate. Initially, this may not cause significant issues, but without proper maintenance, such as regularly cleaning the perlite with boiling water, these pests can become a major problem.
Manage these pests in the following ways:
- Yellow Fly traps – these will help trap the flies.
- Treat house plant soil with Nematodes – Treat any house plants near your SGFC with nematodes which kill the Fungus Gnats larvae.
- Carnivorous Plants – consider buying and placing a carnivorous plant close to the SGFC, for example Sundew or ButterWort plants are particularly great at capturing fungus gnats (natures fly trap).