Updated: Jul 21
How to easily make your own Affordable Shotgun Fruiting Chamber
Mushrooms grow optimally in an environment with sustained humidity and some fresh air-flow. For a minor investment of time and funds building your chamber, you can expect to increase your mushroom-yield by up to 50% or more.
Slow-growing mushrooms, like our native 'Lions Mane' (Hericium Novae-Zelandiae), can take 3-5 weeks to grow to maturity, so moisture and humidity control are vital to get good results.
Simple fruiting chambers are very affordable to make, usually substantially increasing yield and quality from >> mushroom grow kits, and allow you to grow certain species you otherwise could not.
Rough estimated build cost:
Sistema Container: $30NZD
Time to make one: 15-20 minutes
What Is A Shot Gun Fruiting Chamber?
Shot gun fruiting chambers are essentially just a large 50-90+ L clear plastic box with many small holes drilled in them to allow for some fresh air exchange. Wet >> perlite is put in the bottom of the tote to help increase humidity.
It's best to use a clear plastic tote to allow natural light into the box for your mushrooms. CO2 produced by the mushrooms is heavy and will flow out of the lower holes drawing in more fresh air from the top holes in the box.
How to Build a Basic Shot Gun Fruiting Chamber (SGFC)
Drill bits 6-8mm
90L Sistema Tote
Measure and mark out where to drill the holes on the tote -- the holes do not have to be perfectly uniform, you just want them spaced out reasonably evenly around the whole box for even airflow. Holes should be drilled with a 6-8mm wide drill-bit, roughly 50mm apart. Start with the first line of holes about 90-100mm up from the base of the tote; this allows for a good layer of wet >> perlite to sit in the bottom -- with no risk of water leakage. Each row of horizontal holes should be at about 90mm above the line of the holes below.
Begin drilling all the holes including holes in the lid. When drilling holes into the plastic be careful not to press too hard with the drill-bit to avoid cracking the plastic. Run the drill on high-speed and drill slowly with minimal pressure applied, almost letting the drill bit melt into the plastic. Sistema plastic containers are the best plastic to drill and the least likely to crack. Cheaper brands of totes tend to crack very easily and can become weak after all holes are drilled. Once you have finished drilling clean up all excess plastic, scraping dangling pieces off the holes.
Add the dry perlite to the tote in an open air environment, taking care not to breath in the dust from the perlite. Begin adding water to the perlite and mixing it around until the perlite is at field capacity. ('Field capacity' refers to when the substrate cannot hold any more water). Allow the perlite to drain for a few minutes and then spread evenly in the bottom of the tote.
Your tote is now ready to use. Place your mushroom grow kit into the tote -- the water in the perlite will help keep the humidity high. For extra humidity during dry months it can be good to spray the sides of the tote once or twice a day with fine water-mist. You should also fan your tote at the same time - once or twice a day again. To do this simply take the lid and use it as a fan to blow out the air inside the tote -- replacing it with fresh air. This process helps keep the air extra fresh and co2 levels at a minimum (which is most important for oyster mushrooms). The perlite should be replaced as it gets dirty. If you see any mould growth on the surface of the perlite it is time to replace it. Perlite can be added to your garden once dirty.
Optional Humidifier Upgrade
By adding on a simple automatic humidifier we can maintain perfect humidity inside the fruiting chamber and accurately adjust humidity levels for different types of mushrooms. This will help you get higher yield, more consistent, high-quality mushrooms year round.
With the fan supplying constant fresh-air you will not need to manually take the lid off during the day to fan the chamber or spray water on the sides of the tote. Perlite is not 100% necessary with the humidifier so long-term running costs can be a lot less, as you will not need to purchase replacement perlite.
From here I will explain how to upgrade your SGFC tote to have a mini-humidifier attached to it. This can be run on a timer or with an Ink Bird humidity controller. Links to where you can buy the products referred to are at the bottom of this blog post.
Tools and Items Needed:
Drill and drill bits
Hole Saw attachments (20mm, 32-40mm, 54-56mm).
88°-90° PVC Bend 32mm - available at Mitre10 or Bunnings in NZ
Male Thread Adaptor PVC 32mm - available at Mitre10 or Bunnings in NZ
Female Thread Adaptor PVC 32mm - available at Mitre10 or Bunnings in NZ
Length of 32mm PVC Pipe and saw to cut it. - available at Mitre10 or Bunnings in NZ
1x Pond Fogger/Mist Maker
10L Sistema Container
Hot glue gun or double-sided tape.
Humidifier Estimated Build Costs:
PVC Fittings: $30-50NZD
10L Sistema Container: $14NZD
USB Fan: $5-10NZD
Mist Maker: $15-35NZD
Humidity Controller: $50-60NZD
Time to Build One: 30-60 mins
On the 10L container measure out roughly the middle of the lid and mark with a dot. This will be where you drill the hole for the male and female adaptors to screw together into the lid. Drill carefully and slowly. Once drilled clean up any rough edges and screw the two adaptors together. Now measure the 32mm pipe with the right angle on top of it to go into the two adaptors and end up just below the top of the fruiting chamber.
Measure the diameter of your fan-blade and cut/ drill a hole in one of the corners of the lid for the fan to sit on top of -- be sure to allow enough plastic for the fan to be secured to the lid. Check the side of the fan for air-flow direction before attaching it -- you want the air blowing into the unit. ;)
Now drill a hole in the side or in the lid for the cord of the pond fogger to go through. The pond fogger will come with a rubber bung on the cord. Measure the bung, then drill a hole a few mm smaller than the widest point of the bung to get a tight-sealed fit.
Sit your newly-made mist maker beside your tote and eye where the hole needs to go for the 32mm PVC pipe to feed into the tote (roughly 50mm down from the top of the tote), mark this and drill the hole in the side of the tote with a hole saw. Next measure and cut a piece of 32mm PVC pipe to go about 1/3 of the way into the tote. This is where the humid mist and fresh air will be pushed into your mushroom fruiting chamber.
Running the humidifier:
Fill the reservoir with water so it is about 5-6cm above the top of the fogger head, mark this level for future filling reference. Plug the fan in so it runs 24/7 and plug the pond fogger into the Ink Bird humidity controller. Set the humidity to 90% with the differentials about 2 points above and below the 90% set point -- this will make the humidity in the tote fluctuate between 88-92% humidity. Make sure the humidity sensor is inside the tote. If you are finding the tote is very wet or too dry adjust the set humidity by a couple % at a time and see how it looks 12-24 hours later. The water in the reservoir will need to be topped up every few days, sometimes daily depending on the ambient humidity -- clean tap water is fine to use. Reservoir should be cleaned out and washed fortnightly. Painting the reservoir black will help stop algae etc growing as fast.
Make sure to not place the fogger head directly below the fan. When the ultrasonic head is running it will send water droplets into the air above it -- which we don't want hitting the electric fan.
The humidifier can be attached to the Shot Gun Fruiting chamber design laid out above or a more simple fruiting chamber. A simplified chamber can be made with fewer, larger, 20-25mm holes. Less holes are optional as the fan will supply constant fresh air pushing out the CO2 produced by the mushrooms.
A simple 90L tote with a single line of slightly larger holes (20-25mm diameter) around the base can be made to use with this unit. Simply measure out 3 holes on the long side and 2 holes on the short ends 80-100mm up from the bottom of the tote, mark and drill. Fill the bottom of the tote with wet perlite as usual.
Totes should be cleaned between grows to help reduce contamination growing on new kits that are ready to fruit. These work very well for >> Shiitake Grow Kits, our >> 5 Step Oyster Mushroom Grow Kits, Native Lions Mane Grow Kits (Hericium Novae Zelandiae), >> NZ Native Oyster Mushroom Grow Kit (Pleurotus Parsonsiae). Pretty much all mushroom growing kits will grow and produce much better in a humidity-controlled environment with good air flow.
Ink Bird Humidity Controller: