​What is a Shotgun Fruiting Chamber, and How Do I Build One?

Posted by J&K at APN on 2021 Mar 3rd

What is a Shotgun Fruiting Chamber, and How Do I Build One?

A shotgun fruiting chamber is essentially a container for maintaining high humidity around a mushroom fruiting block. Often called a sgfc, and named for the scattered ventilation holes reminiscent of a shotgun pattern. Shotgun Fruiting chambers are easy to build and need no special equipment. Once properly set-up, it will provide a nearly perfect flow of fresh air while maintaining the necessary humidity for mushroom fruiting.

Note: While a Shotgun Fruiting Chamber and a Monotub look alike, and can even be made from the same basic plastic tote, they serve very different cultivation methods. Check here for our in-depth look at building a monotub.

The basics

A shotgun fruiting chamber is a big clear tote with many holes drilled into the sides, and filled with a couple of inches of wet perlite in the bottom. The clear allows natural light in, holes provide fresh air exchange, while the wet perlite slowly releases moisture, maintaining humidity.


REQIRMENTS: Requires very basic tools and about an hour of time. 

RATED: Very easy/beginner level to build.

You will need

  • A clear tote with lid, roughly 50 quart size (locking lids work best)
  • 4 gal of Course Perlite (the larger sized the better)
  • Spray Bottle
  • Hygrometer (not needed, but helpful)
  • Power Drill
  • 1/4 inch to 1/2 inch drill bit
  • Measuring Tape
  • Sharpie Marker

Lets do this!

STEP 1: Make your drill marks

Using your measuring tape and sharpie make a dot every 2 - 3 inches on EVERY SURFACE of the tub. Yes, also the top AND BOTTOM of the tub. This allows airflow to come from the floor and up though the perlite into the chamber once it’s filled.

Step 2 Drill, and drill, and drill...

Use your power drill and slowly drill out each and every dot. (It’s boring, but it really only takes a few minutes)

STEP 3: Add glass, really!

Add 2-4 inches of perlite to the bottom of your newly created shotgun fruiting chamber. Soak the perlite with water until it begins to drain from the bottom holes. (It’s best to do this outside or in a bathtub to allow the excess water to drain away)

FYI: Perlite is a form of volcanic glass which expands rapidly when super-heated, creating large numbers of micro-pockets for water storage.

STEP 5: Enter the chamber

You’ve built it, now it’s time to put it to good use. Shotgun fruiting chambers can be used for fruiting any colonized substrate, mushroom grow kits, our BOOM Blocks, pf tek jars and nearly any type of mushroom spawn. It’s easy to judge the humidity level in a shotgun fruiting chamber. If the sides of the chamber have droplets of water forming it’s good.


Open and lightly fan the chamber at least twice per day. You are exchanging the stale air in the bottom of the tub for fresh air. After each fanning you will need to add some humidity back to the chamber by spraying the perlite surface.

Spray until the sides have a few drops sliding down into the perlite to replenish the water content. It’s best to NOT spray the mushroom substrate directly unless it appears dry.

TIP: An ultrasonic humidifier can exchange the air and keep the humidity correct at the same time. A small hose from the outlet to your chamber works great to maintain the environment.

Let there be (a little bit of) light!

Indirect natural sunlight is best for your mushrooms to grow. While mushrooms do not need light in the same way that plants do, they do need a little bit to grow really well. A few moments of light per day is plenty and to much light can be detrimental to the fruiting stage.

TIP: If you can see the mushroom chamber then there is enough light for the mushrooms to fruit. Most mushrooms will receive plenty of ight as you fan and mist them so extra light are not needed.

It’s easy. It’s cheap. It works.

You can build a fancy growing setup, but this works great! New growers and experienced cultivators alike employ these awesomely easy to make shotgun fruiting chambers for the best of reasons. Get growing!