How To Build A Shotgun Fruiting Chamber (SGFC)

A Complete Guide With Step-By-Step Images

Growing mushrooms at home is a fun and rewarding project that anyone can do with a basic understanding of how mushrooms grow and what their needs are. What can make mushroom cultivation a little bit tricky is the fact that fungi require a particular environment to thrive. They prefer a humidity that is higher than the average household level. Gourmet edible varieties like Oyster, Shiitake, and Lion’s Mane also need adequate natural light and plenty of airflow. 

The most critical part of growing mushrooms is achieving the right balance between humidity and fresh air exchange, because although fungi like a high-humidity environment, they can also essentially “drown” if there’s too much moisture. Mushroom cells exchange gases directly with the atmosphere, so if the fruiting body is saturated with water, oxygen can’t be exchanged. This can cause anaerobic bacteria to thrive, choking out the mushroom and leading to spoilage.

We generally suggest to our customers to set up a simple humidity tent for their mushroom grow kits because it’s the easiest solution and can be put together with ingredients most people have on hand. However, if you’re getting more into growing mushrooms, you’ll find even greater success with a shotgun fruiting chamber. It’s not very difficult to set up, and it creates a superior environment for mushroom growth! There are lots of variations and designs so get creative but keep key growing conditions in mind. 

What’s a shotgun fruiting chamber?

Like a little mushroom greenhouse, a shotgun fruiting chamber is an easy setup that creates the ideal environment to grow fungi in. Essentially, it’s a clear bin filled with air holes with a layer of damp perlite on the bottom. With just a few basic ingredients and tools, this type of DIY mushroom grow chamber takes all of a mushroom’s favorite things into consideration - humidity, air exchange, and light. There are three significant pieces at play here:

1. The holes are absolutely necessary for airflow and gas exchange. As mushrooms grow, they produce CO2. Carbon dioxide is heavier than air and needs to be able to escape the fruiting chamber so fresh oxygen can get in (mushrooms need to breathe just as we humans do!).
2. The tote should be clear so your mushrooms get adequate natural light. A clear lid is also preferred, but an opaque one should be fine as long as the mushrooms are getting a decent amount of light into their chamber. 
3. The perlite is what’s going to help create a humid environment. Often used in gardening and farming as a soil amendment, perlite is a material made from volcanic rock. The coarse bits of soft rock hold water in all their little nooks and crannies. Over time, this water will slowly evaporate, creating humidity. 

Setting up a mushroom fruiting chamber

You’ll need:

• A clear tote (about 70 qt for 2 kits, or big enough to grow your mushroom kit with some extra space)
• A drill with ¼” bit
• Coarse perlite (1 - 2 gallons)
• Spray bottle
• Measuring tape and/or ruler
• Sharpie 
• Small wood block (Approx. 6” x 3” Inches, optional, but recommended) 

Step 1: Mark For Holes

Mark your tote all over for where you’ll be drilling holes. With your measuring tape and sharpie, mark for holes on every side of your container, including the lid. For the best results, create a grid of holes spaced two inches apart throughout the bin. Start your grid 4 inches from the bottom of the tub so that you’re above the perlite line. 

Step 2: Drill The Holes

Drill all the holes using a ¼” bit. Go slowly and use a light hand so you don’t crack the tote accidentally. When drilling, brace the tub wall with the wooden block to prevent the bin from flexing and cracking. It will also protect your hand! Brush away any little plastic shards left behind from the drilling process, then wash and dry the bin. 

Step 3: Add & Moisten The Perlite

Fill the tote with enough coarse perlite so that there’s 2-3 inches of it at the bottom. Pour distilled water over the perlite, mixing it with your hand or a wooden spoon to distribute it evenly. You want just enough water to moisten the perlite, but you don’t need to soak it. You don’t want standing water in the bin! 

Bonus points: To perfect your DIY mushroom setup, use a hygrometer to keep track of humidity levels. Using this tool will help you learn how often to spray your chamber and what works best for each type of mushroom at different stages of the growth cycle. The ideal humidity level is 75-90%, so make sure to find a hygrometer that can measure relative humidity that high.

Your mushroom grow chamber is now ready! It’s time to place your growing kit in the bin and find it a nice place to live.

Keeping your mushrooms happy 

When deciding where to house your mushroom growing setup, consider light, air flow, and temperature. Keep it in indirect sunlight - direct light from the sun can cause your chamber to overheat. The ideal temperature is between 55-75 degrees Fahrenheit, depending on the mushroom variety. Shiitake can stand to be a little on the cooler side, while Oyster mushrooms and Lion’s Mane prefer to be at least in the sixties. 

Keep your fruiting chamber somewhere where it can get good air exchange. A stagnant corner can be equally as harmful as an overly drafty area. You don’t need air blowing directly on it as that could dry out fruiting blocks - you just need it to be able to breathe. 

To take care of mushrooms in a shotgun fruiting chamber, remove the lid from the tote and use it to fan fresh air into the bin at least twice a day. Spray the perlite and the inner walls of the chamber using a spray bottle filled with distilled water once a week. The perlite will create enough humidity that you shouldn’t need to spray it more often than that. Avoid actually spraying the mushrooms as much as possible, as this can lead to mold growth.

Left: Mushroom growing kits in the fruiting chamber. Right: The perlite maintains a high level of humidity without needing to mist your kits every day!

Check in often to assess the health of your mushrooms and adjust any inputs as necessary. If the fruiting bodies are starting to wither or crack, they need a higher level of humidity. Mist the container and perlite more frequently. If your kit isn’t producing mushrooms, you may have too much moisture or not enough airflow. You can experiment with adding more air holes to your container or leaving the lid off for periods of time throughout the day. For specific needs based on mushroom variety, see our detailed article about growing mushrooms at home.

The more you grow your own mushrooms, the more you’ll understand and begin to master the process. We hope you find it as fascinating and rewarding as we do!