February 24, 2012

Build a Grow Chamber

A terrarium or fruiting chamber is an artificial habitat that mimics your magic mushrooms natural ecosystem. It is used to ‘fruit’ your substrate cakes and yield you mounds of fresh, highly potent fungi.

NOTICE: This section does not cover making substrate cakes which requires separate supplies and is covered HERE.


The instructions detailed here will build the cheapest and easiest terrarium known as a ‘Shotgun Terrarium’ grow chamber.

Don’t be fooled by its utter simplicity. It was designed by a mycologist with over 30 years of mushroom cultivation experience. The terrarium even factors in physics, air density and altitude differentials.


Shotgun Fruiting Chamber – Principles of Operation

This terrarium is about as simple and easy as they come and can be built in less than half an hour. The shotgun fruiting chamber (SGFC) as it is known naturally ventilates and humidifies without the need for fans or any other mechanical devices.

The secret is drilling 1/4″ holes over the entire six sides the terrarium in a 2″ x  2″ grid pattern. The holes allow natural currents of air to travel from areas of high pressure to areas of low pressure which keeps fresh air circulating throughout the grow chamber.

In a nut shell, a pressure differential is created by placing  a 4″ to 7″ layer of saturated well drained perlite at the bottom of the terrarium.

The slightly warmer air above the perlite results in a pressure gradient that causes air to flow from the bottom of the terrarium up through the moist perlite, drawing in moisture and humidifying the terrarium while exhausting excess CO2 out of the top. Because a shotgun terrarium has holes on the bottom it must be raised off the ground to work properly.

The only real drawback if you even want to call it that is the need to mist and fan your terrarium at least once every 12 hours (4-6 times a day is optimal but not necessary). While many people have attempted to modify the original shotgun terrarium design with fans, humidifiers and or foggers. Nothing has worked better than an otherwise properly constructed shotgun fruiting chamber.



  • Sterlite Clear Plastic tote
  • perlite
  • Handheld Fan (Or Xbox Game Case)
  • hand mister
  • Drill
  • 2″ Wood Blocks
  • Humidor Hydrometer


Construction Instructions


1) Measure out and mark a 2″x 2″ pattern of dots evenly spaced over an entire sheet of graphed or lined paper.

2) Hole punch or poke out the grid marks to create a stencil.



3) Overlay the stencil onto your clear plastic tote/bin and mark out a 2″ x 2″ grid pattern on all six sides.

4) Use a 1/4″ (6mm) drill bit and make your shotgun chamber holes.



Clean the new fruiting chamber with rubbing alcohol and place on wood blocks.

Sterilize and bake your perlite at 350 for 30 minutes.When cooled rinse in a strainer under the faucet.

When the perlite has drained well dump it into the bottom of your terrarium to build a 4″ layer of damp but not wet perlite.





Using your Shotgun Fruiting Chamber

Your new fruiting chamber is now ready to turn your mycelium cakes into potent magic mushrooms. Make sure the ambient humidity in your house is 30% or above. If you live in a climate where the humidity is too low make sure to get a cool mist humidifier for your home first.

Keep the fruiting chamber on a shelf or table but never on the ground as 90% of all airborne contaminants in a room are located near the floor. After you place your cakes inside the chamber you will want to take the lid off at least once ever 12 hours to fan and mist the perlite with water.

Keep your terrarium’s temperature between 70F – 80F. Try not to let the temperature fluctuate wildly as this will stress your growing magic mushrooms. It is best to keep the temperature reasonably constant in the low to mid 70s.

Magic mushrooms all require light to produce abundant, normal sized fruits. If for privacy reasons you cannot place your fruiting chamber near a window for ambient light use a 15 watt CFL (day light bulb 5,000 K to 7,000 Kelvin) placed on top of the terrarium.


Next Section | Fruiting


Elite Growers Guide