Build an Automated Mushroom Fruiting Chamber

 · 8 mins read

I’ve been getting into mushroom cultivation lately, initially as a hobby but with potential to start a business. I like the idea of being a mushroom cultivator, but like most people I don’t have any formal education on the topic. I don’t even remember mycology being a topic in gradeschool. So to get a feel for it, I decided to try my hand at growing something.

Right off the bat I bought an Oyster mushroom spawn kit from Home Depot for $20, followed the instructions (incorrectly), and managed to grow some blue-green mold… but no mushrooms. Time to double down!

Turns out there is more than one way to fruit a block. I’ve seen amazing variety in grow tent design across Shroomery and the wide web, with some being better than others. However, I couldn’t quite find any guides that met my particular style of over-doing things.

Thus, after many hours of YouTube and scrolling through forums, I identified a few trends: There seems to be a lot of love out there for the Martha style tent from small growers. I also noticed strong support for House of Hydro humidity systems from commercial growers. So that is what I built. Let’s dive in!


This is not a cheap build. It’s gonna cost ~$400 depending on where you source your parts. The bulk of the cost coming from the humidifer components. This build is designed for use with a few assumptions:

  • The ambient humidity is lower then 70%
  • The ambient temperature is stable between 55F and 65F degrees

This is an indoor grow build. If your location requires controlled heating/cooling or de-humidification, this may not be the build for you.


Picking a location to place your tent is important. There are a few factors to consider:

  • Temperature
    Choose a location that has relatively stable temperature throughout the day. Big sudden swings in temperature are bad. I chose a spare bedroom that doesn’t get a lot of foot traffic, so the door stays shut.

  • Humidity
    Maintaining humidity is a big factor in the Martha style tent. Similar to temperature, pick a location that has relatively stable ambient humidity.

  • Fresh Air Exchange (FAE) The fresh air coming into the tent needs to be clean/filtered. Since my tent is in a closed room, I simply use the ambient air in the room, provided by the central HVAC system, which is HEPA filtered.

  • Exhaust
    Some mushroom spores can cause development of allergic type reactions, so it’s important to ventilate to the outside, and not into your house. Pick a room that has a window, or where you are comfortable cutting a hole in the wall for exhaust ventilation.

  • Noise
    The system makes a minor level of noise as it operates. Mostly just the sounds of moving air and bubbling water. Use caution if sharing a wall with a bedroom or office.

  • Light
    Mushrooms enjoy a regular day-night cycle for fruiting. Place the tent in an area that allows for 12 hours cycles of light/dark.

  • Water (optional) If you have the option, consider placing the tent near a water line, or running a dedicated line to your tent location. This allows for the humidifier to be adapted with an auto-fill valve, for a set and forget type setup. I did not do this initially, but will be upgrading later.

Build Instructions

To build this Martha, I used parts from Amazon, Home Depot, and the House of Hydro. Some things, like fans, can be substituted with similar parts. It doesn’t have to be exact.


My core tent consists of the Martha tent itself, a plastic base, and a shallow perlite tray. The plastic base is for catching any condensation or dripping water, and the smaller perlite tray is for humidity control.

Tent: Gardman R687 4-Tier Mini Greenhouse, 27” Long x 18” Wide x 63” High

Base tray: MidWest Homes for Pets Dog Crate Replacement Pans, 30-Inch
Perlite tray: MidWest Homes for Pets Dog Crate Replacement Pans, 18-Inch

2 x Air diffusing ventilation port, 4-inch

Start off by assembling the tent in your desired location. Nest the perlite tray in the base tray, and slip them under the assembled greenhouse tent.

At the top, left/right side of the marth tent, just below the roof, trace a 4-inch circle using one of the ventilation ports and cut out a hole for mist intake. Cut out a similar hole at the bottom of the tent for exhaust output.

Attach the diffusing ventilation ports to the two openings. Ensure that the diffusers are open and allowing air to flow. You can adjust these to tweak how air flows through the tent.

Fill the smaller tray with damp perlite to help regulate the humidity level.


Mushrooms recognize a day/night cycle to indicate fruiting conditions. This can be simulated with a T5 florescent lamp and a timed power strip. We’ll need rope to suspend the light as well.

Via whatever hardware, hang the T5 light outside and above the tent using the adjustable ropes.

Plug the light into the timed power strip on the timed side.


Perhaps the most important and costly aspect of this build is the humidity system. Hands down The House of Hydro has the best gear for building a custom humidifier. I picked up the mist maker, humidistat, and humidity controller as well. Most everything else can be picked up at a hardware store (or Amazon).

Using a rotary tool, knife, or other sharp object, cut two 4-inch hole in opposing corners; One is for air intake, while the other is for mist output.

Attach the muffin fan to the top of one of the openings using nuts/bolts, making sure that the air is blowing into the resevoir (not out).

Connect the fan components together:
Muffin fan -> Fan speed controller -> Cable extension splitter

Using clear silicone, affix the PVC flang atop the other opening in the resevoir lid. I used bolts and wingnuts as well for an extra sturdy fixture.

Grab the ultrasonic mist maker head w/ float ring and place it inside the resevoir, then drill a hole near the output port large enough to run the mist maker cable up through. Seal up the hole with clear silicone to prevent mist leakage.

Attach the mist maker components together:
Mist maker -> Transformer -> Mist output controller -> Cable extension splitter

Attach the humidistat components together:
Cable extension splitter -> Humidistat -> Power strip, on the switched side

Once everything is connected up, place the humidifier unit next to the tent and connect the PVC pipe to the mist output flange. Then run ducting from the PVC opening to the upper tent ventilation port.


For heating, I have a simple seedling heating mat and thermostat controller.

Place the heating mat under the perlite tray at the bottom of the tent. Run the cable out of the tent and to the thermostat controller, then to the power strip on the switched side.


To promote fresh air exchange (FAE), I added an inline fan to my exhaust tubing. This is used to help dial in the temperature/humidity/FAE balance.

Use ventilation ducting to connect the output port of the tent to the inline fan, and then to your air output location. I built a wooden shim for the window, with a 4-inch hole and flange.

Control station

This setup involves quite a few wires and devices to keep track of. To organize the madness, and get the devices off the ground, I zip-tied it all to a plastic crate. The devices are attached atop, while the cords are fed through the holes and bound neatly within. Get creative, find what works for you and your space.