Supported number of grow kits: 2–10,
depending on the size of plastic tub used.
Approximate cost: $50–150

Construction time: 30–60 minutes

This small automated fruiting environment can accommodate multiple fruiting kits, depending on the size of plastic tub used. Cost varies based on tool investment and adding optional materials.



Step 1: Prepare the tub

  • Drill four to ten 1/4” drainage holes in the bottom of the tub, or enough to ensure good drainage. Be sure to drill holes in the low areas as well.
  • Mark a line around the perimeter of the tub, 3 inches from the bottom. Drill 1/4” holes along this line every 2 inches. These are for venting out CO2 buildup. Optionally, cover these holes with micropore tape to keep insects out (not pictured).
  • Using the 1-1/4” hole saw, drill out a hole on one of the short sides of the tub, approximately 17 inches (on center) from the bottom of the tub. This is where the humidifier will be connected.
  • Using the 3” hole saw, drill out a hole on one of the long sides of the tub, near the top of the tub. This is where a computer fan will be connected to bring in fresh air.

Step 2: Connect the fan

  1. Tape the computer fan over the 3” hole, centering and squaring it where you would like it to be mounted. Using the 1/8” drill bit, drill a hole in the tub for each of the corners of the computer fan, using the fan’s holes as a guide.
  2. Cut a piece of the filter material to match the size of the computer fan (approximately 3” x 3”).
  3. Mount the fan to the tub with the 1 1/4” screws, sandwiching the filter material between the fan and tub. Be sure to mount the fan so that the air blows into the tub, not out of it.
  4. Plug the fan into one of the timers and set it to turn on for one minute every 15 minutes.

Step 3: Connect the humidifier

  1. Cut two pieces of PVC. The sizes of these will vary based on the size of your tub. You only need to them to be long enough to connect the humidifier as shown, ensuring the vertical piece is snug against the opening of the humidifier. Cut pieces longer than you think you will need them to be and trim them down as needed.
  2. Place a gasket on the 1” PVC threaded male connector and screw it through the 1-1/4” hole.
  3. Place a gasket on the connectors threads then screw on the 1” PVC threaded female connector, creating a “sandwich” of the gasket, tub wall, and gasket.
  4. Connect the 1” PVC threaded male connector to the PVC elbow horizontally, then the elbow to the humidifier vertically using the pieces cut in step 3.1. If cut properly, the PVC should be snug against the opening and not require any additional seals to send the fog to the tub.
  5. Plug the humidifier into the second timer and set it based on the the guidelines below.

Step 4: Prepare the bottom

  1. Line the bottom of the tub with one or two paint strainer bags.
  2. Cover these with 3 inches of perlite, or just enough to about 1/8 of an inch below the ventilation holes.

Optional: Add a reservoir

If you do not want to disassemble the setup to refill the humidifier, this additional step will make refilling significantly easier.

Additional materials:

Additional tools:

  • 1/8” drill bit
  • 1/2” drill bit
  • Needle file or long bolt
  1. Using the ½” drill bit, carefully drill a hole high up the side of the humidifier. Be sure to drill slowly, so as to avoid cracking the humidifier.
  2. Screw a 1/4 x 1/4 NPTF male adapter into the hole. If it does not fit, use a file or long screw to (carefully) file the edge and increase the hole diameter.
  3. Drill a 1/2” hole in the side of your reservoir near the bottom.
  4. Screw the second 1/4 x 1/4 NPTF male adapter into the reservoir, adding silicone as you do to ensure a water-tight seal.
  5. Allow the silicone to cure for 24 hours.
  6. Place the reservoir on the lid of the Mini Martha and connect it to the humidifier with a piece of tubing.
  7. Fill the reservoir as needed, keeping the lid on between uses.

Use and Maintenance

To use the Mini Martha, place the frame over a water collecting towel or tray (such as a large baking tray, shallow plastic tub, or small animal kennel tray) in an area with indirect sunlight or with a full spectrum light source (LED or fluorescent lights work well). Waterproof LED lights can also be placed on the inside of the lid of the tub, creating a more self-contained system. Finally, place your kit(s) in the tub after they have been prepared for fruiting (as detailed in the instructions provided with each kit).

Turn on the humidifier until a light mist develops on the walls of the tub alongside light streaking down its walls. As the fan turns on every 15 minutes (so as to bring in the fresh oxygen that the mushrooms need), the humidity level will drop. Watch your setup and adjust the humidifer’s timer to turn on after the fan turns off, and to then run as long as is needed to bring the humidity level back up. Within a day or two you should be able to determine the best setting for the humidifier’s timer and thereafter only need to adjust its setting as the seasons change and ambient humidity and temperature levels affect the fruiting environment.