Supported number of grow kits: 1–32
Construction time: 90–120 minutes
Approximate cost: $100–250

Mushroom development requires a dedicated fruiting environment that maintains specific levels of light, warmth, humidity, and carbon dioxide. While the MYCOLOGOS Mini Martha addresses these constraints when fruiting 1–3 of our grow kits, fruiting more kits requires a larger space. A popular approach in this regard is modifying an indoor greenhouse marketed for plant growing to provide the needs for maturing mushrooms. These systems are often referred to as “Marthas" by mushroom growers in reference to indoor greenhouses once sold under Martha Stewart’s line of home goods.

One approach to a Martha design is to place an ultrasonic humidifier on the bottom shelf of the greenhouse and set it on a minute timer to maintain 85-95% relative humidity. Fresh air is thereafter provided by partially unzipping the front of the greenhouse, or by cutting holes throughout the greenhouse’s slip. Light is provided by indirect sunlight or by a full spectrum or 6500K LED set to illuminate for 12–18 hours per day. Example Martha design styles are here and here.

While these systems work great for many growers, described below is the MYCOLOGOS Mother Martha (MMM): an upgraded version of these popular fruiting spaces that incorporates full automation, full light coverage, even fog dispersal, and water collection features – all inside of a small footprint. Though the cost of building the MMM is higher than for the designs linked above, we feel the investment is well worth it for people planning to grow at this scale for many years.


  • Scissors
  • Box cutter / knife
  • Measuring tape
  • Electric drill driver
  • 1/4" and 1/2" drill bits
  • Hole saw set
  • Something to cut PVC, such as a hand saw, miter saw, sharp knife, or PVC cutter. Most hardware stores will also cut PVC for free.


Step 1: Prepare the Materials

  • Determine where you will place the MMM. Ideal locations are near a water and electrical source, and where temperatures are cool and easily controlled. You will also need a shelf above the MMM to hold the humidifier (our shelf is 65.25 inches off of the ground).
  • Drill a 2.5" hole in the center of one of the tote’s long sides, centering the hole 5.25 inches from the bottom of the tote. Run a bead of silicone around the outside and inside of this hole. Place the 2" PVC threaded male adapter through the hole, sandwiching a flush valve shank washer between it and the outside of the tote. Place another flush valve shank washer on the threads of the male adapter (inside the tote) and then screw on the 2" PVC threaded female adapter, creating a snug fit. Run more silicone around each flush valve shank washer, ensuring that both sides of the seal is going to be watertight.

A bead of silicone is run around both sides of the hole, and the male adapter inserted. The shank washer is positioned so that its angled side points toward the hole.

More silicone is applied to both sides of the seal, making it watertight.

  • Run a bead of silicone around the lip of the tote's opening, then allow the tote to sit for 24 hours while the silicone cures.
  • Cut the PVC to the following lengths:
    • (1) 3" segments of 2" PVC
    • (2) 44" segments of 1" PVC
    • (2) 10.75" segments of 1" PVC
    • (2) 1.75" segments of 1" PVC
    • (2) Segments of 1" PVC, the length of which will be based on the height determined in step 4.3
  • Drill 1/4" holes in a single, straight line down each of the two 44" PVC segments. Space the first hole 3 inches from one end of the segment, then space the rest of the holes 6 inches apart.
  • Cut the coroplast into the following pieces:
    • (2) 19” x 54”
    • (1) 26” x 54”
  • Cut the waterproof tape into the following lengths:
    • (2) 19"
    • (1) 26"
  • Cut these tape strips in half lengthwise, then tape off the top and bottom of the coroplast pieces, sealing off the inner channels of the coroplast (so as to reduce the risk of contaminant growth in these channels).

Step 2: Prepare the Greenhouse

  • Assemble the greenhouse, then zip tie its shelves to its cross bars.
  • Starting in a back top corner of the shelves, run an LED strip down each vertical post of the frame, around the bottom, then up the other side, all while using zip ties to secure the strip as you go. Angle the strip so that the lights face the center of the greenhouse. Make sure you start the strip so that its plug is in an upper corner of the greenhouse.

The LED strip points toward the center of the MMM and is secured by zip ties to the frame of the greenhouse.

  • Cut a 1/2" slit in a back top corner of the greenhouse's slip to run the plug for the LED strip out of. Plug in the light to make sure the LED strip is lighting the shelves evenly. Adjust the light strip’s position as needed.

The plug of the LED lights runs out of the back of the greenhouse via a small slit cut in the slip.


  • Cut a 1" hole in the top center of each of the short sides of the slip and use a 1" threaded male PVC connector, 1" threaded female PVC connector, and a rubber gasket to create a PVC channel that is watertight.

Male and female adapters, along with rubber gaskets, sandwich the greenhouse's slip, making an airtight seal.

  • Attach one of the drilled 44" PVC segments to the inside left connector, facing its holes toward the center of the greenhouse. Attach a 1" PVC valve at this segment’s base, then use a 1.75" segment to connect an elbow connector to the valve, facing the elbow connector toward the center of the greenhouse. Use zip ties to secure this vertical PVC assembly to the shelving frame.

Holes drilled in the 44" segments of PVC point toward the center of the MMM.

An optional drain valve maintains pressure in the system, while helping collect pooled water as needed.

  • Install the other 44" segment, elbow, and valve on the right side of the greenhouse.
  • Attach the coroplast pieces to the sides and backs of the shelving unit by cutting small slits along the edge of the coroplast and then running zip ties through the holes. Adding these walls is optional, but will enhance light distribution, while providing some insulation for the fruiting space.

The coroplast is attached to the greenhouse frame via zip ties that are run through small slits cut in the coroplast.

  • Place the greenhouse on the kennel pan or water heater tray, ensuring the coroplast walls are tucked in the pan. Then fold the bottom of the plastic slip’s sides and back under the shelving’s feet, ensuring that water from the humidifier will collect in the tray/pan and won’t spill on the ground.

A finished inner wall of the MMM. A perforated PVC pipe distributes fresh, humid air along the shelves, and a drain valve helps control water collection at the base of the pipe. Behind the pipe, a wall of corrugated plastic helps distribute light, while also providing insulation to the system.

Step 3: Finish the Humidifier

This step creates an auto-refilling humidification system that provides fresh, filtered, and humid air to the greenhouse at regular intervals. Water is provided by a float valve inside of a plastic tote, which is connected by 1/4" vinyl tubing to a pressurized water source, such as a sink or hose.

In our setup, the pressurized water source was a shut-off valve beneath a utility sink, to which we connected a 2-way splitter that ran one line back up the sink’s faucet, and another to the tote. Connecting to a hose would also work, though for any system you will need to determine the appropriate connectors for creating a watertight supply line.

  • Drill two 1/2" holes on the other long sides of the tote, centering both holes 4.5 inches from the bottom of the tote and 3.5 inches in from either side.

  • Push the float valve’s metal rod all the way into the plastic float, minimizing the float’s overall length. Run the threaded end of the float through the tote’s right hole, wrap the threads in teflon (plumber's) tape, and attach a 5" segment of vinyl tubing using a 1/4" compression insert and compression sleeve.
  • Mount the tubing to the wall using the tubing clips.


The rod is pushed all the way into the float. On the right are the connectors used to attach the float to the push-fit valve.

  • Connect the push-fit valve to the tubing, then connect the valve to the water source.


The tubing from the float valve is connected to a push-fit shut off valve, which then connects to the water source.

  • Run the ultrasonic humidification float’s power line out of the tote's left hole until only around 4 inches of power cord is left in the tote. If the float’s cord does not have an integrated rubber grommet to plug the hole, wrap silicone tape around the cord to create a watertight gasket.
  • Attach weather stripping around the perimeter for the tote’s lids, outside of the bead of silicone.


The finished humidifier bottom. Note the silicone tape wrapped around the humidification float's cord (left), creating a seal. Also note the bead of silicone and weather stripping around the lip of the tote.

  • Drill a 4" hole in the center of the tote’s lid. Insert the 4" starting collar in the hole and flip the collars tabs on the lid’s underside, securing the collar in place. Cover the tabs in waterproof tape, then tape the other side of the collar to the tote’s lid.

After folding up the tabs on the collar, waterproof tape (not pictured) is applied to secure the seal.

  • Attach the 4-inch inline fan to the starting collar and secure it with a ducting clamp. Make sure the fan is oriented so that air goes into the totes, not out of it. Attach the HEPA filter to the top of the fan and secure it with a second ducting clamp.

The finished humidifier lid.

  • Turn on your water supply and check for any leaks. If the float valve leaks from the back, the compression collar may have been installed improperly or the water pressure may be too high. Closing the supply line valve slightly will reduce pressure to the float, potentially halting leaks.
  • Plug in the fan and humidifier and ensure that both work properly, that there are no leaks in the system, and that mist is only coming out of the 2" PVC at the front of the tote.

Step 4: Put it All Together

  • Place the MMM into position and center the humidifer tote above it on a shelf.
  • Use the 3" segment of 2" PVC to attach the 2" PVC T-connector to the tote's 2" PVC threaded male adapter. Attach a 2" to 1" PVC reducer to both sides of the 2" PVC T-connector.

The finished humidifer. A HEPA filter connects to an inline fan, which blows filtered air into the tote. Fog exits the 2" PVC, builds a plenum in the 2" to 1" reducer, and is distributed to both sides of the greenhouse.

  • Attach a 10.75" segment of 1" PVC to the left side of the 2" T-connector, then attach a 1" elbow connector to the end of the segment. Attach a segment of 1" PVC to connect this elbow vertically to the 1" PVC adapter on the left side of the greenhouse. As noted in step 1, the length of this segment will vary based on the height of your exact setup. Our segments are 12 inches long.
  • Repeat the above step for the right side of the greenhouse.
  • Once you are certain that all of the PVC pieces fit properly, apply PVC cement as desired to create an air-tight system.
  • Plug the LED lights into the 24-hour timer, setting it to run for 12–18 hours per day.
  • Plug the fan and humidifier into the 3-plug adapter, then plug this adapter into a minute timer. Set the timer following the maintenance information below.
  • Zip the greenhouse door closed and wait for a visible amount of humidity to build inside.

At top, a minute timer controls both the fan and humidification float. Below, the lights are set to a 12/12 cycle.

The MYCOLOGOS Mother Martha.

Use and Maintenance

As you start to fruit mushrooms in the MMM, you will need to adjust the timer settings on the humidifier to ensure that the CO2 and relative humidity levels are just right. A good hygrometer will help with checking the humidity level, while observing the mushrooms themselves is the best way to know if the air is being cycled often enough. If your mushrooms develop long stalks or get moldy quickly, it is likely that the air is too stagnant in the system and needs to be cycled more frequently. Likewise, if the mushrooms look or feel dry and do not fully develop, this is a sign that the air is too dry.

Over time, water will collect in the bottom of the vertical poles inside the greenhouse. Open the valves at the bottom of these poles to collect this water as needed. Likewise, cleaning the water collection pan and the greenhouse’s walls will be occasionally required to mitigate mildew, mold, and bacterial growth.

Otherwise, just be sure to use your new automated space! Setting up a well-functioning fruiting space is one of the first logistical hurdles that growers encounter as they start to scale up their practice. Now that you've come this far, enjoy the fruitbodies of your labors and grow, grow, GROW!