Mushroom Automation

A one-page guide

Keep the tent where the mushrooms want it, without standing over it.

Gourmet mushrooms fruit well inside a narrow band of humidity, fresh air, light and temperature. This page explains how a humidifier, a controller, a timer and a couple of fans hold that band for you, from a two-part setup to a sensor build that logs to a dashboard.

The chamber

One Martha-style tent, twelve parts, one job

A Martha tent is a wire shelving rack wrapped in a clear cover. Hover or tap any part to see what it does and what it connects to, then play a simulated day to watch the light, fan and mist run on their schedules.

Cutaway diagram of an automated Martha-style fruiting chamber Front section through a wire shelving rack of mushroom blocks inside a clear tent. An LED light hangs under the top of the rack, an exhaust fan sits high on the right wall with a duct to the outside, and a filtered intake vent sits low on the left. Outside the tent on the left, a humidifier feeds mist in through a hose above the top shelf and is switched by a humidity controller that reads a probe hanging mid-tent. On the right, a timer strip runs the light and the fan. Everything plugs into GFCI outlets. A drip tray sits under the lowest shelf. Fig. 1 Automated fruiting chamber, front section. Not to scale. 1Tent shell 3Grow light 2Blocks 4Exhaust fan 5Intake vent 7Probe 9CO2 sensor RH 88 % SET 85 / 90 8Controller 6Humidifier 06:00 10Timer 11GFCI outlets 11 12Drip tray
Front section through a Martha-style tent. Hover or tap a numbered part, or use the list. The drawing is a sketch of how the parts relate, not a wiring plan.
Readouts simulated
Time06:00
Humidity88.0 %
Temperature20.4 °C
CO2700 ppm
  • Mist
  • Fan
  • Light

Light runs 07:00 to 19:00, the exhaust fan runs the first fifteen minutes of every hour, and the controller switches the mist on below 85% and off above 90%. Values are a simulation of how the parts behave, not readings from a real grow.

Shows the part's description in the panel beside the diagram.

Why automate

Fruiting conditions drift, and people check at the wrong times

A tent does not stay where you left it. Mist raises humidity for a few minutes and then the air dries back out. Mushrooms breathe out carbon dioxide all day, so a closed tent climbs toward the point where oysters grow long stems and tiny caps. The room cools at night and warms in the afternoon. None of this happens on a schedule you can keep by hand.

So most of us land in one of two habits. Checking too often, which means opening the tent every hour, dumping the humidity you built up and misting by eye. Or checking too rarely, which means finding dry pins and a stalled flush after a weekend away.

Automation fixes the timing. A controller mists when the probe says to, a timer runs the fan and light whether you remember or not, and you spend your attention on the mushrooms rather than on the hygrometer.

What to control

Four things, in order of how fast they go wrong

Each range below is general guidance from extension programs and standard cultivation references, with the date it was checked. Strains vary, and the mushrooms always get the final vote.

  1. Humidity

    Fruiting mushrooms are mostly water and lose it to the air constantly. Most gourmet species pin and fruit above 85% relative humidity and tolerate a drop into the 80s once caps have formed.1 Humidity changes in minutes, which is why it gets a controller rather than a timer.

    60 % 85 95 %

    Relative humidity, fruiting band marked

  2. Fresh air exchange and CO2

    The mycelium and the mushrooms respire, so CO2 rises in a closed tent. Cornell's guidance is to keep most species under 1,000 ppm and oysters under about 800, with an air change every five to ten minutes.1 Too little fresh air shows up as long stems and small caps. Too much dries the pins.

    400 800 1,000 2,000 ppm

    CO2 in the tent: 800 for oysters, 1,000 for most species

  3. Light

    Mushrooms do not photosynthesise. Light tells them which way is up and when to form caps. If you can read a book comfortably in the tent, there is enough.1 Low light produces skinny, long-stemmed mushrooms. A low-heat LED on a day and night timer covers it.

    enough to read by dark bright

    Indirect light on a 12 hour schedule

  4. Temperature

    The slowest to change and the hardest to fix with a plug-in device. Many species fruit best in the low 60s °F, roughly 16 to 18 °C, with productivity falling below about 10 °C and above about 24 °C.1 Choose the room first, then let the controller handle the rest.

    5 °C 10 16 to 18 24 30 °C

    Room temperature, most species on this page

Typical fruiting ranges by species

Typical fruiting ranges for common gourmet species
Species Fruiting temperature Relative humidity CO2 Light Sources
Oyster Pleurotus ostreatus 10 to 21 °C50 to 70 °F 85 to 90 % under 800 to 1,000 ppm Indirect, 12 h on 2 1 4
Shiitake Lentinula edodes 13 to 18 °C to pin55 to 65 °F to pin 85 %+ to pin, then 60 to 80 % under 1,000 ppm Indirect, 12 h on 3 4
Lion's mane Hericium erinaceus 10 to 18 °C50 to 65 °F 85 to 95 % 500 to 1,000 ppm Low to indirect 4 1
King oyster Pleurotus eryngii 10 to 18 °C50 to 65 °F 85 to 90 % under 2,000 ppm; higher CO2 lengthens the stem Indirect, 12 h on 4
Pink oyster Pleurotus djamor 20 to 30 °C68 to 86 °F 85 to 90 % under 2,000 ppm Indirect, 12 h on 4

Ranges checked 2026-10-22 against the sources listed at the end of the page. They describe fruiting, not spawn run, which wants warmer, darker and higher-CO2 conditions. Pink oyster is the warm outlier; everything else here likes a cool room.

The parts

What each piece does, described generically

No brands and no prices. Any device that meets the description will do the job; the fit between parts matters more than the badge on them.

  • Humidifier

    An ultrasonic humidifier or fogger with a tank you can refill without opening the tent. It should push mist through a hose or a short duct so the fog enters above the top shelf and settles. Cool mist only; warm-mist units heat the air you are trying to keep cool.

  • Humidity and temperature controller

    A box with a probe on a lead and at least one switched outlet. You set a low and a high threshold and it turns the outlet on and off between them. Some read temperature and have a second outlet for a heater or cooler. Look for a probe lead long enough to reach mid-tent.

  • Timer or smart plug

    A mechanical or digital outlet timer with at least fifteen-minute resolution, or a smart plug with schedules. It runs the light on a day and night cycle and the exhaust fan in bursts. A smart plug adds a log of when things ran, which is useful when a flush goes wrong.

  • Exhaust and intake fans

    A small fan mounted high pulls stale air out; an intake low on the opposite side lets fresh air in. Many home builds use a computer-style fan on a USB or 12 V supply. A filter or fine mesh over the intake keeps dust and insects out without blocking airflow.

  • CO2 sensor

    An NDIR sensor, which measures CO2 directly rather than estimating it from other gases. On a simple build it is a readout you glance at; on a DIY build it feeds a microcontroller or hub that switches the fan. Place it mid-tent, away from the intake and the mist.

  • Light

    A low-heat LED strip or bulb in the 5,000 to 6,500 K range so the colour reads as daylight. Brightness is not critical; even indirect light is enough for mushrooms to orient and cap. Mount it so it does not shine straight onto the probe and warm it.

Build levels

Three ways to build it, each one a complete setup

Start where your patience and your room allow. Each level works on its own, and each one keeps the parts from the level before.

  1. 1Level one

    A timer and a humidifier

    The humidifier runs on the timer in short bursts, say five minutes every hour, and the light runs on a second timer or the same one. Fresh air comes from opening the tent once or twice a day, or from a passive gap.

    • Fixes the forgetting problem and nothing else.
    • Humidity swings with the room, so you still read a hygrometer and adjust the burst length.
    • Good first step for one or two blocks.

  2. 2Level two

    A plug-in controller

    The humidifier moves to a humidity controller with a probe in the tent. The timer now runs the exhaust fan and the light. The controller holds humidity in a band regardless of the weather in the room.

    • Mist happens when needed rather than on a schedule.
    • The fan on a timer gives steady fresh air exchange; CO2 is managed, not measured.
    • The level most home growers settle on.

  3. 3Level three

    A DIY sensor setup

    An ESP32 or a home-automation hub reads a humidity and temperature sensor and an NDIR CO2 sensor, switches relays for the mist, fan and light, and logs everything to a dashboard you can check from the kitchen.

    • The fan runs when CO2 climbs rather than on a guess.
    • A history of every flush, so you can see what changed when a flush went well or badly.
    • Needs soldering or at least careful wiring, and a willingness to debug.

added at this level kept from the level before

Safety

Water, electricity and spores share a small space

None of this is exotic. It is the same care you would take with an aquarium or a bathroom fan, applied to a tent that is wet on purpose.

  • Electricity near water

    Plug everything into a GFCI outlet or a GFCI adapter. Keep power strips, timers and the controller above the humidifier's water level and outside the tent. Loop cords so a drip runs down the loop and onto the floor, not into a plug.

  • Mould and spore exposure

    A fruiting tent releases spores, and some people react to them with coughing or allergy symptoms. Vent the exhaust toward a window or out of the room where you sleep. Harvest before caps flatten fully, and wear a mask when you harvest a large flush or clean up.

  • Cleaning

    Empty and dry the humidifier tank between fills and descale it on the maker's schedule; a dirty tank sprays whatever grows in it into the tent. Wipe the drip tray and the cover when you change blocks. Use distilled or filtered water if your tap water leaves white dust.

  • Contamination control

    Green or black mould on a block is a signal to remove that block from the tent, not to mist more. Bag it, take it out of the room and clean the shelf before the next block goes in.

Common failures

What the mushrooms are telling you, and what to change

Read the symptom first, the way a field guide reads a leaf.

  • Long stems, small caps

    Not enough fresh air

    CO2 is high. Run the exhaust fan longer or more often, check that the intake is not blocked, and make sure the fan is actually moving air out rather than stirring it.1

  • Skinny, leaning mushrooms

    Not enough light

    Mushrooms stretch toward whatever light they can find. Add a light or move it so every shelf is lit, and run it on a consistent day and night schedule.1

  • Dry, cracked caps or aborted pins

    Humidity drops between mist cycles

    Narrow the controller's band, move the probe closer to the blocks, and check whether the fan is running so long that it strips the humidity the mist just added.

  • Wet, soggy blocks and water pooling

    Too much mist landing on the blocks

    Aim the hose so fog enters above the top shelf and drifts down rather than spraying the blocks. Raise the low threshold a little less aggressively, and empty the tray.

  • Controller mists constantly

    The probe is in the wrong place or the tent leaks

    A probe in the fan's airstream reads dry and asks for mist forever. Move it mid-tent. If the tent has a gap at the zipper or the hose entry, close it; the humidifier should not be humidifying the whole room.

  • Readings jump around

    Sensor placement or a cheap hygrometer

    Compare the probe with a second hygrometer in the same spot. Some consumer hygrometers read several points off at high humidity. Keep the probe out of direct mist and out of the light's heat.

  • Flush stalls, nothing pins

    Temperature or no trigger

    Most species here want a cool room to pin. Check the temperature over a full day, not once. Some species also want a shock: a drop in temperature or a soak, depending on the species. Spawn run conditions and fruiting conditions are different jobs.

  • Everything runs, nothing logs

    Smart plug or hub lost its connection

    Give the hub a fixed address on your network and a schedule stored on the plug itself where possible, so the fan and light keep running when the wifi drops.

Sources

Where the ranges come from

  1. 1Cornell Small Farms Program, "Seven Stages of Cultivation", in Methods of Commercial Mushroom Cultivation in the Northeastern United States. Fruiting temperature in the low 60s °F, humidity above 85% then the 80% range, CO2 under 1,000 ppm (oysters under 800), an air change every five to ten minutes, and the book-reading light test. smallfarms.cornell.edu checked 2026-10-22
  2. 2Hameed, Cotter, Liao and Hsu, D.I.Y. FunGuide: Grow Your Own Oyster Mushrooms at Home, UF/IFAS Extension SL448/SS662. Fruiting chamber at about 20 °C and 90% humidity with good air exchange and light on a day and night interval. edis.ifas.ufl.edu checked 2026-10-22
  3. 3Lyon, Amante, Londo and Toland, Shiitake Mushroom Production: Fruiting, Harvesting, and Storage, Ohio State University Extension F-0042 (2022). Pinning at 55 to 65 °F with relative humidity of at least 85%, light required for fruiting; written for outdoor logs. ohioline.osu.edu checked 2026-10-22
  4. 4Paul Stamets, Growing Gourmet and Medicinal Mushrooms, 3rd edition (Ten Speed Press, 2000). Growth parameter tables for Pleurotus ostreatus, P. eryngii, P. djamor, Lentinula edodes and Hericium erinaceus: fruiting temperature, relative humidity, CO2, fresh air exchanges per hour and light. Print reference. checked 2026-10-22