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Lesson 1 / 5 · Controlled Environment & Climate

Air & Compost Temperature

A grow room does not have one temperature. It has at least three, and the one on your wall thermometer is usually the least important of them.

  • By the end you can name the temperatures a mushroom room actually has.
  • By the end you can quote stage bands for a controlled button crop.
  • By the end you can treat a temperature ceiling as a disease threshold.

Room climate by crop stage

Air and compost temperature bands for each stage, with the ceilings that are disease limits.

10°C15°C20°C25°C30°CSpawn run22-25°C85-95% RHCase run23-25°C90-95% RHPinning16-18°C85-90% RHCropping15-18°C80-85% RH
Temperature bandRelative humidity

Read numerical examples with their source, method and crop context. They are not universal operating instructions. Historical prices are not current quotations.

Spawn run air22-24°C23 plus or minus 1 C in the room airSource: ICAR-DMR manual, 2011
Bed above air1-2°COyster beds run 2 to 4 C aboveSource: ICAR-DMR manual, 2011
Fruiting air15-17°COther DMR tables give 14 to 16 and 14 to 18Source: ICAR-DMR manual, 2011
Crop heat load10W per m2Bed area, first two flushesSource: ICAR-DMR manual, 2011
Air handler exit air14°CAt full humidity, to give 17 C at the bedSource: ICAR-DMR manual, 2011
Spawn run ceiling26°CAbove this false truffle risk risesSource: NHB DPR model, 2018
Educational grow-room illustration showing separate crop and room measurement locations.
AI-generated teaching illustration · not field evidence
Connect the picture to the lesson

Air versus bed

Notice
Air and growing material are different measurement locations.
Understand
An active crop releases heat; the wall display is not every bed's temperature.
Try it
Map probes, sensor locations and representative crop readings.
See where this fits in the full workflow →

01Three temperatures, not one

Room air is what a wall thermometer reads. Bed or compost temperature is what the crop actually lives in. Outdoor design temperature is what your cooling plant has to fight.

ICAR-DMR keeps these separate. For button spawn run it holds the room air at 23 plus or minus 1 C, and states that this corresponds to a bed temperature of 24 to 25 C, one to two degrees higher. For oyster it reports bed temperature generally 2 to 4 C above room temperature.

That gap is not an error. The compost is alive and making heat. If you set the room to the crop number, the crop sits above it.

02The bands by stage

Using button mushroom as the worked example, the 2011 manual gives a ladder. Spawn run: air 23 plus or minus 1 C. Case run: 24 plus or minus 1 C. Then cropping: the air is brought down to 15 to 17 C.

DMR's other documents give other fruiting figures: 14 to 16 C in one table, 14 to 18 C in the seasonal folder, 16 to 18 C in the Hindi farmer folder. These are all ICAR-DMR.

The lesson is not that one is right. It is that a band published for a controlled room, a seasonal shed and a species table are three different claims.

03The crop is a heater

DMR quantifies it. During the first two flushes a button bed gives off about 10 watts of heat per square metre at 17 C and 88 percent humidity, along with its carbon dioxide.

That is why a room cannot be held at one temperature by one setting. Air warms as it crosses the beds, so the far end of a long room runs warmer than the near end.

DMR gives the engineering answer for its own rooms: to obtain 17 C and 85 percent humidity at the bed, air leaves the air handling unit at 14 C and 100 percent humidity. The supply air is deliberately colder than the target.

04Ceilings that are disease thresholds

Some numbers are not preferences. False truffle appears above 23 C, and NHB, reproducing ICAR guidance, says avoid temperatures above 26 to 27 C during spawn run and after casing, and keep cropping below 18 C.

Blotch needs 20 C or above with water on the cap. DMR ties olive green mould to pasteurisation above 60 C. At the end of a crop, a cook out at 70 C held for 12 hours kills pathogens in the compost.

So when you write a set point, write beside it whether it is a preference or a limit. Only one of those two can be traded for electricity savings.

Map your room against its own crop

  1. Put one thermometer in the room air and one probe in the bed.
  2. Read both at the same minute, morning and evening, for a week.
  3. Note the gap between them and how it changes with the flush.
  4. Read the far corner of the room as well as the near one.
  5. Write your set point beside the DMR band for that stage.

Write in your farm diary: Date, time, air reading, bed reading, corner reading, stage of crop, and any set point you changed.

Mistakes that cost a crop

  • Setting the room to the crop number, which leaves the bed above the band.
  • Reading one thermometer near the door and calling it the room.
  • Treating a disease ceiling as a comfort target that can be relaxed.

Check yourself

Three questions, instant answers

  1. Why is the compost warmer than the room air?

  2. DMR delivers 14 C air to hold what at the bed?

  3. What kind of number is the 26 C spawn run figure?

An editorial self-check, not a certificate. Answers are not stored, not even on this device.

Words used in this lesson

Set point
The value you ask the controller to hold.
Bed temperature
Temperature measured inside the compost, not in the air.
Cook out
Heating a finished crop to kill pests and pathogens.
References & further reading
Climate and production-room knowledge system

Biological requirements are not equipment selections.

Open current reference
The guide behind this lessonOpen the reference guide