Milky mushroom:
temperature, humidity
and CO₂

Most cultivated mushrooms prefer the temperatures of a hill station. Milky mushroom does not. It was domesticated in India, it fruits in the heat that stops button mushrooms and slows oyster, and it keeps well after harvest. For growers in the plains it is the natural crop for the hot months.

It also has a particular ventilation problem, and that is what this guide is mostly about.

Conditions at each stage

Published timings vary between institutes and methods: the whole cycle runs roughly six to nine weeks from spawning. ICAR-IIHR gives a biological efficiency of 50–100%. Freshly harvested milky mushrooms keep 2–3 days at 25–30°C and 10–15 days at 4°C, far longer than oyster.

Casing

Like button mushroom and unlike oyster, milky mushroom will not fruit well without a casing layer. TNAU guidance uses sterilised (steamed) garden soil, a clay loam of around pH 8, sometimes mixed with 2% calcium carbonate, spread 1–2 cm deep over the opened bag; other guides use 2–3 cm. The mycelium must grow up through the casing before pinheads appear on its surface.

What CO₂ does milky mushroom need?

The institute guides specify “ventilation” for cropping rather than a ppm figure, so treat any exact number with care. The pattern is the same as for other cultivated mushrooms:

• During spawn run, the bags are closed and CO₂ inside them is high. That is normal and helps colonisation.
• During cropping, the forming mushrooms need fresh air. High CO₂ gives the familiar signs: long stems, small caps and slow, uneven development. Many growers aim to keep the cropping room below about 1,000 ppm, the same working target used for oyster.

If you see long stems and small caps in cropping, check CO₂ before blaming the spawn. More on that in why mushrooms get long stems and small caps.

The summer ventilation problem

A milky mushroom cropping room needs three things at once: high temperature, high humidity and fresh air. In an Indian summer, the fresh air is the problem. Outside air on a May afternoon can be hotter than the room and far drier, so every minute the fan runs pulls humidity down and pushes temperature up.

Growers respond in one of two ways, and both cost yield:

• Ventilate on a generous timer and fight the drying with more water. Surface moisture on the casing rises, humidity still dips during each run, and caps can crack.
• Keep the room shut to hold humidity. CO₂ climbs, and the crop stretches.

The way through is to ventilate only as much as the crop actually needs, when it needs it:

1. Measure CO₂ among the bags during cropping for a few days. You will see when it climbs and how fast.
2. Run the fan on CO₂, not a clock. Set a Fan ON threshold at your upper limit and a Fan OFF a few hundred ppm below. The fan runs in short bursts only when the room needs air.
3. Watch humidity alongside. If RH drops sharply with every burst, run the humidifier over the same period.
4. Check temperature, too: milky mushroom tolerates heat, but a room that goes well above the cropping band during afternoon ventilation is telling you to shade the inlet or ventilate from the cooler side of the building.

The short version

Milky mushroom wants heat, humidity and fresh air all at once, and in an Indian summer the fresh air works against the other two. Colonise in closed bags at 30–35°C, case with sterilised soil, crop at 35–38°C and 85–90% RH, and ventilate the cropping room on measured CO₂ so it gets the air it needs and no more.