Pinning

Mycelium forms mushrooms when its surroundings change from the sealed, dark, CO₂-rich conditions of colonization to the conditions near a forest floor surface. Three signals do most of the work: carbon dioxide falling (from fresh air exchangeFAEFresh air exchange: swapping the stale, carbon-dioxide-rich air in a container for room air.), light, and a surface that stays humid while still letting a little water evaporate. A modest temperature drop helps some growers but is not required for cubensis.

The first visible sign is hyphal knotsHyphal knotsTiny dense white specks on the surface, the very first step toward pins., tiny dense specks. Over a few days they grow into pinsPinsBaby mushrooms a few millimetres tall, the first visible stage after hyphal knots., also called primordiaPrimordiaThe formal name for pins: the earliest mushroom bodies, before cap and stem are clearly separate., with a cap and stem starting to show.

Air temperature

About 70–78 °F (21–26 °C); steady matters more than exact

Humidity at pin set

High: 90–95% in the air, near saturation right at the surface

Fresh air

Enough to keep CO₂ low; many growers aim under about 1,000 ppm

Light

12 hours on, 12 off, indirect daylight or a 5,000–6,500 K bulb (Bible, p. 53)

Days to first pins

Usually 5–10 days in bulk; PF cakes can show pins within days (Bible, p. 112)

When to change anything

Hold steady until pins are pea-sized, about 3–5 mm

1. 1.Uncover the tub's holes, or open the AIO bag or move cakes into a fruiting chamber.
2. 2.Give it light on a 12/12 cycle. Indirect daylight is enough; very little blue light is needed to start pins.
3. 3.Check the surface. You want fine droplets like morning dew that slowly come and go. If it goes matte, mist the walls and lid lightly, never straight onto the surface.
4. 4.Fan gently once or twice a day if the container has no passive airflow. Do not aim moving air straight at the surface.
5. 5.Then mostly leave it alone. Every change you make now is a disturbance.

Experienced growers judge pinning by the surface, not a number. A matte, dull surface means it is drying out, and pins will stall or abortAbortsPins that stop growing while their neighbours keep going; their caps darken to brown or black within a day or two.. Pooled water or big beads that never evaporate mean it is too wet and stale. The target sits between: a fine sheen of droplets that appears, slowly fades, and returns after a light wall mist. Cheap humidity sensors drift by a few percent above 90% RH anyway, so treat their readings as a rough guide.

Humidity and fresh air work against each other. Each burst of fresh air also removes moisture, so a container with lots of airflow needs more water from somewhere, whether a damp perlite floor, a casing or wall misting.

When most pins reach pea size, the book model lowers humidity slightly, into the mid-to-high 80s, and adds more fresh air, because some evaporation helps young mushrooms mature (Mushroom Cultivator, p. 144). In practice that means opening up a little more and never letting air blow straight at the pins. The fruiting guide covers the days from here to harvest.