How to steer pinhead development

A good spread during the first flush gives much higher production. But during pinhead out grow how can growers steer towards precisely the right number of pinheads and development of different cap diameters? Let me explain how.

The height of mycelium colonisation

The moment of cool down and the days immediately following determine how far the mycelium grows up towards the surface of the casing soil. The whiter the surface of the casing, the better and the more pinhead formation you will notice. Pinheads will be less visible the deeper they have developed in the casing soil. Measures are often applied to reduce the number of pinheads if the surface is whiter as all the pinheads are visible. But not all these pinheads will grow into mushrooms anyway. The reverse applies if you cannot see the pinheads, so beware in this case! After all, the pinheads are just below the surface where they are well protected and will all develop into mushrooms. Conclusion: if recovery growth appears weaker – i.e. the surface of the casing is darker – more pinheads will always develop than you expect compared with a casing that appears whiter.

How can you inhibit pinheads?

Increasing the CO2 content (the so-called CO2-shot), increasing the RH or the temperature are ways of inhibiting pinhead formation. My experience is that CO2 has 10% influence on pinheading, RH 20% influence and 70% influence is caused by the temperature. In addition, the room air temperature is associated with the lowest risk of poorer quality compared with adjusting with RH and CO2 settings.

Air temperature

If the room air temperature (AT) is increased by half a degree for 24 hours the larger pinheads will grow faster, growth of the smaller ones will stagnate and the very small ones will die. Reset the air temperature to the original setpoint after 24 hours. You can repeat this process after 24 hours. The first pinheads will appear 5-6 days after cool down. You can ‘play’ with the air temperature from the moment the pinheads are literally the size of a pinhead up to the moment the largest mushrooms are around 2 cm. How exactly the pinheads respond is a matter of experience.

What you will see is that the difference in temperature multiplied by the duration of the adjustment is what gives results. As an example: theoretically increasing the AT by 1 degree for 12 hours gives the same results as increasing the AT by half a degree for 24 hours.

Mark den Ouden

mycelium fails mushroom growth


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