The filling weight, i.e. the number of kilos of compost per square metre, should be between 80-95 kg/m2. The general trend is the more compost, the better the mushroom quality. But is that right?
Mushroom growing is all about the difference between air temperature and compost temperature, referred to by growers as activity. Activity is essential to grow good quality mushrooms. As the compost is warmer than the air, moisture is released in the form of evaporation. This caused the mushrooms to grow.
Managing activity is key to mushroom growing. So too much activity, because the filling weight is too high, results in faster, uncontrollable growth. For example, a first flush that produces 8 to 10 kg/m2 of mushrooms on the third day. The quality has been lost. The compost temperature has risen too quickly to 25-26 degrees Celsius. So any added value of filling that extra kilo of compost has been wasted. Say you had filled 90 kg/m2 of compost. In that case a filling weight of 85 kg/m2 would have been a better choice. This makes it easier to manage and control activity.
The casing soil on the compost plays a significant role here. The more activity there is, the more the casing soil dehydrates. This means that more mycelium grows in the casing soil. Dried out casing soil cannot absorb water, and neither can mycelium. What is left is dry casing soil that disrupts the water transport from the compost to the mushrooms. The casing soil effectively acts as insulation blanket. So there is activity, but little growth.
I see the highest yields and the best quality, from the first to the third flush, in situations where compost activity is well managed and controlled and the casing soil stays soft and wet.
Mark den Ouden | Mushroom Blog