As the majority of water absorbed by mushrooms comes from the compost its logical that mycelium quality in the casing soil must be excellent throughout the entire cultivation process. This mycelium must ensure that water from the compost and nutrition is transported freely to the growing mushroom.
Paying sufficient attention to mycelium quality is therefore an essential aspect of growing from the very early stages beginning with the type of casing soil. A rougher textured wetter casing soil generally gives better mycelium quality as the moisture retention properties are better. No mycelium can grow where there is water and the quality of mycelium in casing soil often deteriorates as the quantity increases.
For certain reasons some growers prefer to use a finer textured casing soil. In this case regular sprinkling is essential to increase water retention. A finer drier casing soil can also be more heavily compacted to prevent too much water being lost through evaporation.
In the run up to the first flush problems seldom occur with mycelium quality. Afterwards if the casing dehydrates too much the mycelium in the casing soil will also dehydrate and may threaten to choke the casing soil. The quality of later flushes will deteriorate.
The only way to keep this problem in check is to keep the moisture content of the casing soil in balance. The casing soil must not dry out too much at any point during the growing process as recovering the moisture level after a period of dehydration is very difficult if not impossible. Keeping moisture at the required level can be done in two ways: sprinkling and preventing unnecessary evaporation.
John Peeters, C point