The conclusion of a previous experiment showed that the compost quantity was the most determining parameter for the production volume of mushrooms, despite the addition of hemi cellulose as carbon source to the compost. The present experiment focuses on the mycelium action with regard to the carbon availability in the compost. Two factors were studied: (1) The effect of breaking the mycelium at a predetermined depth in the compost layer and before the first mushrooms flush. The hypothesis was that mycelium which is no longer in contact with the mycelium in the casing material would free the carbon nutrition in the lower compost layer. This increased amount of free carbon would be beneficial during the budding. It was expected that breaking the compost layer during the growth of the mycelium would increase the amount of buds. The observed effect of breaking the mycelium is that the formation of buds is delayed in comparison with the reference. (2) The effect of distributing the compost in a longer layer which remains partly uncovered by casing material. The compost is distributed into a thin layer with 2-3 times the surface area of the reference. The casing material just covers the same surface area of the compost as in the reference. The hypothesis is that the mycelium can exploit the total extended compost layer and increase the mushroom production in correlation with the volume of compost accessible, but independent of the surface of the casing material. The observed effect is that the longer the compost layer is, the lower the production gets. In summary, the depth of the compost layer is the most determining factor for yield.