‘They're growing too fast’ - a frequently heard remark on the third picking day of the first flush. The supervisor thought enough had been harvested the day before, but then it all starts. On the morning of the third day everything seems in order, but as the day progresses the stalks become wet, the caps soft and the mushrooms quickly start shooting up in height. The quality rapidly deteriorates and more mushrooms have to be picked than intended.
The cause is not the amount picked on the second day, but the picking pattern on the first day. Mostly only the pre-pinners are removed and therefore only larger mushrooms. This causes the formation of clusters of mushrooms, between which a too high CO2 content is created on the third day.
On the first picking day, small mushrooms should also be removed as well as mushrooms that would be too large the following day. The other mushrooms of average size and a few larger mushrooms can be left on the beds. This encourages a range of various sized mushrooms right from day one. But, this can only be achieved by also removing the small mushrooms on the first picking day. Thinning in this way prevents the compost temperature rising too quickly and the CO2-content between the mushroom clusters becoming too high. The down side is that the first picking day takes longer. Plus, it's very difficult for pickers to harvest small mushrooms and leave the larger ones behind.
Henk van Gerwen, AdVisie ‘The mushroom cultivation advisors’