In very dry periods such as now in the Netherlands its difficult to keep relative humidity (RH) in the growing rooms high. Various measures are needed to keep a high RH in the growing room if the moisture content of the outside air is extremely low.
Firstly the C02–content must be kept as high as possible. The maximum CO2-content in a growing room with mushrooms on a bed is 1800 ppm. If CO2-content values are higher the effect on mushroom quality is detrimental causing them to discolour more quickly.
If a high RH cannot be reached, it's better to let the RH drop a little too low and create a more stable climate in the growing room with less circulation to keep the microclimate in good shape. The RH can be allowed to drop lower by setting greater margins.
If the RH drops too low, ie an average of more than 3 % lower than normal, only then activate steam humidifying. A big disadvantage of steaming to create humidity is the spread of moisture in the growing room and possible condensation of steam on the bed and pinheads. Before picking its better to humidify the growing room by keeping the walls and floor wet.
Mark den Ouden, C point