CULTIVATIONTIPS JOHN PEETERS
Spraying the floor of the growing room is a simple way of increasing the humidity.
Picture: John Peeters
Humidification in winter According to the famous Mollier diagram, air of 0° Celsius can
hold a maximum of just under 4 grams of moisture/water per kilogram. If you look at the temperature and moisture contents customarily used in mushroom growing, this leads to a figure of between 10 and 11 grams of moisture per kilogram at 17° Celsius and 85% relative humidity. So, with low outside temperatures, a high demand for humidification is created. This need will partly be met by evaporation from the compost and the casing soil. However, at temperatures of 0° or lower, these sources are far from enough, and the compost and casing will dry out even more due to the high level of natural evaporation. In addition, without extra humidification, the mushrooms that appear will show signs of scaling, simply because the outside air - even though heated - still contains a maximum of between 3-4 grams of moisture when it flows into the growing room. This means humidification is necessary. But, in winter especially, what is the best approach?
Steam seems to offer the best solution. A small pipe behind the fan adds a little steam to humidify the dry, heated air flowing into the growing room. In summer, when the outside air is coo- led, any steam humidification necessary will not be very effec- tive. In this case, the air entering the growing room is often already saturated with moisture so any extra steam added to it will make it ‘rain’ because the air cannot absorb any extra moisture. Extra humidification using steam is hardly ever
necessary in summer. But, in winter, when the incoming air is low in moisture, steam is very effective. A major disadvantage of using steam is that the boiler must be kept under constant pres- sure, which will push up the gas bill. On smaller-scale farms, which maybe only cook out one growing room (empty) a week, using the boiler is reserved for this purpose, otherwise the cost of gas or oil will be sky high - something that has to be avoided in these difficult times.
Another way of increasing the humidity is to simply spray the floor with water. Take care not to spray the floor continuously, otherwise it will function like an immense cooling coil, and in extreme cases reduce the humidity. It’s best to spray the floor 3-5 times a day and then let it dry. This ensures the moisture on the floor is gradually absorbed by the growing room air, so it has an effective humidifying action. Slightly more heating will be needed, but this humidification method is good for the quality of the pinheads and the mushrooms. You can use your usual watering system with additional nozzles to spray the walls and floor and automate the humidification process in this way. Or just take a hose and spray the floor in the growing room, making sure the floor is wet evenly everywhere. Another option is to install a sprinkler pipe under the beds and wet the floor at regu- lar intervals by setting a timer. To set the right interval check the situation. If the floor is starting to dry but is not yet fully dry, you can start spraying water again.
44 MUSHROOM BUSINESS
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