How HOT it was

Dutch CHAMPIGNONCULTUUR 1964-7
A writing by husband Pieter at the BEGINNING of mushroom growing.
Nowadays, almost every mushroom farm has complete airconditioning. 
You sure will understand WHY, when reading these struggles for survival back then!

Vaguely you can read to the right; mush room...
How hot it was

For many mushroom growers, the warm weather of the past period has caused quite a bit of damage. The extent of this damage was illustrated by the greatly reduced supply of mushrooms at the auctions.
At eight auctions e.g. the total average weekly supply in the month of June and the first weeks of July was around 50,000 kg. In the week from 20 to 27 August, that supply suddenly dropped to about 27,000 kg. In the following week, the supply increased again to about 42,000 kg.
A damage of many thousands of kilograms. The strange thing, however, is that there were also a number of growers who have experienced much less or even hardly any disadvantage from the heat. We therefore thought it would be good to take stock of the last summer period to see if there is anything to learn from.
One thing has become clear, namely that most buds have not died due to excessive temperature, but above all because of too high CO₂ levels of growing room air; in combination with a too high temperature. One cannot be separated from the other; when the temperature in the growing room rises, the mushroom mycelium will grow faster. An enlarged activity of the mycelium means that more carbon dioxide is formed and the temperature in the beds increases. This higher bed temperature stimulates the activity of the mycelium again and thus we enter a spiral where one unfavorable factor evokes or strengthens the other.
If the temperature outside is soaring, a mushroom grower can do two things. He can ventilate at night with cooler outdoor air and keep the rooms closed during the day and circulate only to shut out the heat. This means that the room temperature may remain several degrees lower, but it also means that there is no ventilation during almost the entire day. This is despite the fact that CO₂ production, due to the always high temperature, is extra large.
Growers who act in this way often saw that the mushrooms, despite a slightly lower room temperature, still died off, due to lack of ventilation. It has yet to be said that there are also growers who cannot circulate during the day because they do not have air mixers.
A second possibility is; ventilate as much as possible at night (we saw a fan in each doorway) and only at the hottest hours of the day limit ventilation, but keep circulating. Although the temperature in the rooms may be several degrees higher in this course of action than in the first case, the damage is much lower.
In other words, a temperature of e.g. 20ºC in a sufficient ventilation seems to do less damage than 18ºC with insufficient ventilation, i.e. too high CO₂ levels.
The effects of high temperature and insufficient ventilation further seem to be greater when compost and casing are rather on the wet side. Fortunately, 'Ottersum' delivered the compost a little drier in the past period and at this point there were no problems. As far as the casing material is concerned, it turned out to be good in general, and especially between breaks, 

to water a little less, especially after the third break.
The dehydration that occurs when ventilated at night with a fan in each doorway, of course should  be compensated with a little extra watering.
For the first time, and therefore more or less experimentally, a cooler has been installed by some growers in order to keep the room temperature sufficiently low. The first experiences seem to be good. In addition to the lower room temperature, the more or less dehumidifying of the air (which occurs automatically when air is cooled to a certain temperature) appears to work favorably. Some claim that the mushrooms on the beds turn black when the temperature of the inlet air is too low. Furthermore, there is little experience with this matter. The Experimental Station also has such a refrigeration device; As soon as we have gained some more experience, we will come back to this.
Some growers kept the roof on the mushroom farm constantly wet during the warmest days by means of a sprinkler system. Thus it proved possible to keep the temperature in the growing rooms several degrees lower. One can imagine this; such a large roof surface captures a mass of radiation heat and although the ceilings should be extra well insulated, the temperature in the space above the ceiling will certainly affect the cell temperature.
There was also a palpable difference in temperature of growing room exterior walls that were in direct solar radiation as opposed to room walls in the shadow of trees. Also, there is noticeable difference in temperature between normal and whitewashed mushroom farm walls. A dark color of the outer walls causes the heat rays to be absorbed.
We even heard from a grower who had the plan to chalk up the roof of the mushroom farm as market gardeners do with their greenhouses.
We can imagine that it matters a few degrees.
When the warning message of the K.N.M.I. in De Bilt (Dutch weather station) is being announced over the radio next year, we could, based on this year's experience, do the following:
At night and especially in the cool morning hours (this is from 3 to 5 AM) ventilate as wide as possible with everything open. Fans placed in the doorways can promote the flow of cool air. The flow seems to be better when the air mixers in the rooms are stopped.
During the day, limit ventilation, but do not completely close the rooms so that some ventilation remains possible. During the day, the air mixers keep running constantly.
In general, and especially between breaks, give slightly less water. Especially also make sure that the compost is not too wet after pasteurization, better even something on the drier side.
You may be able to do one or more of the things mentioned, whitening the mushroom farm, keeping the roof wet or chalking it.
Soon it will be time to look out for an ascending planting, e.g. of Italian poplars, on the sun side of the mushroom farm.
P.J.C. Vedder

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