Europe is now at the time of the year summer will burst out. And every year the same growing problems occur at this time, getting worse and worse every year. Summers seem to get hotter and it is time to adapt before real growing problems are there. There are a number of things growers can do but of course a good cooling system is a must. Well calculated, fitting the circumstances of your own country. But even the best cooling system will not cover everything. If we take the summer temperature last year in Holland at 42° nobody has a cooling system which will handle these extreme temperatures in our country.
If at the same moment also the relative humidity is high it is not only cooling but also the heating that counts. And that brings me to the first mistake many growers make. In summer switch of the heating system. Its hot enough outside, I do not need heating. Wrong!!!

De-humidification only works if the cooling can work in combination with a bit of heating. So, by switching of the heating the system can make the air dryer anymore. And you need dry air to cool a hot room. The easiest way to cool a growing room is to give water to the casing soil. The best way is to give many small quantities up to 2 litres. That can be evaporated again. Spread the watering over 24 hours. The dry air coming into the room will take care of the evaporation and will help cooling the growing room. Keep the casing soil wet but the floor as dry as possible. That is why I do not close the room completely if the outside is hot but dry. It is possible to use air which is much higher than the compost temperature as long as the incoming air is dryer than the air in the room.

In the mollier diagram one can calculate how much fresh air is necessary to absorb the evaporated water in the room. And for that cooling by evaporation you only need a few litres of water extra. No extravagant quantities as some growers tend to do. An extra help will be some mobile coolers on the farm. They can be placed into the room just before the heat surge is starting. The price of such a mobile cooler is a lot lower than the costs of losing a room.But in the end, judging a room is important. If compost is active and the C/N ration is relatively high one can expect activity. It is of outmost importance that cooling starts before the surge starts. Once a compost is going up it is hard or impossible to stop it.