The most important thing to do is not “shut down” your greenhouse
It is imperative that the exhaust fans be allowed to run during the summer to prevent excessive build-up of heat. Temperatures inside an enclosed greenhouse with no ventilation during summer months can reach in excess of 140 degrees. At these temperatures, the thermostats or controllers as well as any plastic materials such as irrigation, NFT troughs, etc. will be damaged and most likely need to be replaced upon your return. Additionally, make sure that the shutters and or wall vents are fully open as to not restrict the fans air movement.
The thermostats or controller can be adjusted to a higher setting than is desired during the growing season to help minimize electrical usage during this season. The idea is to only provide a minimal amount of ventilation to avoid extreme temperatures. Since it’s not necessary to run the evaporative cooling system during this time, it’s a good idea to drain the trough of the evaporative cooling system to help avoid algae build up.
It’s a good idea to remove any remaining plant material and give the greenhouse a good cleaning. The use of a disinfectant will kill or reduce any pathogens that may have developed. Lastly, perform a thorough walk through to be sure that there are no stray animals that will become trapped inside the greenhouse. They will surely not survive.
Following these few steps keep the greenhouse in good running condition and ready for a successful new year upon your return.