To grow strong resilient crops we need to empower the plants to bring the needed elements to support this building process. We can do this easily by making sure that there is a sufficient rate of evaporation. During the daytime, the energy from the sun will guarantee there is sufficient evaporation. But during nighttime and/or when the screens are fully closed, we need to assist the plants to have minimum evaporation. So, how to realize this?
From the research of Wageningen University and Research, it has become clear that minimum evaporation of 10-25 grams/m².hour should be sufficient to support this process. When there is evaporation, water with nutrients is being brought to the different plant parts. Especially immobile elements like calcium (Ca) need to be brought by water flow to the new cells the plant is building.
A lot of disease manifestations can be correlated to deficiencies in Calcium on plant cell level. If you would take leaf tissue samples you could find sufficient Calcium, yet this doesn’t indicate that every plant cell has sufficient Calcium available to be strong enough to resist suboptimal climate conditions or pests and diseases. A lot of times the cause of this deficiency on the plant level can be related to periods in time that evaporation has been stifled for a short period during the nighttime with or without too high root pressure.
The best way to make sure your plants are active 24 hours a day is to provide them with a form of energy. This can be done by a form of radiation exchange or convective exchange. The most economical way is by the convective exchange during nighttime, by means of maintaining some air circulation in the greenhouse. This process can be supported by having some vertical or horizontal fans in your greenhouse. A subtle air movement rate of approx. 2-5 cm/s is already sufficient to deliver the desired result.
When the temperature is high enough in the greenhouse, the exhaust of humidity by venting can also help this process. Stimulating evaporation by using heating should be used as a last resort to grow crops in a more sustainable way.