My Azure watering system did work by itself during my vacation, and thanks to Azure recorded data I know a bit more about humidity and watering.
The data history shows an unexpected behavior:

Water has been pumped everyday in the pots without raising the level of humidity, the big bars on september 10th (300) correspond to manual watering. I also noticed that water was spilled under the pots, meaning that it was going through the soil - totally inefficient!! Also the correaltion of Azure data with real world showed that a humidity level of 200 was perfectly suitable for my trees.

Now I'm ready to modify the program and watering plan:
1 - I must be able to control the levels and timings remotely, I added a "parameter" table in Azure
2 - I must make four measures per day because humidity values shown are unstable