Soil Sensor

Hi everyone.
I recently bought from a reseller of DFRobot the “Gravity: Analog Capacitive Soil Moisture Sensor- Corrosion Resistant” and i use it to figure out how mutch moisture is left in my plants.

i track does data in Grafana and they are basicly a line and behave the same even they are in to plants in 100% coco soil.
I bought a seperate power supply to give the sensors a reliable source and i catch the data with a esp 32 wroom 32.

This is my chart: