Use a capacitive soil sensor, or power a resistive probe only during a reading.
What the message means
A resistive probe passes current through the soil, which eats the metal. Readings then drift week by week.
Fix it in this order
- Replace the resistive probe with a capacitive one if you can.
- If you keep it, power the probe from a pin and switch it on only to read.
- Calibrate with dry air and a glass of water to get the two end values.
- Seal the electronics, and keep the connector above the soil.
- Average readings and read a few times a day, not constantly.
- Check the sensor output range against your ADC.
Why it happens
A resistive soil probe passes current through the soil. That current corrodes the metal over time, so the readings drift and the probe fails within weeks or months. A capacitive probe has no exposed metal in contact with the soil and lasts much longer.
Use a capacitive sensor, seal the electronics, and if you keep a resistive one, power it only while taking a reading, for example from a GPIO pin or a transistor.
If you see this, do this
| You see | Do this |
|---|---|
| Reading changes over weeks | Corrosion. |
| Reads the same wet and dry | Wrong calibration or broken probe. |
Related
ADC noise, analog sensor basics.
Last reviewed: November 2026. These are the usual causes and the order that finds them fastest. Test on your own board; clones and cables differ.