The Adafruit STEMMA Soil moisture sensor is a durable capacitive moisture sensor compatible with just about any microcontroller / single board computer. Most low cost soil sensors are resistive style, where there’s two prongs and the sensor measures the conductivity between the two. These work OK at first, but eventually start to oxidize because of the exposed metal and have to be re-calibrated over time. This capacitive sensor is far superior as they work far better in loose soil, don’t introduce DC current into your plants, and don’t have any exposed metal to corrode.

The sensor is actually an ATSAMD10 microcontroller with built in capacitive touch sensing. It acts as an I2C sensor and will return a value ranging from about 200 (very dry) to 2000 (very wet). As a bonus, Adafruit also provides the ambient temperature from the internal temperature sensor on the microcontroller, it’s not high precision, maybe good to + or – 2 degrees Celsius.

These can be easily connected to our Raspberry Pi Irrigation and Raspberry Pi Weather board using the I2C header!

Please note: This is just the sensor, you’ll also need a JST 4-PH cable cable to go along for plugging it in!