Adafruit STEMMA Soil Sensor - I2C Capacitive Moisture Sensor

This sensor use capacitive measurements using only one probe, don't have any exposed metal, and don't introduce any DC currents into your plants. Adafruit use the built in capacitive touch measurement system built into the ATSAMD10 chip, which will give you a reading ranging from about 200 (very dry) to 2000 (very wet). As a bonus, Adafruit also give you the ambient temperature from the internal temperature sensor on the microcontroller, it's not high precision, maybe good to + or - 2 degrees Celsius.

To make it so you can use the sensor with just about any microcontroller, Adafruit have an I2C interface. Connect a 4-pin JST-PH cable to your microcontroller or single board computer to 3-5V power, Ground, I2C SDA and I2C SCL and then run Arduino Micropython of Adafruits CircuitPython code to read the temperature and capacitive measurement.

Note:

This is just the sensor you'll also need a JST 4-PH cable to go along for plugging it in.