Thanks to the integrated Bluetooth function of the Raspberry Pi (a Bluetooth USB dongle is required for older models), certain Bluetooth sensors can now also be integrated. One of them is the “Xiaomi Mi Flora Plant Sensor”, which is available in stores for around 25-30 EUR.
The sensor has 4 interesting values: soil moisture, temperature, brightness and conductivity, the latter being the soil nutrient content.
The project we need for this is here:
https://github.com/ThomDietrich/miflora-mqtt-daemon
In principle you can proceed exactly as in the instructions. In OpenSprinkler you simply set up an MQTT sensor and link it to the topic “miflora/<sensor name>”, where <sensor name> is the name that you entered in the config.ini.

Another note: Bluetooth scanning with “sudo hcitool lescan” didn’t work for me because the hcitool has probably already been discontinued. Instead, “sudo bluetoothctl scan le” should work.