How to Set Up the DHT11 Humidity Sensor on the Raspberry Pi - Circuit Basics
Build a Raspberry Pi Moisture Sensor to Monitor Your Plants
Amazon.com: ACEIRMC 2set Soil Moisture Sensor, Icstation Humidity Detector, with Corrosion Resistant Probe, Digital Analog Signal Output for Arduino Raspberry Pi Garden Automatic Watering System : Patio, Lawn & Garden
How to read soil moisture level with Raspberry Pi and a YL-69/FC-28 moisture sensor