Chirp is a great little soil moisture sensor. This is a library for the Chirp soil moisture sensor. It supports reading Capacitance (soil moisture) and soil temperature. You can get Chirp on Tindie https://www.tindie.com/products/miceuz/i2c-soil-moisture-sensor/ And read documentation on github https://www.tindie.com/products/miceuz/i2c-soil-moisture-sensor/