We present a novel and high-sensitivity Lab-on-Fiber self-heating platform for accurate soil moisture monitoring. It is implemented by combining, within a conventional metallic needle, a standard fiber Bragg grating – working as temperature sensor- and a heating component realized by splicing two monomode fibers with a core offset. The sensor was extensively characterized in the range from 9 to 36%VWC and between 5 ℃ and 40 ℃, providing extremely stable, fast and robust measurements, and exhibiting performance that are comparable with commercial devices. Moreover, the possibility to adjust the input power based on the specific application renders the developed sensor highly adaptable for deployment in extensive areas, offering significant advantages in terms of efficiency, cost reduction and simplicity.