Accurate assessment of plant health conditions across thousands of crops is a challenging undertaking in high density indoor farming as the environmental conditions experienced by individual plants can be very different. Manually inspecting visible symptoms of plant diseases is also not a feasible method because the process is time-consuming and human evaluations are subjective. Compared with traditional bulky sensors, nanosensor-based array can be seamlessly attached onto the plants to identify the onset and type of stress in-vivo via the detection of the plant signaling molecules triggered by plant stress. Most review articles about nanosensors are focused on the working mechanisms, fabrication processes, and device architectures. This review aims at highlighting how nanotechnology can introduce additional value to sensing applications for precision farming, together with the adoption of nanosensors in the current agricultural sector. Further efforts in understanding the applications of nanosensors in a safe and sustainable agricultural environment is also addressed.