This thesis presents a novel method for non-destructive plant health monitoring using ultrasound to detect acoustic radial resonance modes in plant stems. By transmitting ultrasound through the stem and analysing the resulting frequency spectrum, structural and physiological changes can be inferred. Analytical models and finite element simulations (COMSOL) were used to predict resonance behavi0uor, and a custom-built measurement setup was developed to test both plant-proxies and live cucumber stems. Experimental results show that radial mode frequencies shift consistently as the plant dries, supporting the hypothesis that acoustic resonance contains measurable signatures of hydration state. The method proved sensitive to stem geometry, internal structure, and material properties. The study demonstrates the feasibility of acoustic resonance as a tool for plant health assessment. Focusing on the radial mode offers a simplified yet informative signal compared to more complex acoustic approaches. Future work should aim to improve the hardware, automate spectral analysis, and validate the method across different species and growing conditions, paving the way for practical in situ monitoring applications in agriculture.