In this work, we propose a characterization of the dielectric properties of olive tree trunk and branches in a nondestructive way, by using a custom-designed open-ended coaxial probe. This research represents a first step in filling a knowledge gap due to the lack of dielectric characterization of similar structures. In particular, by dynamically observing the variation of the dielectric properties, the hydration status as well as other tree pathologies may be detected in the early stages, improving the plant productivity. The main advantage of the introduced methodology is the capability to detect permittivity and conductivity in a wider frequency band; furthermore, the small probe aperture diameter allows to accurately measure water content even in the smaller diameter branches. We measured the living olive plant dielectric properties for 5 days consecutively, in a controlled environment. A substantial difference was found between the more peripherical branches and the trunk, allegedly due to a different water content.