An optoelectronic device for measuring the water content in a plant element and an apparatus designed to evaluate and monitor in real time the state of hydration of the plant covers. The device includes an optoelectronic probe connected to a measurement module, the probe including: i) a first light source emitting at a wavelength corresponding to a strong water absorption band; ii) optionally, a second light source emitting at a wavelength close to the first source and weakly absorbed by water; and iii) a photo receiver having a spectral response that corresponds to the emission bands of the first light source or of the first and second light sources, the device including elements for modulating the average optical power emitted by the light source or sources at a defined frequency, and elements for synchronously detecting the light received by the photoreceiver.