The plant water Anomalous Phase sensor can determine moisture levels in plant leaves, stems and wood. The sensors described include several embodiments of the sensor, all of which estimate moisture levels by determining changes in the phase spectrum of an anomalous-phase resonator. Two embodiments include a planar transmitting antenna array with two slightly detuned patch antennas and a detector. In a first embodiment, the detector is a dipole antenna centered and out of plane with the transmitting antenna array. In a second embodiment, the detector is a singular rectangular patch antenna coplanar with the transmitting antenna array. The third embodiment is similar to the second embodiment, but is formed on a flexible substrate, so that the sensor can be wrapped about a twig, branch or other plant structure, in a non-coplanar arrangement. To compensate for temperature affects, a reference sensor may be integrated with an active sensor.