As a step toward sustainable wireless sensing, we present a proof of concept system that uses a Plant Microbial Fuel Cells (PMFC) as a power source. To match the very low power production capabilities of the PMFC, we couple it with an ultra-low power wake-up receiver used as a trigger for sampling and transmission of the sensed value. We demonstrate that this combination, with a new, receiver initiated MAC-level communication protocol, results in a sustainable system for reasonable data rates, shown to be 30s in our laboratory setting. This work offers the first steps toward large-scale wireless sensor networks in applications where the sensors are surrounded by living plants that can provide a green and perpetual power supply.