Plants present a versatile engineering platform to design sustainable and multifunctional materials due, in part, to their natural abundance, self-growing capacity, and functional diversity. While plant-based materials technology has started to gain momentum in photonics, robotics, and soft electronics, it has not yet met phononic materials design. In this work, we investigate the phononic behavior of micro-structured plant cells scaffolds composed of dehydrated plant cell walls. Using laser-generated acoustic waves, we measure the dispersion curves of sub-GHz surface and guided waves in these biocomposites, and reveal the presence of phononic band gaps due to their interaction with compressional and flexural local resonances of the cell wall structure. Moreover, we show that these locally resonant phononic features can be controlled by altering the phenotype of the plant cells. Our results suggest a significant potential for acoustic manipulation of MHz-GHz frequencies using bio-derived surfaces, which we anticipate can lead to a wide range of green ultrasonic devices with tailorable properties.