Mg alloys are promising materials for implants due to their biodegradability which can allow the gradual substitution of the implant with new bone. On the other hand, their degradation rate is actually too rapid to match bone regeneration, reducing their clinical application. Moreover, inflammation, pH rise and hydrogen development are often associated with Mg alloy degradation, representing a further obstacle. The aim of this research is the development of natural coatings able to tailor the degradation rate of AZ91 Mg alloy. Polyphenol-based coatings can also add anti-inflammatory and pro-osteogenic properties to the implant. AZ91 Mg alloy was considered as substrate in the form of plane samples or 3D porous structures (by a combination of 3D printing and investment casting). Aqueous solutions of tannic acid (TA) or green tea polyphenols (TPH) were used for the obtainment of natural organic coatings. The combination of the PEO (Plasma Electrolytic Oxidation) of the AZ91 substrate and subsequent polyphenol coating was also considered. The process was optimized to maximize coating homogeneity and absence of cracks. Soaking is a simple and suitable strategy for the treatment of various samples, including complex porous structures, thus assuring homogeneity. Continuous thin coatings were obtained with TA, but the presence of small (micrometric) cracks was evidenced on these surfaces. TPH coatings resulted in thicker layer, with a globular morphology and free of cracks. In static degradation studies (PBS soaking) pH and degradation control were reached more effectively for tannic acid coatings, compared to the TPH ones. On the other hand, TPH coatings resulted in more effective corrosion protection in electrochemical tests. Preliminary investigations showed the possibility of obtaining uniform thin TPH coating on PEO-coated AZ91 samples able to control pH rise and degradation in PBS. Tannic acid and Tea Polyphenols were successfully employed for the obtainment of natural organic coatings for degradation control in AZ91 Mg alloy for orthopedic applications.