Mangrove replanting, seen in episode 2 of this series, is the most common but also the most controversial method. Indeed, many projects have had disappointing results due to a lack of upstream planning. Faced with this observation, the approach studied in this episode is gaining momentum: so-called “passive” spontaneous colonisation, which is based on the study and management of the hydrological dynamics of the land in order to accompany the spontaneous vegetation. We will discuss the implementation of this approach and its success factors.