Because of rapid urbanization, urban agriculture’s capacity to reduce the risks associated with natural disasters has been receiving broad attention. Asian megacities have long been exposed to a high risk of earthquakes, but these cities’ vernacular landscapes—characterized by intricately mixed urban and rural land uses—also have the potential to provide open spaces across cities that can be used to mitigate harmful consequences if they are properly managed and conserved. Some cities in Japan’s metropolitan regions have introduced a voluntary program under which existing farmland can be registered and, once designated, used for purposes of risk reduction and post-disaster recovery. To our knowledge, however, only a few studies have attempted to explore this institution, even though such information would greatly benefit other Asian megacities exposed to earthquake risks. The primary objective of this study was to address the following research questions: (1) What institutional arrangements has the government developed to secure farmland? (2) how is registered farmland managed and conserved? (3) what conditions have facilitated landowners’ registration of farmland? Data were obtained through semi-structured interviews with government officials responsible for the program in the six municipalities that offer the program in the Chukyo and Kinki metropolitan areas. Our analysis revealed that the voluntary programs were often designed to work in conjunction with existing land use zoning and building regulations to ensure that the minimum land areas and road connections essential for post-disaster restoration were secured. We also found that the total registered area was in continual decline because of urban farmland conversions where the registration program was not aligned with land use zoning. Finally, this research confirmed that subsidies, when coupled with direct requests from government officials, fostered landowners’ participation in the program and increased the area registered.