Public gardens in urban areas play an important role in the development of physical and mental health of the people. These spaces are also social spaces, where people meet to interact, exchange, and organize collective activities. They create a unique identity for each residential area in the city, which is a premise for green urban development. In Hanoi, public flower gardens (PFGs) were formed and developed from the French colonial period, mainly those in the historic city centre. Facing the forceful urbanization process and the changing of urban structure, in order to evaluate the role of all public flower gardens in the historic city centre area, we carried out a systematic survey from 2019 to 2022. We surveyed all 30 PFGs in five central districts of Hanoi, and interviewed 229 users at these gardens. We also conducted research on relevant documents regarding the management and planning of green space and water infrastructure in the city. Moreover, we implemented an experimental workshop, combining an urban living lab (ULL) approach and an in situ landscape approach, to develop urban landscape design ideas with community participation. Based on the data from this research, this paper analyzes the potential for the establishment of urban blue-green infrastructure (BGI) from these PFGs and aims to evaluate the role of community participation in landscape design for the city. Data from multiple collection methods provide a multi-faceted understanding of the original characteristics of the PFGs in Hanoi and their importance in urban life. The project results supply experimental lessons from urban landscape design activities through community participation, which opens up the potential for developing sustainable urban spaces based on existing natural structures in the city. The main result proves that active community participation until the end of the research project raises public awareness and ensures the social acceptance of the final design. These lessons allow the improvement of urban landscape design practices and the establishment of BGIs from PFGs in an efficient and sustainable manner for green cities in the future.