The urban food garden is an interesting natural solution to the need to develop sponge cities structured and designed to absorb and capture rain water for reducing flooding, worldwide. This study applied a storm water management model and field experiments to investigate properties of the garden substrates. Taipei City was taken as a case study as the Taiwan government has promoted urban food garden projects since 2015. The urban food garden in Taipei has established a cultivable area of 197,168 m², 64,026 m² (32.5%) of which is designated as green-roof gardens and the rest as domestic gardens. Four substrate mixtures were found to have infiltration rates positively related to their soil water content. Substrate 1 had the highest infiltration rate (6.47 × 10⁻⁵ m/s) and soil water content (281%) when vegetation grows in limited containers. In 2019, the total water retention capacity of the urban food garden in Taipei City was 50,550.7 m³. This means that 1 m² of the urban food garden in Taipei retained 256.4 kg of water. Considering climatic conditions, the water retention capacity of the green-roof gardens in Taipei ranges from 28.2% to 41.0%. During short-term high-density rainfall events, the green-roof gardens were found to be more efficient in reducing the runoff volume, whereas during long-term high-density rainfall events, they were found to be more efficient in reducing the runoff peak flow duration (~20 mins) compared with concrete surfaces. This study proved that establishing the urban food garden contributes to increasing the water retention capacity and reducing the volume of surface runoff and the duration of runoff peak flow in prevention of flood disasters.