The roles of gardens has expanded from private to public spaces. This study aimed to define the functions of gardens based on their evolving roles and develop evaluation methods for each function. Results comparing thermal environment factors between garden and control plots as well as differences in thermal environment and heat stress indices among garden components, are as follows: Time series data revealed differences in air temperature ranging from 0.8°C to 3.0°C, black globe temperature ranging from 4.4°C, and wet-bulb globe temperature (WBGT) ranging from 1.6°C between garden and control plots. The garden maintained cooler temperatures compared with the control under all conditions. Notably, temperature increases in the garden were more gradual relative to those in the control. Although gardens do not cause large temperature drops, they effectively regulate temperatures over time via their small green spaces. Heat stress indices were also lower in the gardens, indicating an improvement in thermal comfort. Among garden components, wooden structures had higher surface temperatures, whereas shade from greenery helped reduce temperature differences. In terms of outdoor microclimate, buildings and greenery shade provided “moderate” improvements in the UTCI heat stress index. This suggests that although building shade enhances thermal comfort, small green spaces can also improve thermal comfort by planting trees and grasses. By identifying garden components that influence microclimate control, we can guide the selection of garden locations and components with the following priority: buildings → trees → surrounding paving materials → garden paving materials → facilities.