Climate change is intensifying extreme heat, prompting cities to deploy environmental sensor networks to capture hyperlocal conditions. However, top-down deployments that produce data without public input often fail to align with community needs. This paper presents a participatory design study of a high-density environmental sensor network co-developed with a volunteer-run community orchard as part of a city-wide system for heat resilience. Through two participatory design workshops, orchard volunteers acted as co-designers by collaboratively defining the network’s purpose, selecting sensor locations, and identifying key environmental data outputs. The workshops functioned as sites of infrastructuring—building relationships, technical literacy, and shared understanding—while situating environmental data within the orchard’s place-based practices of stewardship. From this process, we derive design criteria for community-driven sensor networks that prioritize both technical function and public formation. These contributions extend participatory design approaches in HCI and offer guidance for future deployments of environmental sensing technologies in community and urban agriculture contexts.