There are several characteristics of working in an urban environment that challenge the usual forms of work prescription. This is a case study on the work of gardeners in an urban setting in the north of Paris. This paper develops the notion of territory, which we define as a system that is locally rooted in an open environment through the situated actions of gardeners' work. As the employees do their work in an outside environment, interactions in real-life situations are beyond the control of work organization. City gardeners' work is carried out in a green, living and human environment. We conducted detailed open observations in a town's green zones. These were complemented by individual interviews in work situations and by collective interviews within the boundaries of the municipality. We use the notion of territory to highlight the particularity of work within organizations where the work environment cannot be limited to the space inside their walls. The gardeners' work makes it possible to link residents and passers-by (on foot or in vehicles) with the town's green spaces (micro-ecosystems). Their work consists in connecting the different expectations and needs of the various life forms: the human beings (with a variety of lifestyles), as well as the plants, insects and animals. The particularities of working in an open environment create complex forms of prescription. The notion of territory, rarely used in ergonomics, proves to be fruitful for considering work in these contexts.