In cities nature is taking on a new role as infrastructure, providing essential services in terms of temperature regulation and water management, as well as the provision of habitat for biodiversity conservation. With this turn to green infrastructure have come new challenges to maintenance. Plants are lively things and if they are to perform their infrastructural roles they must be routinely tended to in particular ways. In the context of neoliberal governance, much of this labor falls to volunteer humans. Framed as stewardship, this volunteerism for plant-city thriving is posited as a way to meet maintenance needs while promoting human health and well-being and creating support for nature-based solutions through a sense of ownership and responsibility. While it is thus possible to read stewardship as an enrollment of people and plants into the reproduction of neoliberal urban political ecologies, in this paper I argue that such an analysis overlooks the involution of plants and people that occurs during acts of stewardship. Drawing on ethnographic research with street tree stewards in New York City I explore how vegetal agency draws people into affective, embodied relations. During acts of stewardship, trees act on people and reconfigure their relations in ways that potentially exceed the strictures of stewardship. Rather than allowing stewardship discourses and critiques thereof to be our sole frame for understanding these people-plant relations, we should also consider them from the perspective of vegetal agency and what human-tree involutions do within, around, and to human practices of stewardship.