Few studies in urban forestry have examined the motivations of urban forestry volunteers. In this research, two social psychological theories (Volunteer Functions Inventory and Volunteer Process Model) are utilized to examine motivations for participating in tree planting activities. The Volunteer Functions Inventory can be used to examine the needs, goals and motivations that individuals seek to fulfill through volunteerism. The Volunteer Process Model sheds light on the antecedents, experiences and consequences of volunteerism at multiple levels (individual, interpersonal, organizational, societal). An understanding of volunteer motivations can aid practitioners in the development and implementation of participatory urban forestry programs that are attractive to stakeholders. We conducted a survey of volunteers who participated in a MillionTreesNYC volunteer planting event and a focus group of urban forestry practitioners. Survey results reveal that volunteers have varied motivations and a limited knowledge of the community level impacts of trees. Results from the focus group reveal that providing education about the benefits of trees and maintaining long-term communication with volunteers are frequently used strategies for engagement. However, the public’s lack of knowledge about urban forestry and an inability to connect to audiences are practitioner-identified challenges for recruiting stakeholders to participate in their programs.