In this paper, we examine the mechanisms of volunteering at tree-planting events conducted as part of a new, multi-organizational tree-planting effort in northwest Indiana called CommuniTree. A broad literature exists on general volunteerism as well as environmental volunteering, urban forestry volunteering, and even tree-planting volunteering. Yet, the motivations, environmental attitudes, and personal efficacy of urban forestry volunteers in particular are not fully understood, nor are the outcomes and implications of volunteer participation in neighborhood greening programs. A 22-question (34 individual items), self-report survey was administered in-person at CommuniTree tree-planting events in 2017 through 2019, obtaining 114 responses. CommuniTree volunteers who responded to our survey are mostly white, male, full-time students of college age (18-24), who came to the tree planting by way of their university professor or a friend or family member telling them about it. Volunteers who completed our survey were motivated by intrinsic factors including a desire to help the community and a desire to help the environment, as well as extrinsic factors such as to complete community service hours, receive school-related extra credit, or as required through their employer’s partnership with CommuniTree. Additionally, volunteers report high rates of pro-environmental behavior, a high-level understanding of environmental issues, and high personal efficacy. Here, we frame our results in terms of the Volunteer Process Model’s three phases of volunteerism, and thereby consider the antecedents or prior conditions, experiences, and consequences or outcomes of volunteering in the context of respondent motivations, attitudes, knowledge, personal efficacy, and self-reported benefits and drawbacks of trees.