The Iowa Community Tree Steward (ICTS) Program is a volunteer-training extension program based on a premise of "trading" training for volunteer service. This program trains volunteers to care for trees. Following training, volunteers are expected to engage in planting and pruning trees, giving advice to neighbors, and advocating for trees and tree care in their communities. However, volunteer engagement in terms of hours of service is variable, leading to inconsistent results in community tree maintenance. The objectives of this study were to: (i) assess factors affecting Tree Stewards' motivation to contribute volunteer hours, and (ii) examine the relationships between motivational factors and participants' level of activity. A mail-questionnaire was used to query ICTS participants about five motivational factors - values, understanding, personal development, community concern, and esteem enhancement. A majority of respondents strongly agreed with statements related to understanding, followed by values. Respondents did not agree as strongly with statements about personal development, community concern, and esteem enhancement. Respondents' level of agreement with statements related to motivation and advocacy were used in independent regression models to examine their relationships to three measures of volunteer service - number of hours served, number of activities engaged in, and number of types of collateral volunteering. Strong relationships were detected between values and collateral volunteering, between personal development and both number of hours and number of activities and between advocacy and number of hours served. Extension programming can be modified to directly address factors that lead to more consistent and on-going engagement of volunteers.