In the United States, more than 80 million households participate in some type of gardening activity, including lawn care, vegetable gardening, and flower gardening. This considerable interest in gardening has led to the demand for accurate information about horticultural topics, trends, and research. One credible source for this information is the Extension Master Gardener (MG) Program, of which volunteering is a foundational component. Descriptive characteristics of Purdue Master Gardener (PMG) and PMG interns, characteristics of program participation, and volunteer behaviors were measured through an online survey questionnaire. Demographics, attitudes, self-efficacy, participation in the PMG program, and prior volunteering experience were measured and relationships between predictive variables and total volunteer hours were explored. Overall, the data revealed participants (N = 673) had strong positive attitudes about volunteering. Participants also reported having increased self-efficacy through participation in the MG program, and attitudes and self-efficacy were highly correlated. Based on the results and theoretical framework, a model was developed that can be used to predict volunteering behaviors within MG programs. The predictive model for volunteering behavior revealed that the number of years as an MG and the participant’s level of self-efficacy were good predictors of the total number of volunteer hours.