The purpose of this grounded theory study was to conceptualize the pedagogical content knowledge (PCK) of experienced agriculture teachers in the plant sciences. The overarching theme that emerged during data collection and analysis was the influence of beliefs on participants' PCK. This finding guided subsequent data collection and analysis that focused on what was shaping the participants' PCK in plant sciences. The integrated beliefs system was the driving force in shaping the participants' PCK and the primary component of this system was the participants' beliefs about the purpose of agricultural education. These individual purposes for agricultural education included: career preparation, college preparation, practical life skills, agricultural literacy, and student individualization. These purposes influenced the type of experiences teachers sought out to develop new knowledge and how they transferred that knowledge in the classroom. These findings support further examination of how beliefs about the purpose of agricultural education are influencing teacher knowledge and practice.