Agricultural systems are complex and can be used as examples to teach science, technology, engineering, and math (STEM) concepts. However, inclusion of agriculture in core STEM courses is often limited. Three professional development sessions for K-12 teachers were offered in 2021-2022 (hybrid or remote sessions) and repeated in 2022-2023 (in-person sessions) to highlight ways that agricultural plant production systems could be incorporated into core courses like biology, environmental science, chemistry, and math. Teacher participants asked how knowledge level and confidence were influencing their inclusion of agriculture into STEM courses before and after the sessions, and gains in knowledge on content-based questions were also evaluated. Response rates in Year 1 ranged from 8.0% to 38.5%, and usable response rates in Year 2 ranged from 47% to 68%. The availability of lessons or activities and teacher content knowledge both increased teacher likelihood to incorporate in three sessions. However, the additional time needed to incorporate new lessons was identified as affecting the likelihood to incorporate materials after the Year 1 ecology session. Teacher confidence to incorporate agricultural lessons or activities into their courses increased in four of the sessions, though teachers became more aware that limited resources are available to help increase adoption. Awareness of how agriculture can be used to meet learning standards also improved teacher confidence in four sessions. Average score on knowledge-based questions increased in all six sessions, but was only significant for two sessions. These sessions were successful at increasing teacher knowledge and confidence to incorporate agriculture into STEM courses.