Research experiences for undergraduate (REU) students are valuable for exploring STEM professions. Students from underrepresented groups and non-research institutions may not have the opportunities to engage in hands-on research. A primary goal of our Applied Plant Systems REU was to provide authentic research experiences for students who may not have the chance. Mentoring is key to the success of a REU, yet intentional mentoring is not often prioritized. Over three summers, we explored student perception of the value of mentoring within an agricultural STEM REU. Pre- and post-survey responses were analyzed, and we found that the students valued specific aspects of mentoring during their REU. Interestingly, at the end of the REU, the survey result showed that the students placed a higher importance on items such as mentoring being a systematic process and that mentoring is based on friendship. There is clear indication that students know good mentoring when they experience it, even if it is not verbalized. Based on the survey responses and comments from students involved in this REU, we developed practical mentoring items which can be incorporated into research programs to enhance the mentoring experience.