Garden-based teaching plays an important role in bringing the formal and informal learning environments together and is applied at different educational levels. Teachers are expected to use multiple teaching technique in different learning environments align with the contemporary educational approaches. However, educational research shows that teacher education programs still mainly focus on the classrooms and teachers are not prepared or do not feel prepared to take their students out of the classroom. This case study aimed to introduce the educational use of school gardens to the pre-service science teachers and to improve their subject knowledge, the subject teaching competency and provide the confidence of teaching outside the classroom, school garden. The study was conducted in a public university with the participation of 38 pre-service science teachers in the 2014-2015 academic year. Three preservice science teachers prepared the lecture based on the "lesson study" model and gave the lecture to their classmates in an outdoor learning environment (campus garden) enriched with the mobile technology. The preservice teachers stated that they are aware of the importance of using the scientific name of plants, but they do not feel themselves competent. The results show that the lesson study model can contribute to the preservice teachers' subject knowledge and professional competencies. The results of the study are expected to contribute to the preservice science teachers' awareness of the outdoor learning environments, support the practice-based subject teaching and their general professional competencies.