Oh awesome!! Welcome, @srinivasan! Sounds like a great endeavor! I think you could find some inspiration and research backing in our podcast on nature based therapy:
https://club.otpotential.com/t/17-nature-based-ot-with-laura-park-figueroa-ce-course/783
We haven’t covered any specific articles on designing a sensory garden at an autism center, but I did just find this interesting article: https://www.elsforautism.org/wp-content/uploads/2019/11/Designing-an-Impactful-Sensory-Garden-for-Children-and-Youth-with-Autism-Spectrum-Disorder.pdf