The first thing you should do before starting this garden is ask yourself:

Why am I doing this??

If you don't have a clear answer in your head to that question, now is the time to really evaluate what your motivations are. Think about what this project will demand from you and from your students (not to mention parents, the school administration and other teachers), then consider whether you're up for the challenge. If you are, great!! If you're not sure, maybe this year isn't the year to start this project and it wuld be best to hold off until you're ready.

To get you thinking, here's a short video that explains why Stephen does it: