Sit down and prepare a prospectus that outlines  what you intend to research/ write about.  Your prospectus should  introduce your basic working thesis, the research you intend to pursue,  and the basic outline of how you plan to present it.  You should already  be coming to some conclusions about “what a garden is” & “why we  garden” so that you will have something specific to explore.

You are not bound to your prospectus.  You are allowed to change  your mind. However, if you do change your mind / direction  significantly, please submit a new prospectus for my approval. 
Your prospectus must be more specific than, “I plan to do research and find out why people garden and what a garden is.”

I am looking for the specific direction and an outline of at least several things you wish to research.