You can consider that a topic is too broad when you have way too many ideas about that topic or too many things about it that you can talk about. The opposite of too narrow, that leaves you with only one specific thing to be talked over. Farming in the Middle Atlantic States opens a lot for "<em>what states", "why is it different?", "farming what" </em>and so on. Maybe farming in a single state would be more adequate since you will still have many different kinds of farming to talk about in a single state.
