Joe, I teach a variety of subjects, in a variety of settings. I teach Cultural Geography online for a local junior college. I teach classes on Church history and the history of Christian mission. I also travel abroad and teach seminars for NGO workers about how to work in/with other cultures.
Horticulture is only my hobby, but over the years as a researcher and social scientist I have "learned how to learn" about any topic. I often tell people that knowing how to learn is more important than going to college, however, most people need the discipline of course work and grades to keep them focused enough to really learn.
For example, the internet contains vast information about gardening, but you have to learn to differentiate between reliable information and hearsay. Many universities have ag. extension services that put out great information, based on hard science and field trials, about raising fruits in the home garden. I learned a lot about Raspberry and Blackberry culture from publications produced by the University of Arkansas extension service, and similar publications by a few others like NC state and U of Texas Austin.