How does someone become an expert on Gardening, get certified and make it a career?

I am interested in turning my small time hobby of gardening into a bit of a career. Are there classes, certifications, training that I can take in order to become an expert on plants, trees, etc? I’d like to have a deep knowledge of the various kinds of trees, shrubs, flowers that work in different climates, how to best plant and maintain them, to design landscapes with a variety of well-coordinated plants, etc. Should I try to become a certified arborist? Where do I start exploring this potential new career direction? Thanks.