Some of you guys have made experience by doing things you had not done before, but were not way over your head. Each time you gained more to apply to the next more involved job. A lot of this stuff is pretty basic. If you have been trimming shrubs and maintaining gardens for ten years I would think you know what they are, how fast they grow, which do well, and under what conditions they do best.
You can look up hardiness zones in books all day long, but some plants have very unique problems in certain regions and don't in others. You won't get that in a book.
On the other hand, the more you can learn from books, teachers, and others that you can combine with practical experience, the better off you'll be. That works whether you have the experience up front or the education up front.