Yes, I get paid for my work, all of it, but that is what I do. I do design work and consultations for homeowners, HOA's, property managers, manufacturers, site planners and landscape contractors. Design work is billed out by the hour, or a generalization of the time the design will take.
What is your time and ability worth per hour? Don't forget about overhead, payroll, drawing materials, education, books, computers, software, printers, ink, and the place you keep it all. You also have association dues, trade shows, vehicle, digital camera and a host of other expensive tools that you need to design a landscape well. Does $50 an hour cover all that and make you a profit? How long is it going to take, how many trips to the client, how many times will you have to redraw.
Don't forget on-site consultations, that as an additional revenue source.
So yes, you can go to college, earn a degree as a horticulturist with a specialty in landscape design or complete a degree program, internship and take a test, equivalent to the lawyer's bar exam and become a landscape architect and enter the job market. Once you have accomplished that and have the artistic talent and you get good at what you do, you can earn an outstanding living making designs.