Ever since I bought my first home, I have been free lancing in landscape design. We don't grow up with a knowledge of horticulture and landscape design, so we muddle along making mistakes with our home exteriors. I took a correspondence course in landscape design, and proceeded to sell designs to owners of large and small properties.
Engineers are qualified for landscape design because it involves spacial visualization, construction, drainage, and other disciplines. The key to my work is making design elements work in many ways, not just beautification (screening, framing the view, creating a vista, shading, seasonal color change, winter landscape, etc).
In the Chicago suburbs I sold some nice designs to doctors and land developers. It snowballed into a nice seasonal sideline. Word of mouth really works wonders. It's important to sell the job before you make the walk around and give away ideas.
Currently I am providing quote packages, which help the owners make decisions on contractors for the various elements of the job. The owner probably gets my fee back in competitive savings.
Lfetime Career Schools was based in LA, and it was sold to a company in PA. Contact them on the internet if you are interested in their correspondence course.