I am taking a good course that I found on-line. Check out
www.landscape-designer.co.nz
It is very comprehensive and well-written, by Anna Gresham APLD, a woman from New Zealand. It is a diploma course comparable to, or better than, 2-year courses at community colleges. The good thing is that I have been able to work almost full-time, single-parent a teenager, and move across the country while enrolled in the course. Not that it is easy; it requires hours of detailed work, and an investment in professional drafting equipment.
The book referred to earlier is called Landscape Graphics, by Grant W Reid. It is excellent for drafting and knowing common symbols used in designs, presentation drawings, etc.
You can e-mail me if you have questions. Good luck!