More examples of how I look at graphics to think/create/decide visually. For you designers on the less-experienced side-do not be afraid to go through a lot of "trash" to get you to where your design needs to get to.
Overlay, on top of overlay, on top of overlay-work those lines. Work to create that magic. Look at the interplay of elements in the space -- it's about spatial relationships. You will also notice there is very little mention of specific plant material/names. That's for detail time - right now is for evergreen/deciduous/tall/short/weeping/upright, etc. The details will come after spatial relationship is decided.
One other thing about this design process-do not be afraid to jot notes down along with the graphic thoughts. In classes that I have taught what I see a lot of beginners do is work with lines (timidly), or they come in off a site, lots of notes-but then stare at the paper . . . DRAW!!! It won't bite back.