I like the poplar erecta or there is a narrow, tall variety of service berry that would be great at blocking out the neighbor in the back. Then I would put a rounder shorter variety of crabapple, elderberry, etc., to block out the other house. Lastly, I would alternate bushes varying in color, texture and size, with flowering clematis or climbing roses to fill in the gaps. Climbing roses and vegetables are nice if the owner is into minimal work. I like the idea of creating a green fence out of fruit trees that grow flat against a wall or fence. I am planting a green fence around my backyard this year. There are so many options depending on what the owner wants to put into it and get out of it.
