A tall order, to be sure. You may have to choose which of those qualities is most essential. Ligustrum japonicum (privet) is in the running, to be sure. If erosion control is your top priority, however, there may be other choices you would prefer.

Kay

This post was edited by onederw on Sat, Mar 23, 13 at 7:58

Junipers grow very large and do fine in shade. We have a jungle of them under a grove of pines.

The previous owner had a thing for them, and I much prefer anything BUT them!

They do have the qualities you seek.

Suzi

I should have been more specific. I'm doing a border between me and my neighbor which is on a 3-4ft slope, so the screen I would need should be 6-8ft, as I also wanna keep some light. This may be unusual, but I was thinking that once a strong root system was in place, I could add more soil to flatten out the slope. I was thinking possibly upright rosemary, Phormium Tenax, or ceanothus.

Ceanothus was my first thought, but they do need some sun to grow.

Keep in mind roots grow at a depth "right" for them--if you add more soil on top (is that what you meant about adding more soil?) the roots will all of a sudden be getting less oxygen and might die as a result. (Roots need oxygen as much as they need water).

You are better off terracing the slope by making short walls of concrete blocks or pieces of recycled concrete or stones rather than counting on root systems to flatten your slope for you. Do it right the first time and be done with it.

Ligustrum will be your most reliable and quickest choice, if a quick screen is your priority. I planted a new screen from one gallons late last summer and they're nearing 5' tall already and filling in quickly.