I have a retaining wall with space behind it and then a straight drop off from higher ground (about 4-5 feet higher than the wall). What can I plant to hide the drop off and the space behind the wall? I can't afford to haul in alot of dirt to fill the space.
You could do an advanced search in our plant encyclopedia for plants in the 4 to 6 foot height range and that would be hardy in your Zone. You can also select for other qualities that might be important such as sun exposure or moisture tolerance.