I like the "box" idea and also "terracing the beds". That could be like a series of shallow retaining walls, but retaining good soil raised above grade.
I have a similar area, but very steep. I always wondered how I would keep the downhill "terrace wall" from tipping over. Thanks, Greene, for that answer! Set up the walls as "boxes without bottoms", but include side-braces so that the top of a downhill retaining wall is firmly screwed to the bottom of the next wall higher up the slope. That way the walls won't be able to tip.
Now I'm thinking of setting out a 3-4 step terraced "staircase" with each riser screwed to the riser above it, for stability.
Then probably scrape the bottoms of each 'step' to a less-steep slope so the depth of the root zone doesn't drop to zero in the uphill half of each terrace step.
Then I can wheelbarrow new soil to the top of the slope and throw it downhill into a series of "boxes".
Thanks, Greene!
