building a raised flower bed in response to poor drainage
I am new here and have spent the last half hour looking for help with this issue. I have found some help but not specific to my problem.
I have a 170' long flower bed that runs along the back edge of our backyard. This flower bed is sitting directly in front of a 7' tall retaining wall(concrete covered in stucco) that is holding back the hillside that slopes downward into our yard. There is a drainpipe along the back of the concrete retaining wall, but nothing in front of it.
My plan three years ago when we built this house was to plant several shrubs and flowering plants to disguise this wall but everything we planted has died (actually, it has drowned). The soil is solid clay and the yard is totally flat with no place for any water to drain. (picture a courtyard type backyard) Currently, the view from the back of my house looks like a prison yard.
So, I think my only answer is to build raised beds. My plan is to dig down about 8" in the current bed and lay gravel back to ground level, then build the beds 24" high. Do you think this will work? Would 24" be high enough for the root systems of azaleas and other shrubs like japonica?
Also, should I put a drainpipe in the bed on top of the gravel? And if so, shouldn't it be at a slight slope? At 170' I don't know if I can achieve that.
I would LOVE to get any ideas from you on ways to fix this. I live in a small town and landscape designers are nonexistent.
Then, there is the small problem of what to build the beds out of...
Thank you SO much