I have a concrete wall too. I read a suggestion I liked using wood lattice. If I can find it again, I will post the picture but I will do my best to explain the concept.

First, you make a frame out of wood. Maybe 1x2 or 2x2 -- whatever you have on hand. Nail or screw the lattice on to this. Set aside.

On the wall, attach two strips of wood (again either 1x2 or 2x2) so that the run up and down on the wall. On one side, attached hinges. Then attach the other part of the hinge to the trellis framework. Basically you have made a trellis "door" on the wall.

Now you need hook and eye hardware. On the other strip, attach the hook part and to the door attach the eye part. The door will stay closed when you want it flat against the wall and have latched the hook and eye together.

You could also arrange it so the lattice door has the hinges on the top or on the bottom, but you'd have to change the strip pieces to run across the wall accordingly. The book had the hinge going across the top -- which I assume is so the door, even if not latched, will hang down closed.

Then you can just grow your things up the lattice, and at the end of the season "open" the doors to fish out plant debris and/or clean or paint the wall.

HTH!
V.