trellis

I would offer it up and mark it where you want to drill some holes. Once drilled use a raw plug and then screw some screws in but not all the way.
Using some garden wire wrap it around the protruding screw heads and then offer up the trellis again. Tie the wire to the trellis.
This will allow you to lower or drop the trellis if you need to paint the wall in the future etc....

also drill the cross members and put them to the wall rather than the uprights.plants need to grow and be helped up the outside of the trellis.not behind it betwen the wall and the trellis