First post, I hope I'm putting this in the right place.

I have a planter on my side yard that has a slightly sloping grade. See attached pic. I just removed a huge birds of paradise from one end and I'm going to build a wooden retaining wall/planter box the length of the cinder block planter so I can level the soil and grow some plants.

My question is, once the planter box is built and the soil is level, will I need to add a drainage pipe? I was thinking of adding one at the base of the new planter wall.

Thanks

Robert