Building Decorative Cob Walls in Ohio

Hello,

I am embarking on a project with several high school students to build a multi-use community garden. The kids are very excited about building broken pottery mosaic walls...I want to use cob as the base material. These will be free standing walls encircling an edible water garden and stage, with edible vine plants growing on the back of them.

I have a few concerns in that I am a newbie mostly learning from the internet.

1. Should I be concerned about water damage (considering we have no roof)? How can I prevent water damage?

2. I am hoping to plant things at the base of the walls...should I use a different material for the base?

I appreciate any advice you can give or resources you can point me to

Howdy Alex, welcome to permies!  I have never built with cob but would like to build some garden walls myself someday.
In doing research on line it looks like many folks build their walls on top of a rubble trench foundation. Maybe you could find someone who is trying to get rid of some old concrete or "urbanite" ?
I am also seeing, and love the look of, the wooden "roofs" that people cover the walls with. I am not sure if this is necessary to protect the wall but it sure looks nice. Maybe find someone getting rid of pallets and break them down and reuse the wood for roofing?

People who have built or observed outdoor cob benches or walls have reported that they always disintegrate within a few years, depending on the climate, even if protected with a layer of plaster or tile. A roof keeping most if not all rain off, as well as a raised foundation of dry-stacked rocks or maybe urbanite (concrete chunks), will be necessary if you want this wall to last. A shingled roof as mentioned might work, but would need lots of overhang and air circulation above the cob in order to be effective.