Ok this is meant to be cheap and easy. It is not meant to be an engineered wall, nor a wall that a city or agency is going to inspect. It's meant to be a rural garden wall. Our dirt is decomposed granite and in pockets it has gravel, sand and a little loam. We discovered that someone used it as mortar on a wall in the 1930's and the wall was still up. I was using some concrete mix from the local quarry and it made awful concrete, no finish and it cracked easily. I figured this out and tried out dirt, great concrete!
Not something I'd build a structural foundation out of, but for garden purposes it's good for at least 50 years. Some of the walks and walls we built 30 years ago still look new.
A cheap farm wall with a really cheap sill plate made out of treated wood with some deck screws in it and pressed into the wet concrete. Hokey is good. If the wall is built exactly, people notice your mistakes. Make it look rural and it will look quaint. If it falls over, with steel in it, life really sucks.