If I were doing edging stones set in concrete, I would dig a trench, put down a couple inches of 3/4" clean gravel, then pour a continuous slab with a minimum thickness of 6" and rebar in it, then mortar the edging to the slab and backfill.

Crazy, right? But I see people slapping down an inch or two of mortar or concrete and setting the blocks in that. That does nothing. I'd be amazed if it takes a year (in a climate that gets winters) for that to crack.

What I do for most of my clients is dig a trench, put in several inches of 21A (aka crusher run or 3/4 minus), compact it, put in a little more loose for a bedding layer, set my stones, and backfill. This way it's a flexible installation and can move with frost, etc without cracking. Way better and less expensive

Sounds good. Thank You