When we moved into our fixer-upper, the above plants were strewn about the yard in unattractive plastic pots. I lined them up against a wall and stacked cobblestones around them.
It took about an hour. And I have zero masonry skills—my father can vouch for me—so anyone can do this. This one has lasted about two years and hasn’t needed any adjustments.
(One note: I’d avoid making this planter if you have small children. Tiny fingers could get hurt by an unbalanced rock.)
These cobblestones happened to be scattered throughout our yard. (Some buried, some not.) But you can buy similar ones at your local landscape supply store. If you live in the Bay Area, I’ve bought some at Broadmoor and have heard good things about Lyngso.