Footing required for a low garden wall?
How fast would you like it to crack?
Drystack walls without mortared joints are somewhat tolerant of frost movement. Many landscaping wall block systems intended to perform that wall function are out there, as well as actual drystone walls from natural stone.
Mortared joints will break unless sitting on a solid foundation that does not move.
That does not need to be solid concrete, there are other foundation systems such as the &quot;rubble trench&quot; that Frank Lloyd Wright (somewhat) popularized (also seen under virtually every railroad track) - that does require good drainage so that the rubble drains, rather than being full of water.