[Cob] Foundation depth for garden walls?

[Lynne Miles-Morillo]

How deep does a foundation for a garden/courtyard wall need to be?  Is
it the same as for a house or can it be somewhat shallower?

Background:  I'm a complete novice (but most enthusiastic) builder,
and garden walls cum outdoor fireplace are to be our first project now
that we've done a cob workshop.  We hope someday not too distant to
get going on an actual *house* but think improving our current
property and giving ourselves a bit of practice & experience might not
be a bad way to start.

I searched & searched through the archives and found nothing about
garden wall foundations but a post from Georgie of cobinthepark.ca
(<http://www.deatech.com/pipermail/coblist/2005/009286.html>), which
mentioned a wall in Toronto for which the foundation was only 6"
below the surface of the ground.  Toronto's much cooler than central
Indiana, where we'll be building, so perhaps I don't have to dig quite
so deep for our wall?  (And why would one use landscape fabric?)

Thanks in advance for any & all responses,
Lynne MM in IN