I recently visited The Courts garden in Holt, Wiltshire. It’s a beautiful but compact garden and part of it is given over to a small kitchen garden surrounded by box bushes. The garden has a very ‘natural’ feel with most of the pathways blending in with the backdrops. Here they have used natural materials to denote pathways.
The gardener has used branches (maybe prunings from the fruit orchard?) as borders from this small herb bed. They have used thick branches to form the main pathway and smaller, thin branches to mark out the beds. Informal but very effective.