The Cotula groundcover would easily overgrow the tobi-ishi step stones. It may take a while before the path has disappeared but far before that point the characteristic beauty will have gone.
The first photo shows the path as we like to see it after the edges where just cut.
This is an activity without a fixed schedule or frequency. This is done when deemed necessary and when time and weather conditions permit.
Due to the growd of the groundcover the soil gets pushed up and ends up higher or even on top of the flagstones. We use a concrete roll to push the soil back so as to lower the groundlevel around the edges.