This is a photo series showing the results of a ground layer we did on a crepe myrtle. The myrtle had a major flaw on the back side of the trunk/nebari. The tree was in the pot you see in the first picture. A ring was made in the usual fashion at the level for the new roots. Root hormone. Pack on some sphagnum. Then a fence was built around the tree and that was filled in with soil. We use the same mesh that is used to cover drain holes to build the fences for ground layers. This first picture shows the new roots after the fence has been removed and the soil cleared away.
With the tree removed from the pot, you can clearly see the layer of new roots above the layer of original roots that were contained in the pot.
And here's the tree with the roots pruned, ready for a new pot.