Cool pics, thanks!
I use a similar method to bury my agaves so they can be assured of great drainage and are easier to remove (hopefully) in the winter. This is the first year I've tried something like this.
I dig the hole wider and about 3-4" deeper than needed, then line the bottom excess space with Alabama sunset-sized rocks. Put the pot in then fill the side gaps with the rocks, then mulch with rocks. When done, you can't even tell they are in pots.
I guess I could try something similar with semps.
