I grow red currant and jostaberries under my walnuts. As weeds i have sorrel, stinging-nettle and cow parsnip ( and grasses ) growing under the canopy.
I have not found plants of the lamiaceae family under the trees. I presume the canopy shades too much for the sun loving lamiaceae. I have dead nettle growing between trees but not under.
But i will try the Agastache.