I heard about shiso being used in cuisines so I bought a pack of seeds to plant two years ago. The taste and smell wasn't what I expected and I let the plants be. This year volunteers come up in very acidic soil, in the shade of my yew and oak trees mostly, where nothing else would grow. They have their roles in reducing erosion and feeding soil microbes in those spots so it'snot a bad thing to me. It seems that they get competed out where soil is richer with more optimal pH range. I am wondering if places with perilla taking over could indicate something is off balance? In that case, remediation such as liming will bring back more species to keep it in check.