There’s comfrey under the MacIntosh tree and it’s the tallest I’ve ever seen it, but still under 3’ as it’s a dwarf variety. The stuff in the Big garden is the standard stuff, I’ve forgotten the variety. That is known to be invasive. Comfrey is a dynamic accumulator, meaning it mines minerals, etc from way down in the subsoil, bringing them up nearer the surface where other plants can utilize them. It’s often planted in orchards for this reason and why I’ve put it near the tree rows.