I have a deep red Bee Balm at the cottage and its not as fast spreading as the purple but in your climate I don't know how that would go as ours dies down each year to nothing don't think yours would. As for self seeding I have not seen it come up anywhere else than where I have planted it. Hope this helps
A man who looks into a collie's eye to receive an icy stare is but a fool. Be at one with man's best friend and through his eyes you will see his very soul.