It won't spread by runners like V. odorata does when planted in open ground. It usually behaves as a short-lived perennial, and keeps itself going by self-sowing. But even by seed, it won't become nearly as invasive as V. odorata. I would be interested to know how well it would do outside in Idaho - significantly chiilier in winter than many places folks grow it, but not colder than in its native haunts. Maybe you'll be able to tell us in due course...