The garden area I first planted it is still infested. Manageable, but kind of annoying to keep having to pull it up. Although I actually like the citrusy odor they give off when disturbed. On the other hand, I haven't managed to keep it alive when trying to grow it in a bog-like confined space. And I don't think I've seen it self-seed, just spread by roots. So it's probably fairly safe as long as you've got the roots 100% contained.
