Yes, Butterfly Bush (Buddleia spp) is an invasive plant. Oregon has even banned the sale of this plant. I’ve seen it in action myself as it is blocking out fragile dune vegetation on the beaches in Cape May, NJ. I’ve also seen it taking over an entire streambank for miles along a stream in the Poconos of Pennsylvania.
In order to prevent Butterfly Bush from escaping out of your garden and into the nearby natural areas, you really need to dead head every bloom, and never let it go to seed. This can be almost a full time job because as you’ve probably noticed, this plant has TONS of flowers…….
Where is Butterfly Bush invasive you ask? Check out this map. It’s considered invasive in each of the green shaded states. If you’re not in one of these states, I’d still exercise a huge amount of caution, because it may be only a matter of time.
Rosemary at Toronto Gardens has written an excellent post covering some great native alternatives to the invasive Butterfly Bush.