Is butterfly bush invasive?

The Buddleja genus originated in central China and migrated across Asia and to the Americas, evolving into over 140 species as it spread. B. davidii, the most commonly cultivated species in our region, is a native of China.   

Buddleia davidii, produces copious seedlings and is invasive in certain parts of the country, particularly the Northeast and the Pacific Northwest. (See below map).  They don't spread in Iowa as far as I know.  (More info: https://www.brandywine.org/conservancy/blog/invasive-species-spotlight-truth-about-butterfly-bush 

There have been recent introductions to the garden markets of purportedly non-invasive or "sterile" Butterfly Bush. These plants have been bred to not set as much seed. If you simply must have a Butterfly Bush, these varieties may be an option. So if you want to plant butterfly bush - plant the non-invasive ones, just in case.
(Read more here: https://mgnv.org/mg-in-the-garden/are-butterfly-bush-cultivars-labeled-as-sterile-environmentally-safer/ )

Keep in mind - history is replete with plants touted as non-invasive that turned out to be just the opposite (case in point: multiflora rose). Eco-conscious gardeners would do better to opt for the native shrubs. 

Plant native shrubs instead including Sweet Pepperbush, also called Summersweet (Clethra alnifolia). For wetter soils, try Buttonbush (Cephalanthis occidentalis) or New Jersey Tea (Ceanothus americanus). 

You can also plant drifts of tall native perennials. Favorites of butterflies include Blazing Star (Liatris); Purple Coneflower (Echinacea purpurea); Giant Hyssop (Agastache); Joe-Pye Weed (Eutrochium) species and Milkweed (Asclepias) species.

If you already have Butterfly Bush as a planting, and do not want to remove it, you should prevent the spread out of your garden by REMOVING old flowerheads in the fall prior to seed dispersal. Do not dump clippings or flowerheads in natural areas or compost piles.  

Areas where Buddleia davidii is INVASIVE.