The popular Butterfly Bush, Buddleja davidii, has proven to be a weed. Found growing in natural areas far from any garden, Buddleja’s seeds are dispersed by the wind. Oregon and Washington both list it as a noxious weed.
What is a butterfly loving gardener to do? Try Blue Mist shrub (Caryopteris x clandonensis ‘Black Knight’ ) as a blue/purple, summer flowing shrub substitute or at least only grow the named Buddleja cultivars or the species Buddleja globosa which may be less of a threat.