USDA map showing where Buddleia is invasive
If it stayed in the gardens where it is planted, butterfly bush might be an asset to the pollinator garden. But unfortunately it does not. Its dust-like seeds are easily carried from our yards by the wind and are deposited along roadsides, in hedgerows, fields and along trails. Because butterfly bush is originally from Asia, it has no natural predators here. Not one native caterpillar is able to feed on it, so it can easily out compete native asters and milkweeds that our local butterfly larvae depend on.
Over the years I have watched butterfly bush spread from roadsides along Rt. 83 to ditches behind a local mall, to open areas along our popular rail trail. Because of the popularity of this plant, its spread into our natural areas is accelerating.
Be careful of the argument that a plant is not yet invasive in your area. Plants have to reach a certain population density before they tip over the edge. So for many less populated places it is simply a matter of time. And our changing climate is making it possible for plants to spread into different hardiness zones.
Another compelling argument for not planting butterfly bush is that by choosing it instead of a plant that helps support the insect and caterpillar population, you are not helping the food web. To survive, butterflies desperately need host plants with leaves that are palatable to their offspring, young caterpillars.
In our own 0.4 acre, we want to pack in as many beneficial plants as possible. So instead of butterfly bush we have chosen important host plants such as oak trees, pawpaws, spicebush, milkweeds, asters, goldenrods and others. These plants are not only host plants, but also provide the nectar that adult butterflies need.