The popular butterfly bush (buddleia ) is deemd invasive in some areas and not others. It all depends on where it is happy.
When I lived in Cleveland , Ohio and Albany, New York, butterfly bushes were popular but pruning them was never an issue. They died back each winter and sprouted anew. The snow cover protected them from the worst of the cold temperatures, and each spring the old stems were removed and new growth took over. In Indiana the snow and temperatures were slightly milder and common practice was to prune close to the ground. Whatever was above ground when icy winds hit was killed, but some years, in mild winters the whole bush would survive, but it still formed a neater bush when pruned each year. In Pittsburgh, the average winter was warmer still, slightly. The bush frequently was able to set seed which survived to produce new plants each year. Alas many of the seeds viably germinated, making the bush a definate problem. Since moving to Atlanta, I have seen many butterfly bushes in garden both public and private. They do not seem to be creating a problem. The seedlings have a shorter, milder winter and have to to deal with a very long, dry summer. This may be why the bush is not considered quite such a problem. In England this past summer, I noticed that the buses were wild along the railway lines and made a beautiful scene to look at, but no doubt they are troublesome in a well kept garden.
So it would appear that this splendid bush has the potential to be a problem in mild winters and moist summer rather than very cold winters or very dry summers.
