What's the reseeding situation with these where you are? Over here recently selected, supposedly seedless cultivars are most of what I see offered now - due to fertile forms of Buddleja davidii having become such a nuisance. River banks, parking lots, railways, stone building facades...any kind of a stony barren in particular may have numbers of them come up.

They're not invasive in FL. If I lived in PNW, UK, or Mid-Atlantic I would not grow them but they are annihilated here by nematodes haha so there's no threat of them escaping

I also always deadhead mine (which are in pots on a walkway) since I grow them for pollinators and want to maximize the bloom period. I have a variety of native flowers too but most start up later in the season. but i do understand how they are problematic in other areas

The old standard lavender BBushes have the best fragrance -- seems like breeding for different colors has reduced other desirable traits, which seems to happen often.