It is a North American native plant so by definition not invasive. But it does have the ability to seed around rather freely. If you do not wish seedlings popping up here and there, then you need to deadhead quite religiously. Which improves the look of the plant and promotes more blooming anyway.

Great. I placed in a relatively confined area (with edging) and planted a few hundred seeds (came in a 1/4 lb. bag). So we'll see how they do?!

I have always found their reseeding to be charming. I wouldn't call them aggressive at all, and if a few plants show up where you don't want them, they are an easy to remove annual.

Tangential: Like Gardengal, reserve the term "invasive" for actual listed plants rather than "garden pests"." Although, simply being native to North America doesn't automatically make something non-invasive. For example, something that is native to the East Coast can become invasive on the west coast where it isn't native, and vice versa.

Thanks ZachS. I'm hoping it's somewhat invasive, in a good way. We will see?! I planted Jupiter's Beard (red valeriun) too, so hoping for some invasions in some areas...