The "Iron Butterfly"
, also known as narrow-leaf ironweed, is a species of ironweed native to Oklahoma and Arkansas well suited to the home landscape. You will love it for its late summer/early fall bloom, and your pollinators will be beside themselves with joy.
My previous experience with ironweed was with common ironweed, which sports this comment from Wildflower.org: "Too aggressive for small areas. Needs competition." (!!!)
Narrowleaf ironweed is finely textured and drought tolerant. It's native habitat is in dry, rocky, sandy soils. However, ours is located in moist clay. Amended moist clay, but it's still consistently soggy and, shall we say, "thick." The cultivar "Iron Butterfly," which was introduced by the University of Georgia, is widely available at online nurseries--we got hold of ours locally, and could not be more pleased. At a tour for local Master Gardeners, a couple of folks asked if it were Eastern Amsonia--it is very much like that plant in form and texture--in all but size. Our amsonia is roughly 4'x4'--a much larger presence in the landscape. The more petite ironweed (2'x2') is a better fit in our landscape, frankly.
The first year this perennial is in the ground it may not excel, but hang on for year two. The tightly-wound form is almost shrub-like and about as carefree as you can imagine. Not only will it tolerate and thrive in a variety of moisture levels, it is perfectly happy in full sun or part sun locations. And while the form makes it easy to integrate into smaller landscapes, the massive quantities of delicate red-violet blooms make it a true standout. Pair this with some "Fireworks" goldenrod behind and things could really get explosive!
I would expect narrowleaf ironweed to perform very nicely within a medium to large rain garden. It's more formal shape could be very helpful in maintaining a more "tended" look to what can sometimes be a messy area of the landscape. Rain gardens frequently spend lots of time DRY--and many, many plants selected for rain gardens are also known for their drought tolerance.
Ironweed is a fabulous plant for butterflies, no matter which species in the genus you select. Some other varieties are also deer resistant (Woolly Ironweed, for example--another well-behaved species), making them even better selections for some gardens.