Conoclinium coelestinum
Until today, I always thought of ageratum as a low-growing garden annual that you could buy readily in any garden center– but I never knew it was also a native wildflower!
I recently found a colony of these plants growing along the side of a shallow pond in Blacksburg, VA. The plants were tall and distinctly “minty” looking, but they lacked the square stem of the mint family… The bluish-purple flowers screamed AGERATUM, but I thought–no way! But what IS it? I made a note to myself to “look up this wild ageratum” as soon as I got home. Sure enough, I found this very accurate description online:
Blue mist flower, or wild ageratum is a perennial wildflower that can reach up to 3 feet in height. The leaves are opposite, hairy, ovoid, toothed and have short petioles. The blue to purple flowers occur in flat-topped clusters at the top of the stem. The clusters can be several inches across in width. Mist flower plants arise from a dense system of underground rhizomes, so they can be mildly weedy if introduced to the home garden.
Mist flower grows in full sun. The plant prefers WET conditions like those found near shallow ponds and soggy meadows. Bloom time is late summer to early fall.
Well there you have it! The ancestor to our common garden annual is an August-blooming, wetland-loving native wildflower! Wild ageratum is blue mist flower.
Note: I later found wild ageratum growing along the New River in Giles County. The plants formed large “drifts” of color along the river banks in mid-August.
VIRGINIA WILDFLOWERS 
Gloria, Don’t forget Queen Ann’s Lace and blue chickory — two of my favorites that are blooming now.
I have such a backlog of flowers to put up. Lots of pics of both of these you mention, but not enough time! Poke! Knapweed! And more!
This is a gorgeous plant with one small problem – incredibly invasive, spreads aggressively, after 3 years I have regretfully pulled 90% of it out. If you plant it, be prepared for a huge network of fine white roots snaking under 1 foot wide rock borders, surrounding other plants, etc
Good to know! It sounds like Obedient Plant, which is anything BUT!
I found a blue mistflower growing near my gutter downspout here in Centreville VA behind my tomato plants ( which I’d planted in pots). I was surprised how long living the blossoms are: over two weeks. Since first noting it I have noticed quite a lot of them in the flooded area near Cub Run where I live.
Yes, now is the time for them. They still surprise me when I see them in the wild–they should be in the garden! 🙂
We’ve had a lot of rain recently in Williamsburg, VA and the Blue Mist flower “just showed up”! In the 20 years I’ve lived in this house, I’ve never had this beautiful flower come up before in my flower bed. My question is, “how did they get in my flower bed”?
I saw quite a lot of these growing wild in Pimmit Run Stream Valley, in Fairfax County, VA, and your website and great photos are very helpful in identifying them. Thanks!
My son and I saw these Blue Ageratums at the Neabsco Regional Park, along with wild grapes along the walkway to the wetlands area.