PlantFiles: Hardy Ageratum, Blue Mistflower
Conoclinium coelestinum

WAYYYY too invasive, i'm still trying to pull all the underground roots !!!

I grew this plant from seed in spring and they are blooming wonderfully right now. I used cold treatment and they germinated well. The resulting plants are in a spot that had full sun with a little shade later in the day - while the sun was high in the sky during early summer. Now that it is fall and the sun is lower they get part shade from nearby trees. I hope these are hardy here and reseed because in my opinion, you need a lot to have a nice show of blooms. If they aren't hardy for me I would grow them again as an annual. I've seen them being described as a moist site plant, but they've performed good enough for me with dryish sandy soil.
They need to be placed towards the front of a border, hopefully with a slightly lower growing and long blooming plant in front of them. Mine are in front of and kind of mixed in with Iris and they look nice together. I like the airy effect they have in the garden.
I doubt they would be invasive in a colder zone like 5 or 6. Plus where they are a native, they technically couldn't be. The only place that considers them to be a noxious weed is Kentucky. Although one man's weed.... is another man's treasure : )

Blue mistflower ("Conoclinium coelestinum), the are great fillers that require no care but you want to place it in a confined area to keep it under control. It add valuable color to the Fall garden!
http://www.arthurinthegarden.com

These beautiful wildflowers are common in wet hammocks and pond margins throughout the state of Florida.

I got a bit of this from a friend because I love the color in late summer. I put it in a dappled-shade location and it has taken off. To prevent its smothering my precious primula I'm taking out a hunk to plant on our condo grounds. We have terrible soil--silty acid junk with awful drainage--so we try spreaders in shady areas where grass just won't grow.

I got a start of the hardy ageratum several years ago. It does well for me here in north-central Indiana, but I haven't had a problem with it being invasive, possibly because we are in zone 5. I really love it, and so do the butterflies!

A friend of mine gave me this last summer and it bloomed big and beautiful. Now I am picking out millions of seedlings... and I find I can't just pluck out a little seedling but I have to dig down at least 4-6 inches as the roots go 'way down and I find a mass of white roots ready to spring up more seedlings. She has more shade and I don't think hers spreads like this. Mine are in full sun and are everywhere now!!!

This lovely plant grows wild on my property & throughout this area of Virginia (the Piedmont).

The fluffy little violet flowers are a wonderful accent in the late summer/early fall wildflower landscape, & the stem length makes it a nice addition to indoor bouquets.

This is a beautiful fall-blooming plant that attracts butterflies and hummingbirds. It does have a tendancy to spread, but you can keep it in check. It is also easy to dig some up to give to friends or put in other parts of your garden.

Lovely addition to the garden for its late summer/fall flowering. Although it can be invasive in some areas, we have ours planted in a border in non-amended soil and in 4 years it has not invaded its companions. Nice cut flower for fall arrangements.

I tend to like this plant because it is very carefree - it grows wild in a nearby cow pasture. However, it can be a thug, so watch that you don't plant it near something that has a delicate constitution. And don't feed or water it too much - thin, dry soil will help keep the growth in check.

This plant is highly invasive in loose to medium soil. The beautiful flowers in late summer and autumn help to compensate for trait, though. Grows and flowers well in full sun to medium shade, wet to dry. A wonderful addition to a meadow or natural wildflower planting area large enough to accommodate a beautiful wildlife attractor.