I guess you mean Eupatorium coelestinum. Very pretty but highly agressive, by both seed and roots.

Yes, very pretty and it blooms the first year from seed. I've tried it a few times from plants grown inside under lights. Unfortunately, they never survived our winters. Still - worth growing if only as an annual.

Kevin

Comes up late in the spring, and likes to travel. So it works reasonably well in the less planned parts of the garden where it can be in one place one year, and several feet over the next.

It is this one:

(It says formerly known as Eupatorium coelestinum, so yea that's the one Laceyvail)

Here is a link that might be useful: Conoclinium coelestinum

Mine is grown from seed around three to four years ago. I've noticed a pattern- a lot of the folks that are in warmer zones have troubles with invasiveness, while those in a colder zone don't as much. Mine has slowly spread outwards, but so far nothing to be worried about. I've pulled the odd seedling here and there around the mother plant.

I've come to really appreciate this plant. It looks fresh and vibrant when most else is fading. Great color contrast with the coloring foliage.
CMK

That is a great picture, christinmk. I have had a section of this for years. Love the cloud of soft blue in September, a great pairing with chrysanthemums. But, it does spread by roots and reseeds very aggressively too -- have to deadhead it well, before seeds set. Still, I haven't found control of it to be too difficult -- it won't send its roots off to pop up multiple feet away, just in the immediate vicinity, and it is pretty easy to pull or spade up to minimize the new plants.

Nice pic, CMK!

Can this plant take part shade? I have a spot in full sun for it, but now that I think about it, might clash with the colors I have there, but have an open spot in part shade where the color will work. What do you guys think?

Thanks much!

I have some fairly gravely soil around my plant, so perhaps that helps keep it in check some.

-mxk3, mine gets shade in later afternoon and it does fine. I say give it a whirl ;-)
CMK

A little too exuberant for a garden in this area, but stunning along the roadsides! Pic from last week.

Closer.

I love this flower. I planted some early last fall that have spread about a foot in each direction so far. But it is not dense, overwhelming growth and does not seem to pose a problem for neighboring plants (yet). The plants are very, very shallow rooted and are easily uprooted even when not really trying to do so (i.e., pulling adjacent weeds).

They were very late to emerge and at first I thought they were dead until I saw some growths emerging from the soil in early June.

The color sparkles and shines in the subdued autumn light.

I like this flower for the late bloom. It appeared to have spread quite a bit so expected to dig some up today when I cut it back. It hadn't really spread, the plants bushed out and looked bigger than they were and no digging out was required.

Our local university arboretum was selling this species at it's fall plant sale last month. The plants looked really healthy and I was tempted to buy one. However, I hesitated, fearing it to be too aggressive. Having read all the comments here, I am now considering trying it since I live in a cooler zone. which should keep it in check somewhat.

I have several areas in the garden where this plant grows. It breaks ground too late in the Spring for me to offer it on my annual plant sale. In an open winter with no snow cover, I am thrilled when just a bit comes through. I have no problem with it's spread because it is shallow rooted and easy to contain like monardas. Love it for it's late bloom. It looks like the annual ageratum except grows much taller. I have it in part shade and full sun and it does well. Mary