Oh, I'm sorry to say that I have had BOTH of these plants and I have almost eradicated all of them. I used round-up (when possible) and I snipped off every green leaf as soon as I saw them sprouting up so that the plants eventually died off. I had an easier time killing the soapwart than I did the ageratum. Now I am on a mission to eliminate all of the alstroemeria that keeps popping up amongst other plants. Now THAT one is really difficult because the little peanut-shape tubers are brittle and break off.
Persistance will pay off. I have eliminated running bamboo and obedient plant using round-up and a vigil eye.
good luck,
molly

I do love the hardy ageratum but they do need their own LARGE area in a Large garden. Definitely not for any shared spaces. Been there, done that. Keep digging.

Thanks guys for this post! I just went out and moved the Blue mist flower I planted last year to a less hospitable area. It was looking just TOO happy. Now I think we'll both be happy, me especially :-)

Plants like the ones mentioned do take persistance to remove, but it eventually pays off.

I'm not a lover of chemicals, but on some plants that are difficult or impossible for me to dig out, like poisen ivy and deep rooted hackberry seedlings, I apply a drop of full strength broad leaf weed killer to either the cut off stem or new growth. That usually takes care of it, although sometimes a second or third drop is needed.

Another is obedient plant. It was one sick son of a gun who named that one.
It is almost gone and I an still fighting the blue mist.

Haha, I just realized you had mentione obedient plant.
I just read that it is called obedient because it bounces back if you bend it over.

Kathy

Thanks for the responses, I'm so glad I'm in good company. I have a talent for choosing invasives, I also have obedient plant, pink mexican petunia (That one was a stowaway, but I let it live), lemon balm, and of course mint.

I think I'll be resorting to careful Round Up usage otherwise I'll be digging for several lifetimes. Sigh.

Round up can be applied in a crowded flower bed by using a small paintbrush. It will not migrate to neighboring plants.

gee. I love both of those plants!

I'm growing both. The bouncing bet I knew was crazy so I put it where it could do that whole aggressive ground cover thing where I didn't care. I didn't know the blue mist was so it's might end up corraled in a pot (with a saucer under it) in the "tamer than most" bed. I haven't decided yet. All of the plants here have some aggressive tendencies so I might just be able to "weed out" where I don't want it before it clobbers the other plants. The blue mist (gregg's blue mist btw) with it's apple green foliage and fluffy purple flowers that attract so many butterflies is just too pretty to give up.

Blue mist doesn't like being trampled. I had some growing around the pond filter and after dh worked on the filter one weekend, there is almost none left.

Opps... I was confusing soapwort with spiderwort.
Don't grow the soapwart. But I do love the bluemist. Just pulled a bunch out of one bed to spread around in the others. Its so easy to pull up where ever you don't want it.

Bluemist is one of the few plants hubby comments favorable about due to the butterflies all day long all summer and fall.

I love bouncing betty. I have it planted in the front bed, full sun, no water, and it loves it. Its too hot there for anything else to survive. Barbra

I love the blue mist flower too. but combined with the bouncing bet in the same bed--not a good idea! My bouncing bet has thick ropelike yet brittle roots, making it very difficult to just pull out, and it's all tangled with the blue mist flower.
My blue mist is covered in butterflies during bloom time. And I agree, the bright green foliage is an added bonus, it's such a pretty plant.

I use a small paintbrush with the round-up and just dab a tiny dot of it on the cut growing tips of the blue mist flower. It'll kill a big patch of the stuff, every part of the plant that it's connected to by roots. Just be careful to attack a tip that doesn't touch any other plant or the round up will kill that one too, especially if it's one that you want to keep. Cheryl