I had a similar experience. It spreads vegetatively and also by seed quite vigorously in my garden so I totally got rid of it. ( . . . and I have a fair amount of area in garden, but it was just way too vigorous !)
Here's what I did:
I dug up all the big and small chunks I could with a sharp shovel (You can move a chunk or two to where you want it if you want to keep some.) Then kill whatever is left by religiously breaking off every sprout as it comes up. It's a nice morning coffee kind of activity if you don't mind a little mud in the morning. It only took me about a season and a half to get it all gone, much quicker than the valerian or goose-necked loosestrife, two other conquer-the-garden type of plants. It only took a very few minutes a week, but you can't let it go for long or it will start building strength again.

Best wishes! (Wouldn't it be nice if nurseries warned us before we got into trouble with plants like these?)

I wish my JPW would take over (ok, I know...watch what you wish for), but then again grasses and shrubs have been shading mine. I have plenty of space, I should probably move them to where they would get more sun (and have plenty of room to grow uninhibited). I'll put them on the list of plants to move...which is quite long at the moment!
Tara

Uh-oh. Valerian was invasive? I just planted some seedlings for its fragrance. It was one of the plants I was highly aniticipating. Time to do some research.

I can handle invading by seedlings. I hate invading by roots that run everywhere, like mint and tiger/ditch lilies. Which kind of invasive is it?

P.S. Your 'dwarf' JPW doesn't seem too dwarfy!

My 'Little Joe' Eupatorium also proved to be taller than advertised. I moved it last fall and it has not shown up yet. I'm starting to think maybe I don't want it to. [g]

Don't worry, Deanna. Valerian is a seeder, not a runner. I was given a pl ant by a friend, and as you may have realized by some of my comments, I'm really bad at deadheading promptly. I really liked the tall white lacy flowers, but it seeded everywhere. I pulled a pl ant up last weekend, and it's probably been close to 10 years since I wanted it in the gar den, so it's pretty persistent.

PM2 - Eupatorium seems to be one of those pl ants that only is a seeding problem in certain areas. Some folks find it never seeds for them, but I'd never voluntarily plant one in a gar den again. I do have 2 varieties that grow in a wild area (floodplain) that I love. The seeding doesn't seem to be variety dependent, only location. Where it's happy, it's REALLY happy. ;>)

Thanks for all the responses. I guess I'll get my shovel out and try digging again. :-)

Deanna-
YES on the invasive valerian. But since I, personally, love it in June, I let it go. I'm all about anything fragrant in my garden, and I like this one. Bring it to the swap...

Well, I've been on the fence about getting rid of it completely. I really don't have the room for it, but I'm so stubborn. lol I just love that plant and wish I had room for it. But now that I hear about these experiences, I have been eyeing that space for something else, so I think I will dig it out and not wait to see if it comes up later. Would enjoy seeing pho*tos of yours Babs, when it blooms this year.