Could it be that they reseeded?

They do both...reseed and sucker. I have to keep at mine as well or they will take over.

tj

Yes indeed, they re-seed and sucker which might be a plus in some places or a negative. In my garden it led to their removal.

Yes, they definitely sucker, even into the middle of a well-trodden, compacted path. Not always easy to simply pull up.

I wish mine would sucker! I have had them for years and no suckering. I love these plants. They are so beautiful for such a long season. I plant them among other plants and they look good with everything. I even like it when they flop in among other plants on occasion. I would say these are one of the best garden plants a person can have. To each their own though.

I've also found they sucker. A word of warning though- it might be a good idea to wait until fall to remove/transplant suckers. I seem to remember trying to cut a couple suckers out from by my plant years ago and the result was that part of the main plant looked wilty afterward. Not sure if was because I cut a main "artery" (lol) or I did it in or too close to summer.
CMK

Mine did a few years back ~ dug him up/potted for a while & offered to a friend!!!

I got a dwarf (was told no such thing) that ended up a regular size ~ planted in a wrong setting had to dig up potted again offered to another garden friend! We love the scent & the making wreaths for Fall!!!

I think it's one of the plants I consider a must have.

These two were at least five years old before they started suckering. It was also after I started shearing them off halfway to encourage fuller more upright growth and flowers....

I have a dwarf 'Little Spire' and it IS smaller and has not suckered....yet....

No seedlings just suckers.