It sends out underground runners eventually. I've had blooms, but don't even know what seeds might look like.

When I start yanking a volunteer, I trace its rhizome as close as I can to the mother plant and remove the whole thing. Since I thin 1-2 times a year the volunteers and their roots are not too hard to pull, esp. after a rainy day. It might not be so labor intensive if perhaps one potted and sank the pot inground for control, but I wouldn't b surprised if rhizomes eventually tore thru plastic pot. It's not entirely out of the question that I'll remove all together if too weak or sick to do the yearly battle but for now I don't mind too much