As I posted on another forum,I am fairly new to gardening and several years ago I was shopping for plants to fill several beds. Money was a little tight so I was pleased to find that pink dragonflowers were self-seeding.I ordered three (maybe six?) and planted them in the corner of one bed. They were very pretty. I covered the bed in the fall and when I removed the mulch in the Spring I had hundreds of two to three inch high plants growing all over. I waited until they were a little bigger so I could identify them by their foliage and it turns out they were dragonflower. I gave literally dozens away (with a warning) and threw at least that many more away. I have thrown away 75-100 this year. They apparently have a complex root system that makes it nearly impossible to remove them without damage to the surrounding plants. I find it strange that the white flowered version of this plant is said to be nowhere near as invasive as the pink. However ,I don't personally intend to find out.
My no.1 worst