Because my anxiety prevents me from believing I have worthwhile information to share :)

Two years ago I planted one 4in pot and watered it a handful of times before midsummer. By the end of the season it was a nice 3ft shrub with yellow flowers. I left it alone and the next year there were hundreds (thousands?) of little green shoots all over my yard. The previous year I had put down cardboard and mulch to kill the grass so there wasn't much else there. I eventually gave up fighting because I'm a lazy gardener and many of those shoots became 6ft tall plants with yellow flowers. My irises didn't bloom because they blocked out the sun. Lesson learned.

I imagine it's everywhere and there's space for nothing else.