Such a coincidence! I've just come in from the garden and just a couple of months ago I put in 1 evening primrose plant and I've just noticed I've now got 3! That's in such a short time that I was amazed when I saw them. They're not invasive though in the line of taking over the garden. They're individual plants that can easily be moved or pulled up, not like a particular form of campanula I made the mistake of planting. They call it ground cover but they don't mention that the roots will spread like wildfire and they are almost impossible to get rid of!