On rare occasion invasive might be okay. There is competition from large shrubs at the top of the hill and only morning sun, so not much will grow there. I only planted 2 vinca and will watch them closely. A friend of mine has had trouble with it, so I know it has the potential to be a pest. I thought long and hard before planting it. Good to know about the phlox. I lay a dripline in the spring and summer to provide moisture, but it probably still is dryer under all the shrubs. We shall see.
