My problem with them is that in our climatic zone at least, we have a few different types and I have trouble remembering which ones are supposed to be cut back in the Fall and which in the Spring.

So some sources say, the ones with the long, cone shaped blooms (Like Phantom) are considered to be the "paniculata" variety and you cut them back after flowering. Not sure so-far how much one is supposed to cut back.

Then there are teh other ones, the ones with the big, round flowerheads, which some say need to be cut right back in the fall. Other sources say in the Spring.

You can see why the confusion.

This year, we had a very late frost which prevented the round flower types from flowering. This suggests that the flowers form on new growth and cutting back in the fall makes sense.

They sure are showy and fill in nicely.