Posted: 25/06/2012 at 12:15
I'm a big fan of these plants even though they are extremely invasive, but don't worry, I'll explain how and it won't sound quite so bad.
Like all plants that can be propagated by roots, that's its main method of invasion. it doesn't run underground like Bindweed but rather, once you have it, you can't get rid of it. Any piece of root left will grow into a new plant much like Oriental poppies, so trying to move or remove the plant will result in a war you will lose. (I'm still trying to get rid of a piece of root I planted ten years back in a border, then changed my mind and every now and then, a small clump of leaves emerge in defiance.)
This plant also likes to set seed, so removing the flower spikes once they go over is a good idea even though they do offer great architecture. I usually do this in autumn when I've had my fill of the spikes. Otherwise just weed around the plant a lot. The seeds are pea size, don't travel too far and as long as you pull them up early they are easy to remove.
As for flowering, I have two established clumps in my garden that flower every year in sandy neutral soil that is probably not especially fertile and I don't often feed them because they never show signs of needing a feed. Morning and afternoon sun are best, they need sun to flower but don't like the hottest part of the day and will wilt no matter how much you water them, but will perk right back up as soon as the sun passes.