Mike, love Helenium; me too.
I think the combination of lots of sun and sprinkler systems worked well, for me, in the big gardens. In addition, I think the clumps I ended up with need division, maybe every five years, to maintain their height/vigour. Heleniums are quite shallow rooted, so it's not so hard to dig up clumps with a spade, chop them up and replant less with upgraded soil. I also feel that heleniums tend to loose out, in competition in mixed perennials, with tougher garden perennials.
