Not the easiest plant to find a right place where it will be happy, IMO.
Too much sun-it will fry, too much shade- it wouldn't bloom.
In my experience, the best growing condition would be: at least 4 hrs of sun (either morning or afternoon), plenty of water and somewhat loose rich soil.
As your own experience with Brunette says, plenty of sun+ plenty of water is the key to success.
In any event, it may take 2 to 4 years before plants become fully established to produce meaningfull show.
Good luck.

Well, now I know why mine never does very well - too much shade and not enough water. I've got a couple of the type with dark foliage. They limp along from one year to the next and don't spread or bloom the way I'd like them to. Might be time to dig a wallow in a sunny area for these and for a few others that like similar conditions. It's always a challenge to grow plants that like wet conditions, as our soil is pretty sandy - although there are surprising layers of clay here and there.

Thanks ego45...the one that I am having trouble with has been in the ground for 3 years, although it seems that my dogs have been trampling it. I've resisted moving it because it takes so long to establish, but moving it would probably be easier than trying to change my dogs' travel routes :-)

I have several patches - all in fairly deep shade. They seem to bloom fine, but I'm sure they would bloom better if they had more sun. I can second the advise that moisture is critical. They don't need to be wet, but if they are too dry for too long, they might die or go dormant early (mine always come back, but they are well established). I rake a big thick layer of leaves over them every fall and add more leaf mold in the spring.

Ellen, I reroute my dog's paths using those nearly invisible mini-fences made from hinged green wire in arch shaped sections. For a couple of bucks, I can put a little barricade around a choice plant or a newly planted sapling or division. He could step over these, he's pretty tall, but he generally goes around instead - I think the green wire confuses him just a little - it makes him think he won''t know where it is in relation to his feet.

I get these at the hardware store and usually use 3 panels to make a triangle around whatever I need to protect. They're good for plants that flop, too, and really easy to get into position (even after the flopping has happened). And, they really can't be seen except around narrow, upright plants.