mine are in a rrockery in full sun and come up every year

Yes, they need full sun. Be careful with these, though. They can become invasive!

Bloom well in full sun, multiply out of control. Beware!

i have some in semi shade and they do ok too.

Come to think of it, I have M. latifolium in semi shade and they're doing OK so far...and they are not thuggish!