http://apps.rhs.org.uk/advicesearch/profile.aspx?pid=99

This RHS page seems to say it all.

mine are in a couple of borders that are humus rich and free draining. And they fare quite well, They are also in borders that are protected from drying winds and they don't get too much frost.

And unless you want a gillion seedlings all over the place, remember to dead head when they have finished flowering and before the seed falls. I was unable to do it 2 years ago and I am still pulling out dozens of them.

Never been able to get them going in my garden. Probably due to my clay then.

At Gt Dixter they were quite near the edge of a large herbaceous border and seeding between stones on the wide pathway. I believe Christo used to do the extraction of these seedlings until he got too old for it. I should think they sold well in the plant sale area. I got mine from RHS and I think I have lost one of 4 plants. They are in a crowded herbaceous border. I seem to remember reading somewhere that they hate being crowded while small. They do get rather large, given the right setting...... space while getting ready to pile on the growth.

Can I join in and say thankyou Norman for the question and Inverglen for the link - tells me just what I've been needing to know as well.