Well the wild scabious grows on limestone if that's any help.

Thank you,is that acid?

No, limestone is alkaline. However, Cephalaria will grow at any pH, it's not particular.

I have it and my soil is alkaline as I am on chalk. but as long as it isn't too acidic it will be fine.

But don't try to get rid of it, the roots are twisted round a tree on the other side of the world.

Have you tried, Owdboggy?

Yes, dug down over 4 feet and still they went down. Noticed today that it has reappeared, despite SBK weed killer on the roots too!

I must have been lucky then as I moved a clump 2 yrs ago and nothing reappeared where I'd moved it from.