Tall Black and Green Plants
That is indeed the very one
... a lovely thing
Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.
I really like the Scabious Chile Black (60cm) which would look good tucked away in the grasses. Is there anything similar but taller that flower in the summer months ?
The closest I can find is Sanguisorba which rises to 120cm but that is more deep red than black.
Totally into Eupatorium 'Chocolate'--I think it now goes under the name of Ageratina 'Chocolate'?
One of Piet Oudolf's best genera is Sanguisorba. For a tall one, how about this:
While not black-flowered, you could also use black-foliaged things, such as Anthriscus sylvestris 'Ravenswing' or Angelica 'Ebony' to make a wonderful effect.
Verbena bonariensis and Salvia uliginosa are excellent as tall plants between grasses, as is Vernonia:
. These don't have black or green flowers but will disperse well among grasses.
And there are lots and lots of asters/former asters to play with available from Knoll Gardens and Beth Chatto via the links above.
I also have a personal weakness for this Eryngium. It's a bit of a hulk, but amazingly spectacular: