This is a combination from RHS Harlow Carr and it is stunning. The soft flow of the Stipa tenuissima, purple heads of Allium, blue Nigella also known as love-in-the-mist, and chocolate Cosmos.
This combination needs a little attention. Although the Allium and Stipa are easy to grow in any sunny spot, Nigella an annual so will need to be re sown each year. One drawback is thatCosmos is not fully hardy and has to be overwintered in a green house and re planted in the spring.