Sweet William is a nice plant for a cottage garden, but also does well in pots. The flattened small flower heads bloom compactly together and form dense screens. If you prune the sweetheart completely back after flowering, it will flower again.
Dianthus combines nicely with, among others such as, Saponaria, Cheiranthus), Poppies, Coreopsis, Gaillardia and Malva.