Sedum 'Stardust' would look good in the top terrace with the delphiniums. Late summer flowering, so you would have something flowering from May to Sep. could also think about adding a few bunny tail grasses to this terrace too.
Sedum 'Autumn Joy' sedum is a drought-resistant perennial flower that grows well in most soil types, even dense clay. Plant it in full sun for best results. Its late-summer blooms attract butterflies. Name: Sedum 'Autumn Joy' Zones: