There are also about a dozen different daylilies planted between the other perennials, a number of Hostas ... for the lovely leaf variations and sizes... and a few low, edging plants (including a low-growing sedum Rock 'n Low 'Boogie Woogie' and sedum 'Little Miss Sunshine'... Artemisia schmidtiana 'Silvermound' and Ajuga reptans 'Black Scallop' for contrasting foliage and texture... Allium 'Summer Beauty' for a different shape in flower form (round)... Astilber chinensis 'Visions in Red' and lupines for their leaf shapes and texture, plus plume / spike flower forms... and even Dwarf Shasta Daisy 'Macaroon' for its disc-shaped contrasting flowers.
I have planted multiples of each... although, with the Delphiniums (for example), there are three of them - yet, all different: Juiliette, Shelby and Glitzy. With the lupines, scattered along the edge, differents shades of colours. Even the Hostas and foliage, and the edging plants are planted in repetition... but not symmetrically (not opposite to each other on the opposite sides of the walkway). I do not plant for 'matchy-matchy' symmetry (mirror image to each other) ... but rather, for balance across the whole of the view. Repetition to tie the edges and opposite borders together, but with the same plants staggered along the whole of the borders. Or repeat a bloom colour (Vision in Red vs. My Fuzzy Valentine daylily) or with foliage... such as Artemisia schmidtiana 'Silvermound'... which echoes Stachys byzantine 'Helen von Stein' with silver leaves.
And I plant for blooms along an extended season... from early bloomers to the sedums and Baby Joe-Pye Weed into the fall. I try to layer the textures and flowers, too, from ground to sky... with climbers on the fence and arbors, taking the border vertical as well.