Rudbeckia fulgida ‘Goldsturm’ – With a name that translates as ‘gold storm’, you know you can expect a flurry of thin-petaled golden yellow daisies contrasted by dark brown cones. These are borne July to October and work well with Pennisetum ‘Hameln’, or for a little more contrast, try Japanese Blood Grass (Imperata ‘Red Baron’). Grows 24-30″ high and wide. Zone 4.
Geranium ‘Rozanne’ – This 2008 Perennial Plant of the Year was discovered in Somerset England in 1989. It features large blooms of violet-blue (with a white eye) from May to September, which means that it is still in flower when many of the warm-season grasses are in their prime. Pair with the golden Hakonechloa ‘Aureola’. Grows 16-20″ high by 24″ wide. Hardy to zone 4.
Helenium x ‘Double Trouble’ – This Dutch introduction of Sneezeweed (used to be used for snuff) bears sterile blooms of bright yellow with layered petals surrounding a green to golden cone. These have strong stems and make good cut flowers but may require staking in fertile soils. It is shown in combination with Purple Fountain Grass. Grows 30″ high by 18-24″ wide. Z4.
Perovskia atriplicifolia ‘Little Spire’ – This compact Russian Sage is less prone to flopping over and features airy violet-blue flowers over much of its stems from midsummer to frost. The pungent silvery foliage contrasts well with other plants and is quite drought tolerant. Pair with dwarf gold-banded Miscanthus such as ‘Little Zebra’ or ‘Gold Bar’. Grows 18-24″ high and wide. Zone 5.
Coreopsis verticillata ‘Zagreb’ – An RHS Award of Garden Merit winner covered in 1″ wide bright yellow daisies (from June to September) which also attract butterflies. Absolutely eye-catching when combined with Lavandula ‘Hidcote’ or Blue Oat Grass (Helictotrichon sempervirens). The airy green foliage doesn’t overwhelm adjacent plants. Grows 15-18″ high. Zone 4.