The best way is to use some traditional herbaceous perennials, ones that don’t spread, to flatter your roses. Choose some that flower before the roses appear and some to carry on afterwards ensuring colour from May until October. The carpet of foliage produced by your perennials will also help to deter fungal diseases like black spot because spores are less likely to be washed back up from the soil to rose if there’s a leafy layer between.
The colour blue flatters every rose (whatever the colour) and one of the best support acts is the violet-blue Campanula lactiflora ‘Prichard’s Variety’. It produces clusters of bells in early summer but will repeat flower, if cut back, until late into the year (75 cm - 30 inches). Two sterile hardy geraniums, ‘Orion’ and ‘Rozanne’, will also produce a wave of blue from May until late autumn and they could be used in front of roses. Compact lavender, like ‘Hidcote Purple’, or the billowing catmint Nepeta ‘Six Hills Giant’, also provide waves of blue and both can be cut back in early May to delay flowering until July, so that they follow the first flush of roses.
Early May performers could include forms of the winged violet (Viola cornuta) and there are white, pale-blue and pink forms of this cushion-forming viola. Peonies also blend well and their foliage outlasts their May or early June flowers. ‘Festiva Maxima’ is a fabulous performer and the pale-pink, heavily petalled blooms fade to blush-white. The magenta-red flecking found on this peony picks up the colours of old-fashioned roses. Foxgloves (Digitalis purpurea) also blend well as their bells are usually spotted in maroon and white. Dark-red astrantias are also excellent with paler roses and there are several good forms including ‘Hadspen Blood’ and the clearer red ‘Ruby Wedding’.
For late-summer and autumn splendour use penstemons as they will continue to flower. Varieties vary and some have large, almost-clumsy wide-mouthed bells. Others are neater and ‘Hidcote Pink’ and ‘Evelyn’ are both good, elegant pinks. The ruby-red ‘Garnet’ (which is now correctly called ‘Andenken an Friedrich Hahn’) is a wonderful performer. I would also recommend the smoky, lilac- blue ‘Pennington Gem’ and any good white on offer.
Dark, sultry roses can be enhanced by blush-white flowers and you could use the ethereal wands of Gaura lindheimeri or the pink-eyed white Verbascum chaixii ‘Alba’. Pale roses need a dark contrast. The wine-red buttons of Knautia arvensis, the dark-blue spires of Salvia verticillata ‘Purple Rain’ and the ruby-red heads and dark foliage of Sedum ‘Purple Emperor’ will add infusions of deep colour late into the year.