Roses are party animals. When surrounded by agreeable companions, they take on a special glow they don't exhibit when grown alone.
Good rose companions need to be more than visually compatible, however. They need to tolerate the roses' regular irrigation and feeding, but they shouldn't compete for them. That rules out plants programmed for summer dormancy like California ceanothus, as well as water-siphoners like willows. Plants with aggressive root systems like mint or red valerian (Centranthus ruber) should also be avoided. And eliminate plants that attract diseases you're trying to keep off your roses.
Two good rose companions are campanula and Santa Barbara daisy. Other perfect perennials to pair with roses: asters, bearded irises, catmint (Nepeta faassenii), delphiniums, feverfew (Chrysanthemum parthenium), foxglove (Digitalis), garden penstemon (P. gloxinioides), nicotiana, phlox, scabiosa, Shasta daisy, true geraniums, verbena, and yarrow (Achillea).
Other pretty partnerships
• A trio of white roses ― 'Iceberg', 'Class Act', and 'Sally Holmes' ― with gray-leafed snow-in-summer and white-flowered veronica and nicotiana.
• A simple hedge of pink 'Bonica' roses edged with baby-blue 'Peter Pan' agapanthus.
• Apricot-cinnamon-gold 'Singin' n the Rain' with a skirt of yarrow in mixed pastels and a few sunny yellow 'Little Maid' kniphofia spikes popping through.
• 'Lavender Pinocchio' and 'Blueberry Hill' backed with bronze fennel or purple smokebush (Cotinus coggygria) and fronted with a wide ruffle of Geranium hima-layense 'Baby Blue'.