Blue is one of the best color companion roses. English gardens often have blue flower as companions to roses. Blue delphinium, a tall perennial with a long, lush flower head, is one of the better choices as is the easier-to-grow annual the larkspur, which is available in several shades of blue. Blue Hill and Blue Queen salvias are other good blue companions.
Silver and Lavender
Plants with silver foliage combine well with roses. Cat mint (Nepeta faassenii) is a classic companion. With blue flowers blooming in June and August, it has a rounded, branching habit and silver-touched foliage. Lavender-colored plants are also common companions, especially deep-pink roses. Pink dianthus alwoodii, a perennial, all-season bloomer with clove-scented single or double flowers, is one example. Munstead Lavender with blue-lavender spikes is another.
When room exists around roses, shrubs are good rose companions. If the shrubs are flowering, such as lantana, select colors that work well with roses, like lavender and blue-lavender. Select nonflowering shrubs for foliage colors. Examples are the blue-green foliage of Wilton's juniper or yellow-green foliage, of old gold juniper.
Other Color Companions
Low-growing annuals with season-long color constitute other companions. Petunias and violas in colors favored by roses add charm as they peek out from the base of a rose bush. Victoria blue salvia makes an excellent color companion. Vines, like clematis, work especially well on trellises or arbors behind roses.