Remember, too, that foliage has color and may be green, blue, red or gray. Perennials can range in height from several inches to many feet. Space them so that they are just touching when mature. The small or ferny leaves of such perennials as yarrow and astilbe have fine texture, which creates a feeling of airiness. The large leaves of hollyhock by contrast are coarser and create a feeling of solid space.
Flowers also vary in texture, as does foliage.
Perennials may be classed as spiked, rounded or ground-hugging. Combine a variety of these for interest. Mix upright balloon flowers or lupines with mounded gaillardia or doronicum, bordered by low-growing sedums or candytuft. Some exceptions, like coreopsis and gloriosa daisy, will bloom over a very long season. Many gardeners plant for a succession of bloom, such as primrose for April, foxglove for May, poppy for June, scabiosa and daylilies for July, phlox for August, liriope for September and chrysanthemums for October.