Training shrubs to grow on walls is a practice known as espalier. A gardener prunes and trains the shrubs to grow relatively flat with the wall providing support. Espalier dates back to ancient Roman times. Growing shrubs this way can help block early morning and late afternoon sunlight on walls with an eastern and western exposure. This helps insulate walls from heat build-up. The Washington State University Extension website recommends several shrubs for espalier treatment.
The flowering quince (chaenomeles speciosa) is also known as the Japanese quince and is one of the shrubs favoured for being espaliered. The shrub is believed to be native to Japan. The flowering quince is a deciduous shrub with a dense tangle of thorny branches with scarlet, rose or crimson blooms. The flowers can also be white or pink with tinges of colour.
The forsythia, also known as the weeping forsythia, is one of the earliest-blooming spring shrubs. Native to China, the deciduous forsythia has bright yellow flowers that grow all along the otherwise bare, leafless branches. According to the Floridata website, the forsythia shrub will grow well when trained to grow against a wall.
The star magnolia (magnolia stellata) is a very slow-growing deciduous shrub. In late winter or early spring the star magnolia's white flowers bloom before the leaves appear. Native to Japan, the star magnolia was introduced to the United States in the 1860s and continues to be a popular landscaping shrub from coast to coast.
The kousa dogwood is also known as the Chinese dogwood and is similar to the flowering dogwood. The blossoms are greenish with cream-coloured bracts that surround a greenish cluster of tiny flowers. The kousa dogwood is native to Korea, China and Japan and has been growing in Western gardens from 1875. According to the Floridata website, the kousa dogwood is one of the American Horticultural Society's 75 great plants for the American garden.
Several other shrubs are favoured for being trained to grow against the wall, according to the Washington State University Extension website. The shrubs include Pfitzer juniper, holly, pyracantha, winged euonymus and viburnum.