739 Spiraea japonicaCommon Names: Japanese spirea, Japanese meadowsweet, maybush Family: Rosaceae (rose Family)
Japanese spirea is an erect, multi-stemmed deciduous shrub that gets 2-6 ft (0.6-1.8 m) tall with a similar spread. The slender reddish brown stems may be hairy or glabrous. They bear alternate ovate-lanceolate leaves that are 1-3 in (2.5-7.6 cm) long and usually paler on their undersides. The leaves have toothed margins, wedge-shaped bases, and pointed tips. Leaf color varies from chartreuse to blue-green to bronze, orange, red, or burgundy with variety and season. Flat-topped clusters (corymbs, to be technical) of pink flowers are displayed at the tips of the wiry branches. In the most common forms, the pink color results from a mix of light and dark pink that gives the blossom a pixilated appearance. Small lustrous capsules hold seeds about 1/10 in (0.25 cm) long.
The species Spiraea japonica is an upright shrub, 4-6 ft (1.2-1.8 m) tall. Noteworthy cultivars include: Bumalda spirea (cv. 'Bumalda'), which is a spreading shrub, only 2-3 ft (0.6-0.9 m) tall; 'Alpina' or Daphne spirea - a low, dense, spreading, slow-growing groundcover type with pink flowers and small bluish-green leaves that turn red and orange in fall; 'Magic Carpet' - a compact shrub that has dark pink flowers and leaves that emerge red, mature to bronze, then change to deep red in the fall; 'Neon Flash' - a rosy-red-flowered 4 ft (1.2 m) shrub with leaves that start out reddish and retain a purplish tinge; 'Shibori' or peppermint stick spirea - a low mound-shaped shrub that bears multi-colored white, pink, and red flowers all summer; 'Anthony Waterer' - a 2-3 ft (0.6-0.9 m) bush with maroon-tinged foliage and reddish-pink flowers; 'Dolchica' - a 2 ft (0.6 m) shrub with bright pink flowers and deeply incised leaves that emerge purple; 'Froebelii' - an especially cold-tolerant (to Zone 3) variety that has purplish new growth and produces rosy-pink flowers off-and-on through the early summer; and 'Goldmound' - a compact 1-3 ft (0.3-0.9 m) pink-flowered shrub with creamy chartreuse-yellow foliage that turns rusty gold with red tips in the fall.
Not surprisingly, Japanese spirea, Spiraea japonica, comes from Japan. It also is considered native to Korea and China. It has naturalized in North America from New England south through the Appalachians into Tennessee and Georgia, and west to Indiana. Japanese spirea usually grows along stream bottoms and on seepage slopes, but readily invades mesic forest edges and openings, old fields, roadsides, and utility rights-of-way.
CultureJapanese spirea will grow in a wide variety of soils, including those on the alkaline side, but it prefers a rich, moist loam. These shrubs appreciate manure and thrive on organic mulch. Since they bloom on the current season's growth, Japanese spirea should be pruned in winter or early spring. They can be cut all the way to the ground. After the flowers fade, shear them off to stimulate a second flush of growth and more flowers. Mowing will control expansion of a planting, but the stems will resprout, so repeated cutting will be a longterm necessity. Spireas may suffer minor damage from a variety of pests and diseases, but they are not prone to any major problems. Aphids occasionally are a nuisance in the spring. Light: Partial shade is okay, but full sun promotes flowering and good leaf color. Moisture: Japanese spirea likes lots of water during the growing season but will not tolerate saturated soils for extended periods. Hardiness: USDA Zones 4 - 8. Some varieties are hardy into Zone 3. This is a plant for temperate climates with distinct winters. It does not do well in the extended warm weather of the subtropics. Propagation: Japanese spirea reproduces aggressively in the wild. A single plant can produce hundreds of seeds that remain viable and persist in the soil for many years. Typically the seeds are dispersed by water and deposited along stream banks. They also are distributed in fill dirt. In cultivation, Japanese spirea usually is propagated by sucker division or softwood cuttings rooted under mist in a warm place during the summer. Hardwood cuttings can be rooted outdoors in the fall. This plant also may be layered by pegging down a branch in the spring and potting it up in the fall. Spireas are easy to transplant. Fall is the best time to divide plants, but spring and fall are both good for setting out new ones.
Tall forms are grown as hedges, low screens, or foundation shrubs. Low-growing forms are used as groundcovers or in borders.
Varieties of Japanese spirea with yellow leaves are excellent for brightening a planting and providing contrast to dark-foliaged species. There are about 100 species of spireas. The popular Reeves' spirea (S. cantoniensis) blooms in early spring with white flowers.
Japanese spirea can be an aggressive invasive plant in a damp temperate climate. The Plant Conservation Alliance lists this species as an Alien Invader. It will elbow out delicate border companions and try to creep into the tall grass at the edge of the lawn. It takes over disturbed areas quickly, then slips into nearby meadows, forest openings, stream bottoms, and the like. Once established, it grows rapidly and forms dense stands that out compete native vegetation.
Linda Conway Duever 7/22/00; updated 12/26/03, 6/8/11