Spiraea japonica is one of several Spiraea shrubs with alternate, simple leaves, on wiry, freely branching, erect stems. Stems are brown to reddish-brown, round in cross-section and sometimes hairy. The shrub reaches 1.2 m to almost 2 m in height and about the same in width. The deciduous leaves are generally an ovate shape about 2.5 cm to 7.5 cm long, have toothed margins, and alternate along the stem. Clusters of rosy-pink flowers are found at the tips of the branches. The seeds measure about 2.5 mm in length and are found in small lustrous capsules.
It is naturally variable in form and there are many varieties of it in the horticulture trade. So far, nine varieties have been described within the species.
Spiraea japonica is a deciduous, perennial shrub native to Japan, China, and Korea. Southwest China is the center for biodiversity of the species. It is naturalized throughout much of the Northeast, Southeast, and Midwest areas of the United States, and parts of Canada.
A common habitat for S. japonica in general seems to be in riparian areas, bogs, or other wetland habitats. It is found growing along streams, rivers, forest edges, roadsides, successional fields, and power line right-of-ways. It prefers full sun, but can tolerate partial shade. It prefers lots of water during the growing season; however, it cannot tolerate saturated soils for extended periods of time. It prefers a rich, moist loam, but it can grow in a wide variety of soils, including those on the alkaline side.
It is a common ornamental, with numerous cultivars being selected for garden use. The tall forms are grown as hedges, low screens, or foundation shrubs. The low-growing forms are used as groundcovers or in borders. The following cultivars have gained the Royal Horticultural Society's Award of Garden Merit:-
Spiraea japonica has become naturalized in North America and occupies habitats similar to those of native spireas. It aggressively invades disturbed areas and forms dense stands that outcompete native species. It often spreads locally when its hardy seeds are transported along watercourses or in fill dirt.
Once established, S. japonica grows quickly and forms dense stands that outcompete much of the existing native herbs and shrubs. The seeds can last for many years in the soil, making its control and the restoration of native vegetation especially difficult. Growing populations will creep into meadows, forest openings, and other sites.
- "Spiraea japonica". floridata.com. Retrieved 2008-10-08.
- "Spiraea japonica (shrub)". Invasive Species Specialist Group. Retrieved 2008-10-08.
- "Japanese spiraea". National Park Service. Retrieved 2008-10-08.