Spiraea nipponica aka Snowmound Spiraea

Spiraea nipponica, or Nippon spirea, is a deciduous shrub. It belongs to the rose family, Rosaceae. Its native range includes Honshu and Shikoku in Japan. It grows in a temperate climate and sheds its leaves each year. Gardeners grow it for its dense shape and white flowers.

Size varies among the species accounts. Larger garden plants reach 5–8 feet (1.5–2.5 metres) tall. Their spread reaches about 8 feet (2.5 metres), sometimes slightly more. UConn gives a smaller range of 3–5 feet (0.9–1.5 metres). The shrub forms a dense mound or an upright vase shape. Its arching stems branch mainly from the base. RHS gives five to ten years to reach full size. Stout stems have reddish-brown bark with ridges and peeling strips. Buds lie close against the stems.

The small, simple leaves grow in an alternate pattern. Their shape ranges from oval to broad near the tip. Rounded tips may bear a few teeth. The upper leaf surface is dark green, with blue-green beneath. Leaves turn yellow in fall, but offer little fall interest. Small white flowers crowd the stems in rounded clusters. Each flower has five petals. The main bloom season runs from May into June. The flowers attract butterflies and stand out against the leaves. Brown capsules follow the flowers and remain through winter. These fruits add little to the garden display.

Grow this shrub in full sun or light shade. Some afternoon shade suits sites with hot summers. It prefers moist soil that drains well. It accepts clay, loam, sand, and chalk. Acid, neutral, and alkaline soils can all suit it. Sources describe it as easy to grow with low upkeep. Chicago lists USDA zones 3–8; Oregon State gives zone 4. RHS rates its UK hardiness as H6. Use it in borders, foundation beds, or groups. It also suits low hedges, screens, and woodland planting. Cuttings provide a way to raise new plants.

Serious pest and disease problems are not usual. Aphids, scale, and leaf rollers can still attack it. Possible diseases include leaf spot, fire blight, and powdery mildew. Root rot and honey fungus are other risks. Sources also report deer resistance and tolerance of clay soil. They list erosion control among its landscape benefits. The supplied evidence gives no basis for edible uses. It also does not establish safety for people or pets.