Spiraea thunbergii aka Thunberg's Meadowsweet

Spiraea thunbergii, or Thunberg spirea, is a deciduous rose-family shrub. Kew lists its native range as Korea and central and southern Japan. Several garden sources also include China in its range. In Asia, it grows on rocky hillsides. Garden plants reach 3–5 feet [0.9–1.5 metres] tall and wide. The shrub grows at a medium rate. Many branches rise from its base, forming a dense clump. Its thin branches curve outward, giving it a loose, vase-like shape.

The pale brown stems bend in a zigzag pattern. They may bear fine hairs or have a smooth surface. Narrow, pale green leaves grow one after another along them. Each leaf has small teeth along its edge. The leaves resemble willow leaves and have very short stalks. Their fine shape gives the shrub a light, airy look. In fall, leaves turn yellow, orange, or bronze. They can stay on the branches late in the season.

Small white flowers open before the leaves appear in spring. The main bloom season runs from March to April. Flowers have five petals and gather in small clusters. Groups of three to five flowers line the branches. This early display is a main reason to grow it. Butterflies visit the flowers. Brown fruits called follicles follow the blooms. They remain through winter but add little to the display.

Grow this shrub in sun or a spot with light shade. Full sun helps it produce the best flower display. It prefers moist soil that drains well. It accepts clay, loam, sand, and chalk, across a broad pH range. Poor soil and some drought do not rule it out. Wet ground, however, does not suit it. Sources place it in USDA zones 4–8 and RHS class H6. It works in mixed borders, hedges, and screens. Gardeners also use it near foundations and along sunny woodland edges. Flowers form on growth made the summer before. Prune after bloom to keep its shape and support new growth.

Care needs are low, though suckers and twiggy growth can need attention. Serious pest and disease issues are not usual. Aphids, scale, and leaf rollers may occur. Possible diseases include fire blight, leaf spot, and powdery mildew. Root rot and honey fungus are further risks. Reports differ on how well it resists deer. Plants For A Future lists no known food or medicinal uses. It also reports no known hazards, rather than proof of safety.