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Hydrangea serrata is a deciduous flowering shrub of medium size native to east Asia. It is widely used as a landscape and garden plant in many countries. Common names for Hydrangea serrata include mountain hydrangea, blood-on-the-snow, and tea of heaven. This hydrangea is a close relative of the better known large leaf hydrangea, Hydrangea macrophylla. Flowers, stems, and leaves are smaller on Hydrangea serrata, but it is a hardier species and can be planted in areas too cold for Hydrangea macrophylla.
A spot with well-drained, fertile soil is ideal for this shrub. It does best in partial shade, but will tolerate full sun if the soil is not allowed to dry out. Hydrangea serrata reaches a height of 3 to 5 feet (about 1 to 1.5 m) and usually is as wide as it is tall, growing into a round mound. It can grow up to 18 inches (about 45 cm) a year in favorable conditions. The dark green leaves are oval-shaped, up to 6 inches (about 15 cm) long, and have a toothed, or serrated, edge which gives the species its name.
Hydrangea serrata flowers are actually clusters of florets and are shaped like snowballs or lacy caplets. Sterile and fertile florets are mixed in the clusters, and the sterile ones are slightly showier. Flower color depends on the acidity of the soil where the plant is growing. In very acid soil the blossoms are blue, while in more alkaline places they bloom in shades of pink. Some flowers may be white, or white shading into blue or pink.
Within its native range of east Asia and Japan, Hydrangea serrata grows in cooler areas up to 5,000 feet (1,524 m) above sea level. In North America it is usually recommended for USDA plant hardiness zones 6 and 7, but can be planted as far north as zone 5 if it is provided with adequate winter protection. Following particularly cold winters flowers may be sparser than usual. It has been successfully grown as far south as parts of zone 9 when planted in a shaded area and given plenty of water.
Hydrangea serrata blooms mostly on old wood, the stems that grew in earlier years. To encourage best blooming the only routine pruning should be removal of dead or damaged stems. It is a summer flowering shrub, and the blossoms are most profuse in July and August. The flowers are pollinated by insects.