Hydrangea serrata var. serrata (mountain hydrangea, "Yamaajisai")

Japanese name: ヤマアジサイ （山紫陽花）
Scientific name: Hydrangea serrata var. serrata

[Overview]
A deciduous shrub 1–2 m tall.
It branches freely from the base, and the branches are slender.
The leaves are simple and opposite, oblong to ovate-elliptic, 10–15 cm long and 5–10 cm wide, with triangular teeth on the margin.
The upper surface of the leaf is slightly glossy, and there are 4–7 pairs of lateral veins.
The leaf stalk is 1–3 cm long.
Cymose inflorescences 4–10 cm across are produced at the branch tips.
The inflorescence has 4-petaled sterile flowers 1.5–3 cm across around the edge and many bisexual flowers in the center.
The sterile flowers are white or pale blue, and many later turn pale pink.
The bisexual flowers are 5-petaled, white to pale blue, with petals that fall easily, and 10 stamens of the same color as the petals.
The fruit is an elliptic to ovate capsule 3–4 mm long.

[Cultivation]
Propagate by division or cuttings.
It prefers partial shade and moist, fertile soil that is well drained and retains water well.
It tolerates shade, but flowers less freely.
It is unsuited to places where the soil becomes extremely dry or that receive strong afternoon sun.
It absorbs a lot of water, so for potted plants take care that they do not dry out, and water thoroughly when the soil surface dries.
Plants in the ground do not particularly need watering, but during the hot season in summer water them in the morning or evening when the temperature is low.
Apply organic fertilizer twice a year, in winter and before flowering.
Pests and diseases include powdery mildew, anthracnose, mosaic disease, leaf spot, scale insects and aphids.

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