Mountain hydrangea

Sun

Partial shade, ideally morning sun and afternoon shade. More sun is possible in cool climates if the soil stays moist.

Water

Keep the root zone evenly moist but not waterlogged. Water deeply during dry spells, especially in the first two growing seasons and when growing in containers.

Soil

Humus-rich, well-drained soil that retains moisture. Acid to neutral soil is best; strongly alkaline soil can cause yellowing leaves. Available aluminium and soil pH influence flower colour in many forms.

Height

3-5 ft (0.9-1.5 m)

Spread

3-5 ft (0.9-1.5 m)

Flowers

Early to late summer, depending on cultivar and climate. Usually flat lacecaps with small fertile flowers surrounded by larger sterile florets, in blue, mauve or pink; some cultivars are white.

Foliage

Opposite, pointed, finely toothed green leaves, generally smaller and narrower than those of bigleaf hydrangea. Some forms develop red or burgundy autumn colour.

Growth

Moderate

Care needed

Medium

• Water at soil level whenever the root zone begins to dry; do not let newly planted shrubs dry out.
• Apply a 2-3 in (5-8 cm) mulch of leaf mould or compost in spring, keeping it clear of the stems.
• Feed lightly in spring with a balanced slow-release fertiliser if growth is weak; avoid heavy nitrogen feeding.
• Choose a position sheltered from drying winds and late frosts.
• In cold locations, protect the developing buds with horticultural fleece when late frost is forecast.

Pruning. Most forms flower mainly on the previous year's stems, so avoid hard pruning in winter or spring. In spring, remove dead flowerheads to the first healthy pair of buds and cut out dead wood; if thinning is needed, remove a few of the oldest stems at the base just after flowering.

Spring

Remove old flowerheads above healthy buds and prune out clearly dead stems.

Spring

Refresh the mulch and give a light feed if needed.

Late spring

Protect tender new growth and flower buds during forecast late frosts.

Summer

Check soil moisture regularly and water deeply during dry weather.

Early summer

Take softwood cuttings from healthy, non-flowering shoots.

After flowering

Thin congested shrubs lightly, leaving most young stems intact for next year's flowers.

Autumn

Plant while soil is moist and workable; in colder regions, wait until spring.

• Plant along a woodland edge with ferns and hostas for layered foliage and summer flowers.
• Use beneath high-canopied deciduous trees where roots have enough moisture and space.
• Group several in a partly shaded border for a soft, continuous band of flowers.
• Grow a compact cultivar in a large container on a sheltered, partly shaded patio.

Garden styles it suits: Woodland, Japanese, Cottage garden, Romantic rose garden, Modern courtyard and Blues and silvers.

Plant it with: Hostas, Japanese painted ferns, Astilbes, Japanese forest grass, Epimediums and Camellias.

Wildlife: The small fertile flowers in lacecap heads provide pollen and nectar for visiting insects. Forms dominated by large sterile florets offer less food.

• Few or no flowers: late frost, winter bud damage or hard pruning can remove flower buds. Shelter the plant, protect buds during late frosts and prune lightly.
• Wilting or scorched leaf edges: dry soil, hot afternoon sun and wind are common causes. Water deeply, mulch and provide afternoon shade.
• Powdery mildew or leaf spots: improve air circulation without exposing the shrub to drying wind, water at soil level and remove badly affected fallen leaves.
• Yellow leaves with green veins: alkaline soil can restrict iron uptake. Check soil pH; use an iron treatment suitable for acid-loving plants, or grow in a container with ericaceous compost.

Toxic if eaten by cats, dogs, horses or people. Leaves, buds and flowers contain cyanogenic glycosides; ingestion usually causes digestive upset, but larger amounts can cause more serious poisoning. Do not allow pets or children to eat any part, and seek veterinary or medical advice after ingestion.

• Bigleaf hydrangea (Hydrangea macrophylla)

  Usually has larger, broader, thicker leaves and a coarser habit. Both species can have lacecap flowers, and hybrids can be difficult to distinguish.

• Smooth hydrangea (Hydrangea arborescens)

  Usually has broader, thinner leaves and white or greenish flowers, with pink in some cultivars. Its flowers form on the current season's growth rather than mainly on older stems.

• Panicle hydrangea (Hydrangea paniculata)

  Has cone-shaped flower clusters, usually opening white or greenish and often ageing pink, rather than the flat lacecaps typical of mountain hydrangea.

Hydrangea comes from Greek words meaning water vessel, referring to the seed capsules, while serrata means saw-toothed and describes the leaf margins.

Propagation. Take softwood cuttings in early summer or semi-ripe cuttings later in summer, keeping them humid and out of direct sun while they root. Low branches can also be layered. Cuttings preserve cultivar characteristics; seedlings may differ from the parent.

Accepted botanical name

Hydrangea serrata

Native range

Japan and Korea.

Sources: GBIF (CC BY 4.0) and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.