8 named cultivars

shrub

Mountain Hydrangea

The Story

Plant Bio

Hydrangea serrata, the mountain hydrangea, is a compact deciduous shrub from the mountain woodlands of Japan and Korea. It forms a rounded clump 2 to 4 ft high and wide, with slender stems and pointed, finely toothed dark green leaves. Flat lacecap heads of small fertile flowers ringed by showy sterile florets open through summer.

It is smaller, finer-stemmed and hardier in bud than the mophead hydrangea, so it flowers more reliably after a cold spring. Sepal colour follows soil chemistry, blue on acid ground and pink on alkaline. NCSU lists the plant as poisonous, and the buds and leaves contain cyanogenic compounds.

Uses & Benefits:

Delicate lacecap heads over neat foliage on a shrub small enough for a courtyard, with sepals shifting blue or pink with soil pH.

Hardier in bud and more compact than mophead hydrangea, so it flowers more dependably in cold springs and small spaces.

The fertile inner florets of the lacecap heads are genuinely useful to bees, unlike the sterile flowers of a mophead.

Essentials

At a Glance

Plant Type

Shrub

Height

36 inches

Width

36 inches

Light

Partial Sun

Zones

5, 6, 7, 8, 9

Water

Moderate; keep evenly moist

Humidity

Average to high

Lifespan

Over 20 years

Native To

Japan and Korea

Toxicity

Toxic — listed as poisonous; buds and leaves contain cyanogenic compounds

Planting

How to Grow

Plant in dappled shade or morning sun with shelter from midday heat.
Work leaf mould into the planting hole and mulch afterwards.
Keep the soil evenly moist; it wilts fast when dry.
Prune only just after flowering, cutting to a strong bud pair.
Leave the old flower heads on over winter to protect the buds.
Adjust soil pH deliberately if you want to shift the colour.

Pro Tip

It flowers on old wood, so any tidy-up after late summer removes next year's buds — prune the week the heads fade or not at all.

Keep It Thriving

Care Guide

Do

Keep the root zone cool with a generous mulch 🍂
Water before the leaves wilt, not after 💧
Prune within a few weeks of flowering ✂️
Feed acid soil with sulphur to deepen the blue 🔵

Don't

Do not prune in late winter; you cut off the flowers ❌
Do not plant it in full afternoon sun ❌
Do not let children or pets chew the buds or leaves ❌

Seasonal Care Calendar

Task	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Mulch And Protect Buds
Prune After Flowering

Watch Out For

Pests & Diseases

Common Pests

Common Diseases

In the Garden

Landscape Uses & Companions

Landscape Uses

Woodland edge and shaded border shrubSmall garden or courtyard planting where mopheads would be too largeContainer and patio specimen in part shade

Companion Plants

Japanese maple HostaJapanese forest grass EpimediumChristmas fern

Multiply

Propagation Methods

Good to Know

Common Questions

Mountain Hydrangea questions

What zones can Mountain Hydrangea grow in?

Mountain Hydrangea is hardy in USDA Zones 5–9. Inside that range it survives winter in the ground; outside it, grow it as an annual or a container plant you protect.

Is Mountain Hydrangea deer resistant?

Yes — Mountain Hydrangea is rated deer-resistant. Deer typically pass it over, though extreme hunger can override any plant's defenses.

When does Mountain Hydrangea bloom?

Mountain Hydrangea typically blooms in summer through early fall. Exact timing shifts a week or two with your zone — Sow's bloom calendar maps it to your garden.

Does Mountain Hydrangea need full sun?

Mountain Hydrangea does best in part shade.