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Mountain hydrangea

Hydrangea serrata · Hydrangeaceae

Mountain hydrangea (Hydrangea serrata) in flower
Photo: Schorle, via Wikimedia Commons (CC BY-SA 4.0)

A smaller, finer relative of the bigleaf hydrangea, with flat, lacecap flowers: a centre of tiny fertile flowers ringed by showy ones, blue in acid soil and pink in alkaline.

Size
3½ ft tall, 4 ft wide
Zones
6 to 9
Light
Part sun to part shade
Flowers
Late June to mid August
Pets
Toxic (mild)
Job in a bed
Anchor

A bed built around mountain hydrangea

The planner designed this bed around mountain hydrangea when this page was made: a 16 × 8 ft (4.9 × 2.4 m) English border in zone 6, part sun. It chose the other plants from the 708 that suit those conditions, and says below why mountain hydrangea stands where it does.

A 16 × 8 ft (4.9 × 2.4 m) bed at eye level in mid July: Mountain hydrangea, Green-and-gold, Coral bells 'Firefly', White mugwort, Joe Pye weed 'Little Joe', Bowles' golden sedge, Asiatic lily, Easter lily, Camassia.
A 16 × 8 ft (4.9 × 2.4 m) English border in zone 6, part sun, seen from the path in mid July.
4. White mugwort44. White mugwort44. White mugwort45. Joe Pye weed 'Little Joe'55. Joe Pye weed 'Little Joe'55. Joe Pye weed 'Little Joe'51. Mountain hydrangea13. Coral bells 'Firefly'33. Coral bells 'Firefly'33. Coral bells 'Firefly'32. Green-and-gold22. Green-and-gold22. Green-and-gold23. Coral bells 'Firefly'33. Coral bells 'Firefly'33. Coral bells 'Firefly'33. Coral bells 'Firefly'33. Coral bells 'Firefly'32. Green-and-gold22. Green-and-gold22. Green-and-gold22. Green-and-gold22. Green-and-gold23. Coral bells 'Firefly'33. Coral bells 'Firefly'33. Coral bells 'Firefly'33. Coral bells 'Firefly'33. Coral bells 'Firefly'35. Joe Pye weed 'Little Joe'54. White mugwort47. Asiatic lily77. Asiatic lily77. Asiatic lily78. Easter lily88. Easter lily88. Easter lily89. Camassia99. Camassia99. Camassia92. Green-and-gold22. Green-and-gold22. Green-and-gold26. Bowles' golden sedge66. Bowles' golden sedge66. Bowles' golden sedge62. Green-and-gold22. Green-and-gold22. Green-and-gold22. Green-and-gold22. Green-and-gold22. Green-and-gold22. Green-and-gold22. Green-and-gold22. Green-and-gold22. Green-and-gold22. Green-and-gold27. Asiatic lily79. Camassia99. Camassia98. Easter lily8
From above, to scale. Each circle is one plant, as wide as the room it needs.

The plants

  1. 1 Mountain hydrangea × 1, blue
  2. 2 Green-and-gold × 22, yellow
  3. 3 Coral bells 'Firefly' × 13, red
  4. 4 White mugwort × 4, cream
  5. 5 Joe Pye weed 'Little Joe' × 4, pink
  6. 6 Bowles' golden sedge × 3, chartreuse leaves
  7. 7 Asiatic lily × 4, orange
  8. 8 Easter lily × 4, white
  9. 9 Camassia × 5, blue

Why this plant

  • The only dense clusters. The others are daisies, airy sprays, plumes and others. Shape reads at a distance, where colours blur.
  • Part of the bed's structure. Shrubs and grasses keep their shape when the perennials die down. So does Bowles' golden sedge.

Why here

  • At the back. At 3½ ft it is seen over green-and-gold (6 in) in front of it, and has nothing behind it to hide.
  • A step in the back row. Next to Joe Pye weed 'Little Joe' (4 ft) and white mugwort (5 ft): no two neighbours there are the same height, so the back steps up and down like a skyline.
  • One plant, alone. A shrub is seen as an object, and needs clear ground around it.

Why now

  • In flower for 9 weeks. From late June to mid August.
  • Part of the bed's peak. With coral bells 'Firefly', Asiatic lily and Easter lily in late June: 4 kinds at once. No week has more.

Planned as an English border: 6 of the 7 groups (86%) are drifts, longer along the bed than they are deep. Green-and-gold is the plant there is most of: 22 of the 60. The flowering is at its height from late June, with 4 kinds out together.

The planner's own design check: 11 Excellent, 6 Good.

Open this bed in the planner Change its size, the sun or the style, move plants about, or swap one for another.

Where mountain hydrangea goes in a border

At 3½ ft it belongs at the back of a bed. In the planner's ten height classes it is moderately tall (3 to 4 ft).

Its job: anchor. A shrub that gives the bed permanent structure. Planted singly, as soon as the front edge is laid; everything else is arranged around it.

More refined than the mopheads, and its buds survive late frosts better. The lacecaps suit a woodland setting where round mopheads would look too heavy.

  • Delicate lacecap flowers in part shade
  • Woodland gardens
  • Small gardens

What to plant with mountain hydrangea

Plants recorded as good partners for it, and what each pairing does:

  • Hosta: its green leaves are a setting for the flowers, before and after; bold leaves against its medium ones; spires rising out of its mound.
  • Astilbe: in flower together for five weeks, from late June; low enough (24 in) to stand in front of it; happy in the same moist soil.
  • Japanese painted fern: its silver leaves are a setting for the flowers, before and after; low enough (18 in) to stand in front of it; happy in the same moist soil.

Questions about mountain hydrangea

Does mountain hydrangea need sun or shade?

Mountain hydrangea grows in part sun (4 to 6 hours of sun, including some afternoon sun) and part shade (2 to 4 hours of sun, mostly in the morning).

It wants soil that stays evenly moist, rich in organic matter, and plenty of water.

What zones does mountain hydrangea grow in?

USDA zones 6 to 9. It is hardy to zone 6, which means it survives winter nights down to about 0 °F (−18 °C).

Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.

When does mountain hydrangea flower in my zone?

In zone 5 it flowers late June to mid August. As a summer flower it moves about half a week for every zone: earlier where it is warmer.

Roughly when mountain hydrangea is in flower
Zone 6Late June to mid August
Zone 7Mid June to early August
Zone 8Mid June to early August
Zone 9Early June to early August

Worked out from Hopkins' bioclimatic law: spring arrives about four days later for each degree of latitude north, and one zone is roughly two degrees. A warm spring or a cold one moves any garden two weeks either way.

How far apart should mountain hydrangea be planted?

3½ ft (100 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 4 ft (120 cm), so a group knits into one patch.

It grows 3½ ft (100 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.

How many mountain hydrangea plants do I need?

At 3½ ft apart, set out in staggered rows:

  • 1 to fill 10 square feet (about 1 m²)
  • 4 for a single row 10 ft (3 m) long
  • 3 to fill a 4 × 8 ft bed on its own

In a mixed border, plant it as one, planted singly: it is the bed's structure, and everything else is arranged around it.

In the bed above, the planner used one in one group.

Is mountain hydrangea poisonous to dogs and cats?

Yes: mild toxicity to people, dogs, cats and horses. Leaves and buds can cause vomiting and diarrhoea if eaten.

Rated from NC State Extension. Where references disagree, the more cautious rating is used.

Do deer eat mountain hydrangea?

They may. NC State does not list it as resistant to deer or rabbits. Where they visit, protect it, or plant it among ones they avoid.

What flowers after mountain hydrangea?

Mountain hydrangea is over by mid August. These start as it finishes and carry the same spot on, so it never goes flat:

  • Japanese anemone: from mid August to early October, 3 ft tall.
  • Lilyturf: from early August to mid September, 16 in tall, to stand in front of it and cover its fading stems.
  • Blue mistflower: from late August to mid October, 2½ ft tall, to stand in front of it and cover its fading stems.

What does mountain hydrangea look like in winter?

Mountain hydrangea drops its leaves and stands as bare branches. That is when to see its shape, and to prune it if it needs pruning.

Is mountain hydrangea good for bees and butterflies?

Mountain hydrangea is visited by bees.

More Hydrangea

In these guides

Zone guides: Zone 6 · Zone 7 · Zone 8 · Zone 9

In flower in: June · July · August

Every fact on record

Type
Shrub
Size
3½ ft (100 cm) tall, 4 ft (120 cm) wide
Plant
3½ ft (100 cm) apart
Height class
Moderately tall (3 to 4 ft)
Place in the bed
Back
Flowers
Late June to mid August; dense clusters; blue, pink, white
Leaves
Medium texture, deciduous; green
Shape
Rounded, clumping
Hardy in
USDA zones 6 to 9
Light
Part sun, part shade
Soil
Rich, evenly moist
Water
High
Feeding
Moderate, in spring
Family
Hydrangeaceae
Comes from
Japan, Korea
Attracts
Bees

Checked against NC State Extension. Flowering times are for zone 5: later in colder zones, earlier in warmer ones. Toxicity and spread information is a general gardening guide, not veterinary or medical advice, and invasive status varies by region. If a person or pet eats a plant, contact poison control or a vet. Check your local invasive species list before planting anything with a spread warning.