Mountain hydrangea

Mountain hydrangea: how do you recognise it?

Habit

Compact, rounded shrub 1–1.5 m tall and as wide, with thin, upright stems.

Leaves

Narrowly oval and pointed, 5–15 cm, with a finely toothed edge; thinner and more matt than those of the mophead hydrangea.

Flowers

Flat lacecaps of 6–12 cm: small fertile flowers in the centre and a ring of large showy florets.

Colour

Blue on acid soil, pink on neutral to chalky soil. There are also white cultivars, which stay white.

Roots

Shallow and finely branched: it dries out quickly and likes a cool, moist root run.

Flowering: June–September · Plants: March–April and October–November · Pruning: March

Why grow it?

• Flowers from June into September, even in partial shade.
• Finer and more graceful than the mophead hydrangea, and better able to cope with frost.
• Compact: fits a small garden, a narrow border or a large pot.
• The small fertile flowers in the centre of the lacecaps attract bees.
• In many cultivars the flower heads, and sometimes the leaves, colour beautifully red or purple in autumn.

Mountain hydrangea: where does it grow best?

• Partial or light shade, ideally with morning sun and shade in the afternoon.
• Humus-rich, moisture-retentive soil: sandy, loamy or peaty, acid to neutral.
• Rather moist than dry: it does well in damp soil, as long as water does not stand.
• A sheltered spot protects the flower buds from late spring frosts.
• Allow 1–1.2 m per plant; in a group, 80–100 cm apart.

Light

Partial shade and shade

Soil type

Sand, loam or peat

Acidity

Acid or neutral

Moisture

Normal or wet

Size

1 m tall, 1 m wide

Hardiness

Hardy (to -20 °C)

Goes well with

• Hosta: Large, calm leaves at its feet, in the same partial shade.
• Ferns: Fresh green underplanting that likes the same moist, acid soil.
• Japanese maple: A graceful small tree for light shade above, with fine autumn colour.
• Sweet woodruff: A white-flowering ground cover in spring, before the hydrangea blooms.
• Japanese forest grass: Yellow, arching blades as a contrast in the shade.

Mountain hydrangea: when and how to plant it?

Plant in March–April and October–November.

1. Plant in March–April or October–November, when the soil is neither frozen nor waterlogged.
2. Dig a hole twice as wide as the root ball and mix in leaf mould or peat-free ericaceous compost.
3. Set the plant at the same depth as it was in the pot and firm the soil well.
4. Water in thoroughly straight away, even if it is raining.
5. Spread a mulch of leaf mould, bark or pine needles around the base to keep the soil cool and moist.

Care

Watering

Weekly in dry spells in the first year. After that, water generously at the base in dry summers: the leaves soon droop.

Feeding

In April, compost or an organic feed for hydrangeas or ericaceous plants. Do not feed after July.

Colour

For blue flowers, use rainwater and keep the soil acid; lime turns the flowers pink. White cultivars do not change colour.

Mulching

A layer of leaf mould or bark every spring keeps the soil acid, cool and moist.

Spent flowers

Leave them on over winter: they protect the flower buds below. Only cut them off in March.

In a pot

A pot of at least 40 cm with ericaceous compost; in summer, water almost daily.

Tip: In March, only cut off the spent flower heads, just above the first pair of fat buds. For blue flowers, water with rainwater: hard tap water gradually turns them pink.

Mountain hydrangea: when to prune it?

Pruning months: March.

When: In March, once the hardest frosts are over and the fat buds are easy to see.

How:

• Only cut off the spent flower heads, just above the first pair of fat, healthy buds.
• Remove dead, frosted and very thin stems at the base.
• Every few years, take one or two of the oldest stems out at ground level to keep the shrub young.
• Do not shorten the other stems: this year’s flower buds sit at their tips.

Caution: It flowers mainly on last year’s wood: hard pruning in spring costs you that year’s flowers.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Softwood cuttings

In June–July: 10 cm cuttings from non-flowering shoots, lower leaves removed, in moist cutting compost under plastic. Roots after 4–6 weeks.

Layering

In summer, bend a low stem to the ground, lightly wound the bark and peg it down under some soil. Sever and replant after a year.

Mountain hydrangea: how does it get through the winter?

Hardy to −20 °C.

• Hardy to about −20 °C: in Belgian gardens it simply stays outside.
• Late frosts in April or May can damage the young buds; cover the shrub with fleece for the night.
• Leave the spent flower heads until March: they protect the buds below.
• In a pot: stand it against a wall and wrap the pot in hessian or bubble wrap so the roots do not freeze.

Diseases and pests

• No flowers: Usually pruned too hard or buds killed by late frost. Only remove the old flower heads and protect it against spring frost.
• Yellow leaves with green veins: Chlorosis caused by chalky soil or hard tap water. Use rainwater, mulch with pine needles or bark and use an ericaceous feed.
• Drooping leaves: A sign of drought or too much afternoon sun. Water generously and mulch; move it to a shadier spot if necessary.
• Aphids: On young shoots in spring. Ladybirds usually deal with them; otherwise spray them off with water.

Through the year

• March: Cut off spent flower heads above the first pair of fat buds. Remove dead wood.
• April: Plant or move. Add compost and mulch. Cover during late frosts.
• May: Watch for aphids. Water in dry spells.
• June: Flowering begins. Take softwood cuttings.
• July: Full flower. Water generously in dry spells. No more feeding.
• August: Flowering. Water. Layer a low stem.
• September: Last flowers; the flower heads take on lovely colours.
• October: Plant. Autumn colour in leaves and flower heads.
• November: Plant. Leave the spent flower heads in place.
• December: Dormant. Protect pots from hard frost.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• The name serrata means ‘saw-toothed’ and refers to the finely toothed leaf edge.
• Whether the flowers turn blue or pink depends on aluminium in the soil: the plant can only take it up from acid soil, and the flowers then turn blue.
• The large showy florets around the edge of the lacecap are sterile: they lure insects to the small fertile flowers in the centre.