Smooth hydrangea

Smooth hydrangea: how do you recognise it?

Habit

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

Leaves

Broadly oval, 8–15 cm, with a toothed edge, opposite; fresh green, yellow in autumn.

Flowers

Large domed or flat heads at the tips of the new shoots, from June to September.

Colour

Greenish white at first, then pure white, later green again. There are pink varieties too.

Roots

Shallow and branching: it dries out quickly, but is easy to move.

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

Why grow it?

• Flowers for three months, even in partial shade, where few other shrubs bloom so freely.
• Fully hardy: no frosted buds, because it flowers on this year’s stems.
• The faded heads stay attractive and look wonderful in winter when covered in frost.
• Ideal as a cut flower and for drying for a bouquet.
• Little work: one prune a year is enough.

Smooth hydrangea: where does it grow best?

• Partial or light shade is ideal; full sun only if the soil stays moist.
• Humus-rich, moisture-retentive soil: sand, loam or clay, acid to neutral.
• Sheltered from strong wind, as the heavy flower heads bend or snap.
• Allow 1–1.2 m per plant; in a group or as a low hedge, 80 cm apart.

Light

Partial shade and shade

Soil type

Sand, loam or clay

Acidity

Acid or neutral

Moisture

Normal or wet

Size

1.5 m tall, 1.5 m wide

Hardiness

Hardy (to -28 °C)

Goes well with

• Hosta: Large leaves at its feet, in the same partial shade.
• Ferns: Fresh green underplanting for a shady border.
• Astilbe: Plumes in pink and red beside the white globes.
• Lady’s mantle: A soft yellow edging at the front of the border.
• Japanese anemone: Flowers on into September, when the hydrangea turns green.

Smooth 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 not frozen or waterlogged.
2. Dig a hole twice as wide as the root ball and mix in a few spadefuls of 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 or wood chips around the base.

Care

Water

In the first year, weekly in dry spells. After that, water generously in dry summers, in the morning and at the base: the leaves soon droop.

Feeding

In April, compost or an organic feed for flowering shrubs. Do not feed after July.

Mulching

A layer of leaf mould in spring keeps the soil cool and moist.

Support

A plant support or ring around the shrub stops the heavy heads flopping after a downpour.

Faded flowers

Leave them until the March prune: they look good in winter and protect the buds.

Tip: Don’t prune too short if the heads flop every year: stems of 40–50 cm are sturdier. The variety ‘Strong Annabelle’ naturally has stronger stems.

Smooth hydrangea: when to prune it?

Pruning months: March.

When: From late February to late March, before the new shoots start to grow.

How:

• Cut all stems back to 20–30 cm above the ground, just above a pair of buds.
• If you leave them 40–50 cm long, the stems will be sturdier and the flowers will bend less.
• Remove thin, weak and dead stems right down at the base.
• Taking out a few of the oldest stems at ground level every few years keeps the shrub young.

Caution: It flowers on new wood: hard pruning in spring costs no flowers, pruning in summer does.

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 form after 4–6 weeks.

Division

In spring, slice off a rooted piece from the edge of the clump with a spade and plant it elsewhere.

Layering

In summer, bend a low branch down into the soil and pin it in place; sever it after a year.

Smooth hydrangea: how does it get through the winter?

Hardy to −28 °C.

• Fully hardy, to about −28 °C: no protection is needed, even in severe Belgian winters.
• Leave the faded heads until March: covered in frost, they are a winter feature.
• In a pot: stand it against a wall and wrap the pot in hessian, so the roots do not freeze.

Diseases and pests

• Flopping flowers: After rain the heads bend over. A plant support, less severe pruning and a sheltered spot all help.
• Drooping leaves: A sign of drought: water generously. In too sunny a spot, it happens every summer.
• Powdery mildew: White powder on the leaves, especially in dry weather. Water, give the plant space and cut off affected leaves.
• Aphids: On young shoots in May. Ladybirds usually clear them up; otherwise spray them off with water.

Through the year

• March: Prune to 20–30 cm above the ground. Give compost or feed.
• April: Plant or move. Mulch.
• May: Put a plant support in place. Watch out for aphids.
• June: First flowers. Take softwood cuttings.
• July: Full bloom. Water in dry spells. Cut flowers for a vase.
• August: In flower. Water in dry spells.
• September: The heads turn green again. Pick them for drying.
• October: Plant. Yellow autumn leaves.
• November: Plant. Leave the faded heads standing.
• December: Resting. The dry heads decorate the garden.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• Unlike the common hydrangea, this one does not turn blue on acid soil: the flowers stay white.
• ‘Annabelle’ was found growing wild around 1910 in Illinois, near the small town of Anna, after which it is named.
• Dried flower heads keep their shape and colour for years in a dried arrangement.