Hydrangea

Hydrangea: how do you recognise it?

Habit

Rounded, dense shrub of 1–2 m with thick stems from the base.

Leaf

Opposite, oval, 10–20 cm, coarsely toothed and glossy.

Bark

Thick, light brown stems.

Flower

Large heads in pink, blue or white, June–September: blue on acid soil, pink on chalky soil. Mopheads have round heads, lacecaps flat heads with small flowers in the centre.

Fruit

Small capsules.

Difference from panicled hydrangea

Panicled hydrangea (Hydrangea paniculata) has cone-shaped white panicles and flowers on new wood.

Flowering: June–September · Pruning: March–April

Identify by feature: Purple or blue flowers

Looks like it, but isn’t

• Panicle hydrangea (Hydrangea paniculata): cone-shaped white panicles; flowers on new wood.

Why grow it?

• Weeks of flowers, from June into September.
• One of the few large flowering shrubs for partial shade.
• The flowers dry beautifully and keep their colour for a long time.
• Lacecaps also attract insects with their small, fertile flowers.

Hydrangea: where does it grow best?

• Partial shade is ideal: morning sun is fine, but fierce midday sun scorches leaves and flowers.
• Moist, humus-rich soil that never dries out.
• On acid soil, coloured varieties flower blue; on chalky soil, pink.
• A sheltered spot, out of the cold east wind, protects the flower buds from late frost.

Light

Partial shade

Legal basis

Any garden soil

Moisture

Moist to wet

Size

2 m tall, 1.5 m wide

Hardiness

Throughout Belgium, no protection needed

Goes well with

• Panicled hydrangea: Flowers later, on new wood, and tolerates more sun.
• Climbing hydrangea: For the shady wall behind, with white flower heads in June.
• Japanese maple: Likes the same partial shade and moist soil, with fine leaves and autumn colour.
• Ferns: Delicate greenery for the shady base.

Good and bad companions

Goes well with

• Suits the woodland edge or the light shade of: ginkgo, box elder, ash, honey locust, field maple, silver maple

Hydrangea: when and how to plant it?

1. Plant in spring or early autumn, root-balled or from a pot.
2. Dig a wide planting hole and mix in compost or leaf mould.
3. Plant at the same depth as in the pot and firm the soil.
4. Water well straight away and keep the soil moist in the first year; a mulch helps.

Care

Watering

Generously in dry spells, ideally with rainwater. Leaves that droop on a hot afternoon often recover in the evening; if they stay limp, water.

Feeding

In spring, a little compost or a hydrangea feed; not too much nitrogen.

Blue colour

For blue flowers: water with rainwater and, if you like, add a product containing aluminium sulphate. On chalky soil blue is hardly achievable: choose a pink or white variety there.

Old flowers

Leave the faded heads on over winter: they protect the buds below from frost.

Tip: Wait to pick flowers for drying until late summer, when they feel slightly papery: then they dry beautifully and keep their colour.

Hydrangea: when to prune it?

Pruning months: March–April.

When: In March–April.

How:

• Only cut off the old flowers to just above the first pair of fat buds.
• Saw a few old, thin or dead stems off at the base; this keeps the shrub young.
• Panicled hydrangeas and the hydrangea ‘Annabelle’ (Hydrangea arborescens) flower on new wood: these you can cut back hard in March.

Caution: Don’t prune a bigleaf hydrangea any harder: it flowers on last year’s wood, and if you shorten every stem, you cut off the flowers.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Cuttings

In June–August, take 10–15 cm tip cuttings from non-flowering shoots, remove the lower leaves and put them in moist cutting compost; they root within a few weeks.

Layering

In summer, bend a low stem down to the ground, cover it with soil and sever it the following spring.

Hydrangea: how does it get through the winter?

Hardy throughout Belgium: no protection needed.

• Hardy, but late frost can kill the flower buds at the stem tips: it then flowers little that summer.
• Leave the old flowers on until spring and cover young plants with horticultural fleece in severe frost.

Diseases and pests

• No flowers: Usually caused by pruning too hard or frozen buds. Only cut off the old flowers and protect the shrub from late frost.
• Scorched or limp leaves: Too much sun or too dry. Water, mulch the soil, or move it to partial shade.
• Scale insects: White, woolly egg sacs on the stems and under the leaves in early summer. Wipe them off or cut away affected parts.
• Yellow leaves with green veins: Chlorosis on chalky soil. Add compost or leaf mould and water with rainwater.

Through the year

• March: Pruning: cut old flowers back to just above the first pair of fat buds.
• April: Last pruning; add compost.
• May: Planting; watch out for late night frost.
• June: Flowering begins; water in dry spells.
• July: Full flower; take tip cuttings.
• August: Keep watering; pick flowers for drying.
• September: Flowering ends; the heads turn green or rusty brown.
• November: Leave the old flowers on against frost.

What can you use it for?

Garden and landscape

Summer-flowering shrub for partial shade and moist soil; lovely as a dried flower.

Caution: Mildly poisonous if eaten.

Did you know?

• The flower colour gives your soil away: aluminium in acid soil turns them blue.
• The large, coloured ‘petals’ are actually the sepals of sterile flowers; the real, fertile flowers are tiny.
• The name Hydrangea comes from Greek and means ‘water vessel’, after the cup-shaped seed capsules; fitting for such a thirsty plant.
• Hydrangea comes from the Greek hydor (water) and angeion (vessel), after the small, cup-shaped seed capsules.
• The German physician Philipp Franz von Siebold, who worked for the Dutch in Japan, named a hydrangea ‘Otaksa’ after his Japanese partner, Otaki-san.