Rough-leaved hydrangea

Rough-leaved hydrangea: how do you recognise it?

Habit

Loose, upright to spreading shrub 2–3 m tall and wide, with sturdy, hairy young stems.

Leaves

Large, elongated oval, 10–25 cm, matt dark green and velvety-hairy; rough above, softer beneath.

Flowers

Flat lacecaps 15–25 cm across at the stem tips, in July and August.

Colour

A centre of lilac to purple-blue flowers, ringed by white to pale pinkish-lilac sterile florets.

Leafing out

It comes into leaf late in spring; the young shoots are vulnerable to late frost.

Flowering: July–August · Plants: March–April and October–November · Pruning: March–April

Why grow it?

• Large, velvety leaves that give a shady garden an exotic, woodland feel.
• Flowers in July and August, long after most spring shrubs have finished.
• The lilac lacecaps attract bees, especially the small fertile flowers in the centre.
• Little pruning: just remove dead wood.
• A striking specimen for a sheltered corner or a woodland edge.

Rough-leaved hydrangea: where does it grow best?

• Partial or light shade, for example under tall trees; in full sun the large leaves scorch.
• Humus-rich, moisture-retentive soil: sandy, loamy or clay, acid to neutral.
• Moist soil is ideal, as long as water does not stand.
• Sheltered from strong wind, which tears the large leaves, and from cold spring winds.
• Allow 2–2.5 m of space: it grows wide and needs room to show itself off.

Light

Partial shade and shade

Soil type

Sand, loam or clay

Acidity

Acid or neutral

Moisture

Normal or wet

Size

2.5 m tall, 2.5 m wide

Hardiness

Hardy (to -20 °C)

Goes well with

• Ferns: Fine green foliage as a contrast with the large, rough leaves.
• Hosta: Calm, large leaves at its feet, in the same partial shade.
• Barrenwort: A tough ground cover for dry or moist shade beneath the shrub.
• Japanese anemone: Carries on flowering in August and September, in pink and white.
• Siberian bugloss: Small blue spring flowers before the hydrangea comes into leaf.

Rough-leaved 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 generous hole, twice as wide as the root ball, and mix in a few spadefuls of leaf mould.
3. Set the plant at the same depth as it was in the pot and firm the soil well.
4. Keep 2–2.5 m from other shrubs and at least 1 m from a wall or path.
5. Water in thoroughly straight away, even if it is raining.
6. Spread a mulch of leaf mould or wood chips around the base.

Care

Watering

Weekly in dry spells in the first year. Later on, also water generously in dry summers: the large leaves lose a lot of moisture.

Feeding

In April, a layer of compost or a little organic feed for flowering shrubs. Do not feed after July.

Mulching

A layer of leaf mould every spring keeps the soil cool and moist, as in a wood.

Spent flowers

Leave them on over winter; cut them off in spring above a healthy bud.

Space

Give it room and do not clip it into shape: its natural, loose habit is its charm.

Tip: Plant it in sheltered partial shade and in spring only remove dead wood and the old flower heads. That way it keeps its natural shape and flowers well every year.

Rough-leaved hydrangea: when to prune it?

Pruning months: March–April.

When: From late March to April, as the buds break and you can see clearly which wood is dead.

How:

• Cut dead and frosted stems back to healthy wood.
• Cut off the spent flower heads above a few healthy buds.
• Every few years, remove an old, bare stem at the base to keep the shrub young.
• Leave the other stems alone: hard pruning costs flowers.

Caution: Do not cut it back hard like a smooth hydrangea: the flowers appear at the tips of stems already on the shrub.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Softwood cuttings

In June–July: 10–15 cm cuttings from non-flowering shoots, large leaves cut in half, in moist cutting compost under plastic.

Layering

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

Rough-leaved 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 kill the young shoots; cover young plants with fleece for the night.
• A sheltered spot among other shrubs or trees protects it from cold wind.
• In the first year, a thick layer of leaf mould or fallen leaves around the base helps against hard frost.

Diseases and pests

• Frosted young shoots: Brown, limp shoots after a late frost. Cut them back to healthy wood; new shoots will follow, although it may flower less that year.
• Torn or scorched leaves: Caused by wind or strong sun. Choose a sheltered spot in partial shade.
• Drooping leaves: A sign of drought. Water generously at the base and mulch the soil.
• Aphids: On young shoots in spring. Ladybirds usually deal with them; otherwise spray them off with water.

Through the year

• March: Plant. Cut out dead stems as soon as you can recognise them.
• April: Finish pruning: remove spent flower heads and frosted wood. Add compost and mulch.
• May: Protect young leaves from late frost. Watch for aphids.
• June: Water in dry spells. Take softwood cuttings.
• July: Flowering begins. Water generously in dry spells.
• August: Full flower. Water. No more feeding.
• September: The flower heads change colour and dry.
• October: Plant. Leaf fall.
• November: Plant. Leave the spent flower heads in place.
• December: Dormant.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• The name aspera means ‘rough’ and refers to the hairy leaves, which feel rough to the touch.
• Subspecies sargentiana is named after Charles Sprague Sargent, the first director of the Arnold Arboretum in Boston.
• As in other lacecap hydrangeas, the large showy florets around the edge are sterile: they lure insects to the small fertile flowers in the centre.