Oakleaf hydrangea

Oakleaf hydrangea: how do you recognise it?

Habit

Broad, rounded shrub 1.5–2 m tall and often even wider, with sturdy stems.

Leaves

Large, deeply lobed like oak leaves, dark green with a felty underside.

Flowers

Cone-shaped panicles 15–25 cm long of white flowers, from July to September; turning pink as they fade.

Autumn colour

Red, purple and bronze; the leaves often hang on the shrub for a long time.

Bark

On older stems it peels away in thin, cinnamon-brown strips.

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

Why grow it?

• Interest in all four seasons: summer flowers, autumn colour, peeling bark in winter.
• One of the finest autumn colours of any shrub, often lasting into late November.
• The white panicles flower from July to September and slowly turn pink.
• Bees visit the flowers.
• Grows in sun or partial shade and needs hardly any pruning.

Oakleaf hydrangea: where does it grow best?

• Sun or partial shade; morning sun and afternoon shade give the best flowers and autumn colour.
• Humus-rich, well-drained soil: sand, loam or clay, acid to neutral. On chalky soil the leaves turn yellow.
• Moist soil: do not let it dry out, but avoid waterlogging too.
• Sheltered from cold winds and late frosts, which can damage the young shoots.
• Allow 1.5–2 m of space: it grows wider than you might think.

Light

Sun and partial shade

Soil type

Sand, loam or clay

Acidity

Acid or neutral

Moisture

Normal

Size

1.5 m tall, 2 m wide

Hardiness

Hardy (to -25 °C)

Goes well with

• Ferns: Fine green fronds beside the bold oak-shaped leaves, in the same partial shade.
• Hosta: Large leaves at its feet, in the same moist, humus-rich soil.
• Barrenwort: A low, evergreen ground cover that copes with dry shade.
• Japanese forest grass: Arching golden-green leaves as a soft edging at the front.

Oakleaf hydrangea: when and how to plant it?

Plant in March–April and October–November.

1. Plant in March–April or October–November, when the ground is neither frozen nor waterlogged.
2. Dig a hole twice as wide as the root ball and mix in leaf mould.
3. Set the plant at the same depth as it was in the pot and firm the soil well.
4. Keep 1.5–2 m away from other shrubs or a path.
5. Water in thoroughly straight away, even if it is raining.
6. Spread a mulch of leaf mould or bark around the base.

Care

Watering

Regularly in dry spells for the first two years. After that, water generously at the base in dry summers.

Feeding

In March, compost or an organic feed for acid-loving plants. Do not feed after July.

Mulching

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

Deadheading

Leave the panicles on: they dry beautifully and look decorative in winter.

Space

Choose a spot where it can spread from the start, and you will not need to prune.

Tip: Give it 1.5–2 m of space from the start, so you never need to prune and every flower bud is spared. A spot with morning sun and afternoon shade gives both plenty of flowers and the best autumn colour.

Oakleaf hydrangea: when to prune it?

Pruning months: August–September.

When: As little as possible, and only straight after flowering, in August or early September.

How:

• Remove dead, damaged or crossing stems at the base.
• Too big? After flowering, take out one or two of the oldest stems at ground level instead of shortening the whole shrub.
• If you want to remove the spent panicles, cut them off just below the flower head straight after flowering.
• Never cut back the tips in winter or spring: that is where next year’s flower buds are.

Caution: It flowers on the previous year’s wood: pruning in autumn, winter or spring removes the flower buds.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Softwood cuttings

In June: 10 cm cuttings from non-flowering shoots, lower leaves removed and large leaves cut in half, in moist cutting compost under plastic.

Layering

In summer, peg a low stem to the ground and cover it with soil. Sever and replant it after a year.

Suckers

An older shrub sometimes forms suckers around the edge. Dig them up with roots in spring.

Oakleaf hydrangea: how does it get through the winter?

Hardy to −25 °C.

• Hardy to about −25 °C: the shrub itself needs no protection in Belgium.
• Late frosts in April can damage young shoots and buds. Cover young plants with horticultural fleece on frosty nights.
• Leave the dry panicles standing: covered in hoar frost they are a winter highlight.
• In a pot: stand it against a sheltered wall and wrap the pot in hessian.

Diseases and pests

• No flowers: Pruned at the wrong time or buds killed by late frost. Prune only after flowering and choose a sheltered spot.
• Yellow leaves: Yellow leaves with green veins point to soil that is too chalky. Mulch with leaf mould and use a feed for acid-loving plants.
• Drooping leaves: A sign of drought or too much afternoon sun. Water generously at the base and mulch.
• Root rot: The shrub struggles in wet, poorly drained soil. Move it to a higher, better-drained spot.
• Aphids: On young shoots in spring. Ladybirds usually deal with them; otherwise hose them off.

Through the year

• March: Give compost or feed for acid-loving plants. Do not prune: the flower buds are at the tips.
• April: Plant. Mulch. Protect young shoots on frosty nights.
• May: Watch for aphids. Water in dry weather.
• June: The flower panicles appear. Take softwood cuttings.
• July: Flowering begins. Water in dry weather.
• August: Full flower; the panicles turn pink. Light prune after flowering if needed.
• September: Finish any pruning by early September. Let the panicles dry.
• October: Red to purple autumn colour. Plant.
• November: Plant. The leaves often hang on for a long time.
• December: Dormant. The peeling bark and dry panicles decorate the garden.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• The American naturalist William Bartram described the species in the 18th century during his travels through the south-eastern United States.
• Oakleaf hydrangea is the official state wildflower of Alabama.
• Unlike the common hydrangea, its flowers do not turn blue on acid soil: they stay white and turn pink as they fade.