White oak

White oak: how do you recognise it?

Habit

Large, slow-growing deciduous tree of about 20 m tall and 18 m wide, with a broad, rounded crown and strong, horizontal branches.

Leaves

10–20 cm, with 7–9 rounded lobes; pinkish-silver on opening, green in summer, purple-red to wine-red in autumn.

Flowers

Hanging male catkins in May, at the same time as the leaves. The small female flowers are inconspicuous.

Fruit

Acorns of 2–3 cm in a shallow cup, ripe within one year; they fall in October.

Bark

Pale grey and flaky; on older trees in large plates and shallowly fissured.

Roots

A deep taproot: move it young and damage the roots as little as possible.

Flowering: May · Plants: March–April and October–December

Why grow it?

• A majestic, long-lived tree with a broad crown and plenty of summer shade.
• Superb purple-red to wine-red autumn colour, and young trees often keep their brown leaves into winter.
• Valuable for wildlife: the acorns feed birds such as jays and pigeons and mammals such as squirrels and mice.
• Pale bark and rounded leaf lobes give it a calm, handsome look in every season.
• Tough and low-maintenance: it needs no pruning and little care.

White oak: where does it grow best?

• Full sun; in shade it grows slowly and stays thin.
• Deep, well-drained sandy or loamy soil, acid to neutral; chalky soil causes chlorosis and poor growth.
• Normal moisture; it tolerates temporary drought once established, but not permanently wet ground.
• Allow 15–20 m of free space; do not plant it close to houses, pipes or boundaries.

Light

Sun

Soil type

Sand or loam

Acidity

Acid or neutral

Moisture

Normal

Size

20 m tall, 18 m wide

Hardiness

Hardy (to -35 °C)

Goes well with

• Holly: Evergreen shrub with red berries that complements the deciduous oak in winter.
• Rhododendron: An evergreen underplanting that flowers in May and likes the same acid soil.
• Bluebell: A blue carpet in spring under the still-bare crown.
• Ferns: Fresh, green underplanting in the shade at the foot of the tree.

White oak: when and how to plant it?

Plant in March–April and October–December.

1. Plant in March–April or in October–December, as long as the soil is neither frozen nor waterlogged. Preferably choose a young tree of 1–2 m.
2. Dig a hole two to three times as wide as the rootball and just as deep. Loosen the sides and bottom with the spade so the taproot can go deeper.
3. Set the tree at the same depth as it stood in the nursery; the root collar should be level with the soil.
4. Backfill, firm lightly, tie the trunk to a stake and give it a generous watering.
5. Spread a layer of acid leaf mould or bark around the base, not against the trunk.

Care

Water

In the first three summers, water generously once a week in dry weather. After that rain is usually enough.

Feeding

Not needed. Rich fertiliser gives soft growth; a layer of leaf mould in spring is enough.

Mulching

A layer of leaf mould or bark keeps the soil acid, cool and moist. Keep it away from the trunk.

Stake

A stake stays for 2–3 years; check that the tie is not cutting into the trunk.

Oak processionary moth

Check the trunk and thick branches for nests from May to July. Do not touch them and have them removed by an approved firm.

Tip: Plant it young, on acid to neutral soil and with plenty of room: it quickly forms a deep taproot and dislikes being moved. Patience is rewarded with a tree that can last for centuries.

White oak: when to prune it?

When: It normally needs no pruning. Dead or damaged branches are best removed in winter, while it is dormant.

How:

• Young tree: in the first years, prune only to form a strong trunk and a balanced crown.
• Remove dead, broken and crossing branches back to the branch collar.
• Keep one continuous leader and remove low branches only when the tree is older.

Caution: Do not remove large branches without good reason: big wounds close slowly and let fungi in.

Pruning calendar and basic rules

Propagation

Seed

Fresh acorns germinate quickly and must not dry out: sow them in October–November in deep pots or straight into their final spot, and protect them from mice and squirrels. Seedlings grow slowly at first.

Buying

A young nursery tree of 1–2 m settles in most easily and saves you years of waiting.

White oak: how does it get through the winter?

Hardy to −35 °C.

• Fully hardy, to about −35 °C: no protection is needed in Flanders.
• Young trees often keep their brown, dry leaves until spring: this is normal.
• A tree of this size does not belong in a pot: plant it in open ground only.

Diseases and pests

• Lime-induced chlorosis: Leaves turn yellow with green veins on chalky soil. Plant it only on acid to neutral soil; correcting it later is difficult.
• Oak processionary moth: Nests with stinging hairs on the trunk and thick branches from May to July. Do not touch them and have them removed by an approved firm or the council.
• Powdery mildew: White powder on young leaves in summer. Usually harmless for a healthy tree.
• Galls: Balls or lumps on leaves and twigs caused by gall wasps. They are harmless and need no control.

Through the year

• March: Plant. Check the stake.
• April: Plant. The leaves open pinkish-silver.
• May: Flowering with catkins. Water young trees in dry weather. Watch for oak processionary moth.
• June: Water in dry weather. Watch for oak processionary moth.
• July: Water young trees.
• August: Water during prolonged drought.
• September: The acorns ripen.
• October: Plant. Purple-red autumn colour. Collect and sow acorns.
• November: Plant. Leave fallen leaves as mulch.
• December: Plant. Remove dead branches.

Good for wildlife

Birds

Berries, seeds or insects as food, or a place to nest.

Did you know?

• The wood of the white oak is dense and watertight and is used to make barrels for wine and whisky.
• The ‘Charter Oak’ in Hartford, Connecticut, a white oak, was famous and fell in a storm in 1856.
• Old specimens can live for several centuries.