Chestnut-leaved oak

Chestnut-leaved oak: how do you recognise it?

Habit

Broad, rounded crown on a sturdy trunk; up to 25 m tall and 15–18 m wide.

Leaves

Oblong, 10–20 cm, with sharp, forward-pointing teeth like the sweet chestnut; glossy dark green, paler underneath.

Flowers

Hanging, yellowish catkins in May, as the leaves unfold. Wind-pollinated.

Fruit

Acorns in a bristly, scaly cup; they only ripen in the second year after flowering.

Bark

Grey to dark grey, deeply furrowed on older trees.

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

Why grow it?

• An imposing shade tree that grows remarkably fast for an oak.
• Glossy, dark green foliage that turns yellow-brown in autumn.
• The acorns and the large crown provide food and shelter for birds and insects.
• It lives to a great age: a tree for generations that is a real feature in a park or on a large estate.
• Grows on sandy, loamy and clay soil, acid as well as chalky.

Chestnut-leaved oak: where does it grow best?

• Full sun is best: it grows fast and forms the finest crown in the sun.
• Ordinary garden soil: sand, loam or clay, acid to chalky; deep and moisture-retentive is ideal.
• Moderately moist soil, but not waterlogged. Once established it copes fairly well with a dry summer.
• Allow at least 15–18 m of space, well away from buildings, pipes and boundaries: crown and roots become large.

Light

Sun

Soil type

Sand, loam or clay

Acidity

Not fussy

Moisture

Normal

Size

25 m tall, 18 m wide

Hardiness

Hardy (to -23 °C)

Goes well with

• Bluebell: Flowers in April–May, before the oak is in leaf, and enjoys the shade beneath.
• Wood anemone: A low carpet of spring flowers under deciduous trees.
• Holly: Evergreen understorey that gives the tree a green backdrop in winter.
• Hazel: A native shrub for a natural woodland edge.
• Male fern: A tough fern that tolerates dry shade under the crown.

Chestnut-leaved oak: when and how to plant it?

Plant in March–April and October–December.

1. Plant in March–April or from October to December, when the soil is neither frozen nor waterlogged.
2. Choose the spot with care: keep at least 15 m from houses and other large trees.
3. Dig a hole two to three times as wide as the root ball, but no deeper. Loosen the sides so the roots can spread easily.
4. Plant at the same depth as in the nursery and backfill with the soil you dug out, without fresh manure. For a standard tree, add a stake and tie loosely.
5. Water in at once with 20–30 litres.
6. Spread a mulch ring about 1 m wide of wood chips or leaf mould, keeping it clear of the trunk.

Care

Water

For the first 2–3 summers give 20–30 litres a week in dry spells, deeply and not too often. After that it usually looks after itself.

Feeding

Usually not needed. On poor sandy soil you can add a thin layer of compost in spring.

Mulching

Keep a grass-free circle around young trees: grass competes for water and nutrients.

Support

A standard tree needs a stake for 2–3 years. Remove it afterwards so the trunk grows strong.

Autumn leaves

The tough oak leaves rot down slowly. Leave them under shrubs or make leaf mould.

Tip: Plant a young tree of 2–3 m rather than a large one: it roots faster and then grows more vigorously. Water it deeply and regularly for the first three summers.

Chestnut-leaved oak: when to prune it?

Pruning months: December–February.

When: Only when needed, during dormancy from December to February, in dry, frost-free weather.

How:

• In the early years, build up a single leader and a balanced crown: remove competing tops and crossing branches.
• Take out dead or broken branches; cut just outside the branch collar, never into the collar itself.
• Thin branches up to 3–4 cm you can saw yourself; for thick branches and large trees, call in a tree surgeon.

Caution: Avoid pruning an oak in spring or summer: fresh wounds are more prone to infection then.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

Sow fresh acorns in October–November where they are to grow or in deep pots, as the taproot soon gets long. They germinate in spring. Acorns dry out quickly: do not store them. Seedlings can differ from the parent tree.

Grafting

Selections such as ‘Green Spire’ are grafted by nurseries. This is not a job for the gardener: buy such a tree from a nursery.

Chestnut-leaved oak: how does it get through the winter?

Hardy to −23 °C.

• Hardy to about −23 °C: no problem in Belgian winters.
• On young trees, a layer of mulch protects the roots during hard frosts.
• Protect the trunk of young trees from game, rabbits and the mower with a tree guard.

Diseases and pests

• Oak processionary moth: Nests of hairy caterpillars on the trunk and branches from May to July. The stinging hairs can cause severe skin irritation. Do not touch the nests and have them removed by an approved contractor or the council. Blue tits and other insect-eating birds help: put up nest boxes.
• Powdery mildew: White powder on young leaves, especially in late summer. Usually harmless on a mature tree; clear fallen leaves and avoid nitrogen-rich fertiliser.
• Galls: Balls or lumps on leaves and twigs, caused by gall wasps. They are harmless to the tree and need no action.
• Drought stress: Limp or yellowing leaves and early leaf fall on young trees in a dry summer. Water deeply for the first few years and keep the mulch in place.

Through the year

• January: Remove dead branches in dry, frost-free weather.
• February: Last chance to prune. Check stakes and ties.
• March: Plant once the soil has thawed and is not too wet. Water in well.
• April: Plant. Mulch. The tree comes into leaf.
• May: Yellow catkins. Watch for oak processionary moth nests.
• June: Water young trees in dry weather. Have processionary nests removed.
• July: Water young trees deeply in dry weather.
• August: Water young trees deeply in dry weather.
• October: Acorns fall; sow fresh acorns. Planting can start again.
• November: Plant. Collect fallen leaves for leaf mould.
• December: Plant. Pruning of dead branches possible.

Good for wildlife

Birds

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

Did you know?

• It grows naturally in the mountain forests around the Caspian Sea, in the Caucasus and northern Iran.
• The leaves look so like those of the sweet chestnut that the name refers to it: castaneifolia means ‘with chestnut leaves’.
• The acorns only ripen in the second year after flowering.