White ash

White ash: how do you recognise it?

Habit

Fast-growing deciduous tree about 20 m tall and 15 m wide, with a straight trunk and an oval to round crown.

Leaves

Compound, 20–30 cm long, usually with 5–9 leaflets; dark green above, pale to whitish beneath. Yellow to purple-red in autumn.

Flowers

Small, inconspicuous flowers in April–May, before the leaves open. The tree is mostly dioecious: there are male and female trees.

Fruit

Winged seeds in hanging clusters on female trees, in autumn and winter.

Bark

Grey, with diamond-shaped furrows that deepen with age.

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

Why grow it?

• Fast growth: in a few years a sturdy tree that gives shade.
• Lovely autumn colour, from yellow to purple-red.
• Straight trunk and an oval to round crown, suitable as a specimen or in an avenue.
• Very hardy and tough, even on somewhat heavier soil.
• The strong, elastic timber is used for tool handles and sports equipment.

White ash: where does it grow best?

• Full sun for the best autumn colour and vigorous growth.
• Fresh, rich soil: sand, loam or clay, acid to chalky.
• Normally moist; tolerates temporarily wet or dry spells but not prolonged standing water.
• Give it plenty of space: 8–10 m to the next tree and at least 10 m from buildings and pipes.
• Sheltered from very strong wind while young; mature trees are reasonably storm-resistant.

Light

Sun

Soil type

Sand, loam or clay

Acidity

Not fussy

Moisture

Normal

Size

20 m tall, 15 m wide

Hardiness

Hardy (to -35 °C)

Goes well with

• Red-barked dogwood: Red stems in winter beneath the light crown.
• Hazel: Native shrub for a natural hedge at the edge of the tree.
• Snowdrop: Flowers beneath the still-bare tree, in January and February.
• Daffodil: Yellow in spring beneath the late-leafing crown.

White ash: 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. Dig a hole twice as wide as the root ball and just as deep. Loosen the sides and mix a little compost into the excavated soil.
3. Set the tree at the same depth as it stood in its pot or root ball: the root collar stays at soil level.
4. Fit a tree stake and tie the trunk loosely with a tree tie. Keep 8–10 m away from other trees.
5. Water in generously straight away, even if it is raining, so the soil settles firmly around the roots.
6. Spread a 5–8 cm layer of leaf mould or wood chips around the tree, keeping it clear of the trunk.

Care

Water

In the first two years, water generously every week in dry spells. After that it usually manages on its own.

Feeding

Usually not needed on rich soil. On poor soil, give a little compost in March.

Mulching

A layer of leaf mould or wood chips keeps the soil moist and suppresses weeds.

Support

Keep the stake for the first 2–3 years and check the tie so it does not cut into the bark.

Self-sown seedlings

Female trees can produce seedlings. Pull them out in spring before they root deeply.

Tip: Give it a sunny spot with spacious, fresh soil and plan for its full size from the start: a 20 m ash does not belong beside a house or a small border.

White ash: when to prune it?

Pruning months: February.

When: In February, in frost-free weather, while the tree is dormant. A mature tree rarely needs pruning.

How:

• Shape young trees: choose one leading shoot and remove competing tops.
• Remove dead, broken and crossing branches.
• Raise the crown gradually by cutting back low side branches.
• Leave work on large branches to a tree surgeon.

Caution: Do not cut thick branches without expert advice: large pruning wounds heal slowly.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

Sow the winged seeds outdoors in autumn. They need cold to germinate and sometimes lie dormant for one or two winters.

Grafting

Selections such as ‘Autumn Purple’ are grafted onto a seedling by the nursery. This is not easy at home.

White ash: how does it get through the winter?

Hardy to −35 °C.

• Fully hardy, down to about −35 °C: no protection needed in Belgium.
• The leaves fall early in autumn; leave them as natural mulch or take them to the compost heap.
• On young trees, check after a storm that the stake and tie are still secure.

Diseases and pests

• Ash dieback: A fungal disease that mainly affects our common ash: leaves wilt, shoots die and the crown thins. Other ashes can be affected too. Remove dead branches and keep the tree vigorous; if in doubt, ask a tree surgeon for advice.
• Leaf spot: Brown spots on the leaves and early leaf fall in wet springs. Clear away fallen leaves; the tree usually recovers by itself.
• Aphids and honeydew: Sticky leaves and black sooty mould in summer. Usually harmless; ladybirds often clear them.
• Branch breakage: Branches can break in a severe storm or under wet snow. Good formative pruning in youth prevents this.

Through the year

• February: Prune: formative pruning of young trees and dead branches.
• March: Plant. Check the stake.
• April: Flowering before the leaves. Plant.
• May: The leaves open. Water young trees in dry weather.
• June: Water young trees in dry weather.
• July: Water young trees in dry weather.
• September: Seed clusters ripen on female trees.
• October: Yellow to purple-red autumn colour. Plant.
• November: Plant. Leave the leaves or clear them away.
• December: Plant in frost-free weather.

Did you know?

• The leaves are pale underneath, hence the name white ash.
• The timber of white ash is strong and elastic and has long been used for tool handles and baseball bats, among other things.
• Ashes belong to the olive family, like olive, jasmine, lilac and forsythia.