Tree of heaven

Tree of heaven: how do you recognise it?

Habit

Fast-growing tree of 15–25 m with an open crown and thick, sparsely branched twigs; forms stands through root suckers.

Leaf

Alternate, pinnate, 40–90 cm long with 13–41 leaflets. These are untoothed apart from 1–3 coarse teeth near the base, with a small gland beneath. Stinks when crushed.

Bark

Smooth, grey with pale vertical stripes.

Flower

Large panicles of small yellow-green flowers in June–July, mostly on separate male and female trees; the male flowers smell unpleasant.

Fruit

Clusters of twisted winged fruits that turn red to brown.

Difference from walnut

Walnut has fewer (5–9), larger leaflets without teeth, and a pleasant smell.

Difference from ash

Ash has opposite leaves with toothed leaflets.

Flowering: June–July

Identify by feature: Pinnate leaves · Winged seeds

Looks like it, but isn’t

• Walnut Juglans regia: fewer (5–9), larger leaflets without teeth, and a pleasant smell. Difference from walnut
• Ash Fraxinus excelsior: opposite leaves with toothed leaflets. Difference from ash

Why grow it?

• Why not to plant it: it is on the EU list of invasive species; planting, growing, selling and giving it away are banned.
• It spreads through root suckers and thousands of seeds and crowds out native plants.
• Its roots and seedlings force their way into joints, walls and paving and damage them.
• Recognise it early: a seedling is still easy to pull up, while a large tree is costly to deal with.

Tree of heaven: where does it grow best?

• Grows in full sun on any soil, even on rubble, gravel and between paving.
• Tolerates drought, heat and air pollution: that is why it thrives so well in towns and cities.
• You find it mainly in towns and along railways and roads; from there it spreads into gardens, verges and woodland edges.

Light

Full sun

Legal basis

Any garden soil

Moisture

Dry

Size

25 m tall, 12 m wide

Hardiness

Throughout Belgium, no protection needed

Goes well with

• Rowan: A native tree with equally graceful pinnate leaves, but small and a feast for birds.
• Silver birch: Grows just as fast and easily on poor soil, but is native.
• Field maple: A native tree that tolerates drought and urban soil.
• Small-leaved lime: A native shade tree that also flowers for bees.

Good and bad companions

Goes well with

• Tolerate the shade under this tree: oregon grape, rhododendron, oleaster, japanese skimmia, garden privet, camellia, laurustinus, box-leaved honeysuckle

Tree of heaven: when and how to plant it?

1. Don’t plant it: it is banned, even if someone gives you one. Don’t let seedlings grow on in your garden either.
2. Looking for a tree with graceful pinnate leaves? Choose rowan. For a fast, airy tree on poor soil: silver birch. For shade: field maple or small-leaved lime.
3. Pull up seedlings as soon as you see them, roots and all, preferably after rain when the soil is soft.
4. Is there a large tree of heaven in or next to your garden? Don’t fell it yourself; have it dealt with by a specialist contractor.

Care

Seedlings

Pull them up in their first year with the whole root; broken-off roots sprout again.

Root suckers

Cut or mow suckers again and again, several times a year and for years on end, until the roots are exhausted.

Female trees

Trees with red fruit clusters seed themselves most: deal with those first.

Reporting

Report trees of heaven to your local council or on waarnemingen.be: that way control can be targeted.

Tip: Not sure whether it is tree of heaven or walnut? Crush a leaflet: tree of heaven stinks, walnut smells spicy. Also look for the 1–3 coarse teeth at the base of each leaflet.

Tree of heaven: when to prune it?

When: Don’t prune; have it removed.

How:

• Felling or pruning triggers dozens of root suckers.
• Pull up young seedlings, roots and all; have large trees dealt with by a specialist: usually the tree is first killed off (ring-barking or a trunk treatment) and only felled afterwards.
• Report the species to your local council or on waarnemingen.be.

Caution: Wear gloves and long sleeves: the sap can irritate the skin.

Pruning calendar and basic rules

Propagation

Don’t propagate

Propagating, growing and giving it away are banned: it is on the EU list of invasive species.

How it spreads

Every year female trees produce large numbers of winged seeds that blow a long way; it also suckers far from the trunk, especially after felling or pruning.

Tree of heaven: how does it get through the winter?

Hardy throughout Belgium: no protection needed.

• Fully hardy.
• In winter you recognise it by its thick, bare twigs with large, heart-shaped leaf scars, and by fruit clusters that often hang on until spring.

Diseases and pests

• Suckers after felling: A felled tree of heaven sprouts dozens of shoots all around. Kill it off before felling, and keep cutting new suckers for years.
• Seedlings in joints and walls: Within a few years seedlings grow into trees that damage masonry and paving. Pull them up young, with the whole root.
• Skin irritation: The sap and crushed leaves can irritate the skin. Wear gloves and long sleeves.
• Smell: Crushed leaves and male flowers smell unpleasant. At least it helps with identification.

Through the year

• May: Leaves open: look for seedlings and suckers with the pinnate, smelly leaves and pull them up.
• June: Flowering: male trees smell unpleasant, female trees set seed.
• July: Cut or mow suckers again.
• August: Fruit clusters turn red: these are female trees, deal with them first.
• September: Pull up this year’s seedlings before they root firmly.
• October: Seeds blow away; report trees to your local council or on waarnemingen.be.

Did you know?

• An invasive non-native species from China, on the EU list of invasive alien species.
• Young trees and root suckers often grow more than a metre a year.
• The name Ailanthus comes from a Moluccan tree name that is thought to mean ‘tree of heaven’.
• The name Ailanthus comes from ailanto, a word from the Moluccan island of Ambon thought to mean ‘tree of heaven’; altissima means ‘very tall’.
• In the 19th century it was planted in Europe to rear the ailanthus silkmoth, a silkworm that feeds on its leaves, in the hope of producing silk.