Sweetgum

Sweetgum: how do you recognise it?

Habit

Tree of 20–30 m with a straight trunk and a crown that is conical at first, later oval.

Leaf

Alternate, star-shaped with 5–7 pointed, finely toothed lobes, glossy. Smells resinous when crushed.

Bark

Grey-brown and furrowed; young twigs often have corky ridges.

Fruit

Spiky, woody balls 2–4 cm across on a long stalk.

Difference from sycamore

In sycamore the leaves are opposite and coarsely toothed.

Difference from London plane

The London plane has a larger, less star-shaped leaf and flaking bark.

Flowering: April–May · Pruning: November–March

Identify by feature: Palmate leaves · Red autumn colour

Looks like it, but isn’t

• Sycamore Acer pseudoplatanus: leaves are opposite and coarsely toothed. Difference from sycamore
• London plane Platanus × hispanica: larger, less star-shaped leaf and flaking bark. Difference from London plane

Why grow it?

• The finest autumn colours you can have in a garden: yellow, orange, red and purple all at once.
• Glossy, star-shaped leaves that smell resinous when crushed.
• A regular, graceful crown, also handsome as an avenue tree.
• In winter the corky ridges and spiky balls catch the eye.

Sweetgum: where does it grow best?

• Full sun: that is where the autumn colours are best.
• Acid to neutral soil that doesn’t dry out; on chalky soil its leaves turn yellow (chlorosis).
• Allow for a crown 10 m wide and 20–25 m tall; for a smaller garden there is the narrow columnar form ‘Slender Silhouette’.
• Don’t plant it next to a patio or path: the spiky fruits drop all winter.

Light

Full sun

Legal basis

Acid soil

Moisture

Normal

Size

25 m tall, 10 m wide

Hardiness

Throughout Belgium, no protection needed

Goes well with

• Tulip tree: Another North American park tree, with golden-yellow autumn colour next to the reds and purples of the sweetgum.
• Snowy mespilus: A small tree with blossom in April and an equally fiery autumn colour.
• Japanese maple: A small tree for acid soil, with equally beautiful autumn colour.

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

Sweetgum: when and how to plant it?

1. Plant from November to April, root-balled or container-grown, preferably in spring.
2. Choose a young tree: a large tree establishes with difficulty.
3. Dig a generous planting hole and mix in leaf mould; on truly chalky soil you are better off choosing another tree.
4. Put a stake on the windward side and tie the trunk loosely.
5. Water generously after planting and during dry spells in the first few years.

Care

Watering

In dry spells during the first few years; it likes soil that doesn’t dry out.

Feeding

Not needed; leaf mould or mulch keeps the soil slightly acid and moist.

Autumn colour

Shade and too much fertiliser make the autumn colour duller: give it sun and don’t feed it.

Fruits

In winter, rake the fallen balls off the lawn and paths: they break down slowly and are prickly.

Tip: Choose your tree in autumn at the nursery: seedlings colour very differently. Varieties such as ‘Worplesdon’ colour reliably every year.

Sweetgum: when to prune it?

Pruning months: November–March.

When: Dead, diseased and broken branches can be removed at any time of year. If pruning is needed, do it during winter dormancy (November–March).

How:

• Needs little pruning; keep a single leader.
• On a young tree, remove competing leaders and crossing branches.
• Raise the crown of an avenue tree gradually by removing a few of the lowest branches at a time.

Caution: Cut large branches in three steps, just outside the branch collar, and don’t prune in hard frost.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Sowing

Sow the seeds from the balls outdoors in a seed tray in autumn; they germinate after winter. Seedlings vary greatly in their autumn colour.

Grafting

Varieties with reliable autumn colour or a narrow habit are grafted; that is a job for the nursery.

Sweetgum: how does it get through the winter?

Hardy throughout Belgium: no protection needed.

• Hardy in Belgium and the Netherlands.
• The leaves often hang on for a long time and keep colouring into November; after that, the corky ridges and spiky balls catch the eye.

Diseases and pests

• Chlorosis: Yellow leaves with green veins on chalky soil. Add leaf mould or an acid mulch; on truly chalky soil, plant another tree instead.
• Poor autumn colour: Caused by shade, very rich soil or a seedling with dull colouring. Plant in sun and choose a variety such as ‘Worplesdon’.
• Spiky fruits: On lawns and patios they are unpleasant to walk on; rake them up regularly.

Through the year

• January: Formative pruning of young trees in mild weather.
• February: Clear up fallen balls; remove dead branches.
• March: Last month for pruning; plant root-balled or container-grown trees.
• April: Planting; the leaves unfold.
• July: Water young trees in dry spells.
• October: The autumn colour begins: yellow, orange, red and purple.
• November: Autumn colour at its best; winter pruning can begin.
• December: The balls drop; remove dead branches.

What can you use it for?

Garden and landscape

Street and garden tree with the finest autumn colours.

Also used for

The fragrant resin (liquid amber, ‘styrax’) was used in perfume and incense.

Did you know?

• Famous for its spectacular autumn colours: yellow, orange, red and purple on the same tree.
• The fragrant resin (liquid amber, ‘styrax’) was used in perfume and incense; it also gave the tree its name, Liquidambar.
• The star-shaped leaf looks like a maple leaf, but it is alternate; in maples the leaves are always opposite.
• In the wild it grows from the eastern USA to the mountains of Mexico and Central America.
• Its seeds contain shikimic acid, the same substance that is extracted from star anise as a raw material for the flu drug Tamiflu.