<em>Liquidambar</em>, American sweetgum: planting, pruning, care

Description and botany

The Liquidambar is a deciduous tree of the Hamamelidaceae family, like Hamamelis and Parrotia. The genus comprises four tree species native to temperate forests and the banks of large rivers in America, Turkey and Asia.

The Liquidambar styraciflua, also called “American sweetgum”, is the best-known species. It occurs in numerous cultivars selected for habit, more modest dimensions, leaf shape and colour, such as ‘Gum Ball’, a dwarf variety not exceeding 3 m, ‘Golden Sun’ with pale yellow foliage in spring then green in summer, or ‘Aurea’ with green foliage speckled with yellow.

Liquidambar orientalis, “Oriental sweetgum” or “Styrax of the Levant”, native to Turkey, Liquidambar acalycina or “Chinese liquidambar”, both smaller than their American cousin, and Liquidambar formosana from Taiwan, with foliage equally magnificently coloured in autumn, complete the genus.

In its natural habitat, the sweetgum can reach up to 40 m in height, but in our regions it will seldom exceed 20 m in height on average with a 3 to 5 m spread. It grows slowly in the first years then fairly quickly thereafter. It relatively quickly forms an impressive specimen. New varieties offer more modest dimensions, rarely exceeding 10 m in height for 3–4 m in width after 10 years. It displays a very long lifespan of about 150 years.

Slender or columnar, conical or pyramidal, more rarely ball-shaped (‘Gum Ball’) or rounded, the habit of Liquidambar varies considerably according to species and cultivars. It most often, however, takes a pyramidal silhouette, sometimes quite irregular, which rounds with age.

Liquidambar styraciflua – botanical illustration by P.J. Redouté

On a powerful taproot, this handsome tree develops a very upright bole with corky bark of dark grey turning brown-red and splitting with age. Young shoots show ridges that become corky outgrowths as they age. Its wood is valuable and so similar to walnut that Liquidambar was commonly nicknamed “satin walnut”. Its bark exhales a cinnamon scent and releases a resin, styrax or copal, sometimes also called “white balm of Peru”, which earned the tree its name liquidambar meaning “liquid” and “amber”, referring to this balsamic, aromatic sap of amber colour that flows when the bark is incised.

Liquidambar is particularly valued for its elegant deciduous foliage which adopts sumptuous hues, filling the garden with warm, spicy tones as days shorten in autumn. The foliage is composed of large palmate leaves, divided into 3 to 7 triangular or rounded lobes (Liquidambar styraciflua ‘Rotundiloba’), more or less notched resembling maple leaves except that sweetgum leaves are arranged alternately on the shoots and not opposite. 10 to 18 cm wide, with a finely dentate margin, they are pubescent, bristly with rusty hairs on the underside of the lamina.

This ample palmate foliage gives off a turpentine scent when crushed.

As with many trees of the Hamamelidaceae family, Liquidambar displays magnificently coloured foliage in autumn. From pale green to dark glossy green, sometimes bright green speckled and splashed with yellow or grey marginate with cream from spring to summer, the leaves take flamboyant shades in autumn: gold, orange, ochre yellow, coppery, crimson to garnet and pinkish-purple, more or less pronounced according to cultivar and growing conditions.

The sweetgum’s flowering is inconspicuous. In spring, in April, small green-yellow apetalous unisexual flowers appear. Sweetgum is a monoecious species: male and female flowers coexist on the same plant. They take the form of erect aments in spikes 5 to 7.5 cm long or of spiky, pendulous glomerules 1 to 3 cm in diameter depending on whether they are male or female.

Only after 25 years of cultivation do the female flowers, bristling with green points, become fruits, brown spherical capsules 2.5 to 3.4 cm in diameter that release small winged seeds reminiscent of maple samaras. They persist for a long time through winter, attached to the branches by a long peduncle.

Liquidambar styraciflua: foliage green then flamboyant in autumn and its fruit

With excellent hardiness, Liquidambar tolerates winter rigours down to -15 to -20 °C, sometimes beyond. It thrives in full sun and reveals its best colours on non-calcareous (slightly acidic), deep, heavy (clayey), rich and moist soil. It is a accommodating tree that will tolerate temporarily waterlogged soils, even accepting sea spray and pollution.

It can be planted as a specimen on a large short grass meadow in a large park or in a sizeable garden, near a pond, in a row along a long avenue or as a boundary tree in a coastal garden.

The resin, styrax or copal exuded by Liquidambar can be burned as incense and is much prized for dermatological and anti-stress properties and for its ability to combat respiratory ailments. Egyptians used it to embalm mummies, while Native Americans chewed it as a form of chewing gum! In the 19th century, when Liquidambar was introduced to Europe, copal resin was used in the preparation of beauty milks and balms. This fragrant gum also serves as a perfume fixative and is widely used by perfumers.

Finally, the fragrant and valuable wood of Liquidambar was highly prized in cabinet-making.

Main species and varieties

Numerous cultivars of Liquidambar styraciflua, the species most widely cultivated in gardens have been selected for their habit, the colour of their foliage and their reduced growth compared with the typical species. For example, the tree’s impressive size has been happily reinterpreted in the more compact cultivar ‘Gum Ball’, finally allowing liquidambar to be grown in smaller gardens.

Most popular

Liquidambar styraciflua Gum Ball - American Sweetgum

This American sweetgum stands out for its extremely reduced growth and attractive ball-shaped habit. A variety to choose for small gardens!

• Flowering time May
• Height at maturity 3 m

See the product sheet

Liquidambar styraciflua - American Sweetgum

This is the typical species, appreciated for its magnificent autumn colours ranging from orange to scarlet red and purple. Plant in a well-exposed position in the garden, solitary or in a row, to admire it in all its splendour.

• Flowering time May
• Height at maturity 20 m

See the product sheet

Our favourites

Liquidambar styraciflua Aurea - American Sweetgum

This cultivar shows significantly less growth than the typical species, making it particularly suited to small gardens. It also features remarkable variegated foliage, turning orange-yellow to scarlet or pink in autumn.

• Flowering time May
• Height at maturity 9 m

See the product sheet

Liquidambar styraciflua Rotundiloba - American Sweetgum

This variety differs from the typical species in the shape of its leaves, cut into rounded lobes. With its slender conical habit, it is perfect for large gardens as a solitary specimen or to line an avenue.

• Flowering time May
• Height at maturity 18 m

See the product sheet

Liquidambar styraciflua Worplesdon - American Sweetgum

This magnificent cultivar stands out for a more conical habit than the typical species and a fragrant, highly decorative yellow-orange foliage in autumn. To grow either as a solitary specimen or in a row.

• Flowering time May
• Height at maturity 12 m

See the product sheet

Planting Liquidambar

Where to plant?

Liquidambar has good hardiness down to -15°–-20°C, allowing planting in all regions. However, in areas with long winters, give it a well sheltered spot as late frosts could damage its aments. Native to wet areas and highly tolerant of sea spray, it will appreciate rainy coastal climates.

It needs maximum light to develop beautiful autumn colours.

It establishes easily in full sun, which will enhance its splendid autumn colours. It likes heavy, cool soil. It requires clay or clay‑loam soil, rich, deep, winter‑draining, cool or even moist, because it needs some soil moisture to thrive. Its root can tolerate temporary immersion while nevertheless disliking waterlogged, marshy ground.

It prefers rather acidic soil, certainly not calcareous. Although sensitive to lime, this tree is tolerant of urban pollution and makes a good candidate for city gardens.

As its taproot copes poorly with transplanting, choose planting site carefully before planting, because once well rooted it will grow about 40–50 cm per year. Give it room to grow as at maturity the largest sweetgums reach 20–22 m in height on average with a 7 m spread.

To best enjoy its remarkable autumn display and elegant silhouette, reserve a clear, open spot in garden for this tree.

Its generous dimensions make it a magnificent specimen to plant as a solitary tree on a large short grass meadow in a vast park or large garden, as an avenue tree to line an avenue majestically or to grace a pond where it can be reflected.

In gardens where space is limited, to bulk up a thicket of bushes or a free‑form hedge, prefer a dwarf American sweetgum variety, such as Liquidambar styraciflua ‘Gum Ball’ which will not exceed 3 m in any direction.

When to plant?

Plant liquidambar or sweetgum preferably in autumn, from September to November, to encourage rooting before winter. Container‑grown specimens may also be planted in spring, from February to April, avoiding periods of frost or extreme heat.

How to plant?

In very calcareous soil, we recommend adding heather soil at planting. Once established, do not move Liquidambar as its root will tolerate transplanting very poorly. Allow enough space — at least 5 to 8 m distance from another tree, 3 to 5 m for cultivars with more limited development. You can also plant in groups of 3 or 5 to create a truly majestic grove.

To plant your sweetgum :

• Start by digging a wide hole at least three times the volume of the rootball
• Spread gravel at the bottom of the hole to improve drainage
• Mix half garden soil with potting compost and heather soil if ground is calcareous
• Add well‑rotted compost
• Plant tree at collar level
• Stake if necessary
• Firm soil and water regularly until established and during first years
• Mulch to retain coolness around the base during hot periods

For successful planting, watch our video on how to plant a tree.

Care and pruning of Liquidambar

Liquidambar requires very little maintenance and grows without special care.

During the first years, it requires regular watering. In summer, monitor its water needs and water generously during dry spells. Once established, it will be content with rainwater!

A good mulch in summer will help keep the soil consistently cool and in winter protect young trees from severe frosts.

Each spring, amend soil with a good organic fertiliser such as manure or compost.

Pruning is neither necessary nor recommended. In autumn or late winter, you may intervene only to remove dead, dry or damaged wood. Between mid‑August and the end of September, prune lightly any poorly placed or surplus branches.

When planted in good conditions, Liquidambar proves resistant to disease.

Multiplication

The Sweetgum can be multiplied by sowing (a very long process, germination can take up to 2 years), by division of suckers, by propagation by cuttings (quite unpredictable) and by layering.

By separating suckers

This is probably the simplest propagation method. Some Sweetgums tend to produce suckers around the parent plant. In autumn, separate the suckers with a spade, cutting the root as close to the main trunk as possible. Replant these young plants immediately into fresh soil.

By layering

Layering Liquidambar is simple and produces a new plant identical to the parent, however root development is very slow.

• In autumn, bend down one of the lower branches to the base of the tree
• Remove the leaves on this part of the stem and make an incision in the bark for a few centimetres
• Dig a furrow near the parent plant
• Lay the branch in the furrow and bury part of it so it can root
• Refill the furrow and secure the layer with metal hooks
• Raise the tip and stake the above-ground portion
• You can separate the layer from the parent plant and replant it in open ground when it has produced sufficient roots

Taking cuttings of Liquidambar

• In autumn and winter, using pruning shear, take hardwood cuttings about 20 cm long
• Remove the leaves from the lower part of the stem
• Plant the cuttings in buckets, in a mixture of sand, turf and moist soil
• Keep the substrate moist until rooting
• Establishment is slow and can take several years
• Once well rooted, pot each individually into pots filled with compost and plant out the following autumn

Companion planting for American sweetgum

The American sweetgum needs plenty of space, it is an essential oil that stands on its own and will be remarkable as a majestic pit in the middle of a short grass meadow in a large garden. It remains easy to pair, however, with other plants that enjoy the same cool conditions and deep soil. Resistant both to pollution and sea spray, its presence is natural in a large city garden as in seaside gardens where it can line an avenue. With its coloured foliage, it is essential for creating magnificent autumn atmospheres.

To compose a symphony of spicy tones, plant it near other trees and bushes with coloured foliage such as Ginkgo Biloba, Acer or Japanese maples, Cornus, birches and Hamamelis.

An example of an autumn grouping: Liquidambar styraciflua, Liriodendron tulipifera, Nyssa sylvatica and Parrotia persica

You will create a dazzling autumn copse by combining it with a Tulip tree (Liriodendron tulipifera), Oxydendron arboreum, Parrotia persica and black gum, which also take on sumptuous autumn tones.

This tree, preferring acidic soil, can serve as a backdrop for a mix of heather soil bushes such as dwarf Rhododendrons, hydrangeas and Chinese azaleas.

To fully enjoy its splendour, plant it against a permanent green background of conifers such as Pinus peuce or Macedonian pine, Taxodium distichum or bald cypress or Metasequoia glyptostroboides ‘Gold Rush’.

An idea for an association: Liquidambar styraciflua (or the superb variety ‘Worplesdon’), Robinia pseudoacacia ‘Frisia’ in which you can train a climbing rose such as ‘American Pillar’ or ‘Maria Lisa’, Cedrus libani ‘Atlantica ‘Glauca’, Festuca ‘Intense Blue’, Sedum ‘José Aubergine’ and Origanum vulgare ‘Aureum’

In spring and summer, accompany its bright green foliage with spring bulbs in acid-green/white tones such as daffodils, , wood anemones, botanical tulips and train a Clematis montana up it to complete the spring enchantment.

Cover its base with some evergreen ground-cover perennials such as creeping bugles or heucheras with sumptuous evergreen brick-red or purple leaves, dead-nettle, a variegated ivy, hardy geraniums or sweet violet which will keep its roots cool.

Smaller sweetgums will easily coexist with a purple hazel, a dwarf Japanese maple, a Ginkgo Biloba ‘Blagon’, a Toona sinensis ‘Flamingo’ or Chinese mahogany.