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

Description and Botany

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

Liquidambar styraciflua, also called “American sweetgum”, is best-known species. It is available in many cultivars selected for habit, more modest dimensions, shape and colour of foliage 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 liquidambar” 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 genus.

In natural habitat, American sweetgum can reach up to 40 m in height, but locally it seldom exceeds 20 m on average with 3 to 5 m spread. It shows slow growth during first years, then fairly rapid growth afterwards. It forms a stately specimen fairly quickly. New varieties offer more modest dimensions, rarely exceeding 10 m in height and 3–4 m wide after 10 years. It has very good longevity of about 150 years.

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

Liquidambar styraciflua – botanical illustration by P.J. Redouté

On a strong taproot, this handsome tree develops a very vertical trunk with corky bark of dark grey turning brown-red and fissuring with age. Young shoots show wrinkles that become corky outgrowths as they age. Wood is valuable and so similar to walnut that Liquidambar was commonly nicknamed “satin walnut”. Its bark emits a cinnamon scent and exudes a resin, styrax or copal, sometimes called “White Peruvian balm”, which gave tree its name liquidambar meaning “liquid” and “amber”, referring to balsamic, aromatic sap of amber colour that flows when bark is cut.

Liquidambar is especially prized for elegant deciduous foliage that takes on sumptuous hues, filling garden with warm, spicy colours as days shorten in autumn. Foliage consists of large palmate leaves, divided into 3 to 7 triangular or rounded lobes (Liquidambar styraciflua ‘Rotundiloba’), more or less notched and reminiscent of maple leaves except that sweetgum leaves are arranged alternately on shoots and not opposite. Broad 10 to 18 cm, with finely dentate margin, they are pubescent, bristly with reddish hairs on underside of lamina.

This ample palmate foliage releases a turpentine scent when crushed.

As with many trees of family Hamamelidaceae, liquidambar wears magnificently coloured foliage in autumn. From pale green to glossy dark green, sometimes bright green speckled and splashed with yellow or grey margined with cream from spring to summer, leaves turn flamboyant shades of gold, orange, ochre-yellow, copper, crimson red to garnet and pinkish-purple in autumn, intensity varying with cultivar and growing conditions.

Flowering of sweetgum is discreet. In spring, in April, small green-yellow apetalous unisexual flowers appear. Sweetgum is a monoecious species: male and female flowers coexist on same tree. They take 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, female flowers bristly with green points turn into fruits, brown spherical capsules 2.5 to 3.4 cm which release small winged seeds reminiscent of maple samaras. They persist through winter attached to shoots by a long peduncle.

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

With excellent hardiness, liquidambar tolerates winter cold down to -15–20 °C, sometimes even lower. It thrives in sun and reveals best colours on non-calcareous (slightly acidic), deep, heavy (clayey), rich and fresh soil. It is an accommodating tree that tolerates temporarily waterlogged soils, even sea spray and pollution.

Plant in isolation on a short grass meadow in a large park or spacious garden, near a pond, in alignment along a long avenue or on property boundary in a coastal garden.

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

Finally, fragrant and precious wood of liquidambar was much prized in cabinetmaking.

Main species and varieties

Numerous cultivars of Liquidambar styraciflua, the species most widely grown in gardens, are now available, selected for their habit, foliage colour and their more compact growth than that of the typical species. For example, the impressive size of this tree has been happily reinterpreted in the more compact form of the ‘Gum Ball’ cultivar, finally allowing liquidambar to feature in smaller gardens.

Most popular

Liquidambar styraciflua Gum Ball - American Sweetgum

This American sweetgum is notable for its extremely compact growth and attractive rounded 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 prized for its magnificent autumn colours ranging from orange to scarlet and purplish hues. Plant in a well-exposed, open spot in the garden, as a solitary specimen 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

This cultivar has much less vigorous growth than the typical species, making it particularly suited to small gardens. It also stands out for its remarkable variegated foliage, turning yellow-orange 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 makes a statement in 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 with a more conical habit than the typical species and very decorative fragrant foliage in yellow-orange in autumn. To grow both as a solitary specimen and 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° to -20°C, allowing planting in all regions. However, in regions with long winters, give it a well-sheltered spot because late frosts could damage its aments. Native to wet areas and 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 sumptuous autumn colours. It prefers heavy, cool soils. It needs a clay or clay-loam soil, rich, deep, draining in winter, cool, even moist, as it requires a certain moisture in the soil to thrive. Its root can tolerate temporary immersion but dislikes marshy ground!

It prefers rather acidic soil, in any case not calcareous. Although it dislikes calcareous soils, this tree is tolerant of urban pollution and will be a good candidate for city gardens.

Because its taproot handles transplanting poorly, think carefully about the location before planting as once well rooted it will grow about 40 to 50 cm per year. Give it space to match its size because at ripeness the largest sweetgums reach 20–22 m in height on average with 7 m spread.

To make the most of its remarkable autumn display and elegant silhouette, reserve for this tree a well-exposed, open position in garden.

Its impressive 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 a tree for lining to border an avenue majestically or to grace a pond in which it can be reflected.

In a garden where space is limited, to thicken a copse of bushes, or an informal hedge, choose a dwarf American sweetgum variety, such as Liquidambar styraciflua ‘Gum Ball’ which will not exceed 3 m in any direction.

When to plant?

Plant the liquidambar or copalme preferably in autumn, from September to November to encourage rooting before winter. Container-grown specimens can also be planted in spring from February to April, avoiding frost periods or extreme heat.

How to plant?

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

For planting 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 potting compost into garden soil, adding heather soil if ground is calcareous
• Add well-rotted compost
• Plant tree at collar level
• Stake if necessary
• Firm soil and water regularly until establishment and during first years
• Mulch to keep base cool during hot periods

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

Care and pruning of Liquidambar

Liquidambar requires very little maintenance and grows without any special care.

During its first years, it requires regular watering. In summer, monitor its water needs and water generously in dry weather. Once well established, it will be content with rain!

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

Each spring, amend soil with a good organic fertiliser such as farmyard 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, lightly prune misplaced or overcrowded branches.

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

Multiplication

Sweetgum can be propagated by sowing (a very long process; germination can take up to 2 years), by division of suckers, by propagation by cuttings (rather unreliable) 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 suckers with a spade, cutting the root as close as possible to the main trunk. Replant these young plants immediately in fresh soil.

By layering

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

• In autumn, bend a low branch down to the base of the tree
• Remove leaves from that section of stem and make a small incision in the bark for a few centimetres
• Dig a furrow close to the parent plant
• Lay the branch in the furrow and bury part of it so it can root
• Backfill the furrow and secure the layer with metal hooks
• Raise the tip and stake the aerial part
• You can separate the layer from the parent plant and replant in open ground when it has developed sufficient roots

Taking Liquidambar cuttings

• In autumn–winter, using a pruning shear, take hardwood cuttings about 20 cm long
• Remove leaves from the base of the stem
• Plant cuttings into buckets, in a mix of sand, turf and moist soil
• Keep substrate moist until rooting
• Establishment is slow and may take several years
• Once well rooted, repot individually into pots filled with compost and replant following autumn

Companion planting for American sweetgum

The American sweetgum needs plenty of space; it is a tree that stands on its own and will be remarkable as a majestic punctuation in the middle of a short grass meadow in a large garden. It is nevertheless easy to combine with other plants that enjoy similar cool conditions and deep soil. Resistant to both pollution and sea spray, its presence is essential in large city garden as well as in seaside gardens where it can line a path. With its colourful foliage, it is indispensable for creating stunning autumnal atmospheres.

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

An example of an autumnal planting in a grove: Liquidambar styraciflua, Liriodendron tulipifera, Nyssa sylvatica and Parrotia persica

You will create a dazzling grove in autumn by pairing it with a Tulip tree (Liriodendron tulipifera), Oxydendrum arboreum, Parrotia persica and black tupelo, which also dress in sumptuous autumn colours.

This tree, which prefers acidic soils, can serve as backdrop to a mix of heather soil bushes such as dwarf Rhododendrons, hydrangeas, Chinese azaleas.

To fully enjoy its splendour, plant it against permanent green backdrop composed 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’ on which you could 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, Dutch irises, Anemone nemorosa, botanical tulips and train a Clematis montana up it to complete that springtime enchantment.

Carpet its base with some evergreen ground-cover perennials such as creeping bugles or heucheras with sumptuous evergreen leaves in brick red or deep purple, dead-nettle, a variegated ivy, hardy geraniums or a sweet violet that 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.