American sweetgum

Identification and origin

Liquidambar styraciflua belongs to the Altingiaceae, the sweetgum family, which was long included in the witch hazel family. It is native to the eastern United States, from Connecticut and Pennsylvania south to Florida and Texas, and to Mexico and Central America, from Belize and Guatemala to Nicaragua. It has been introduced in Europe, notably in Belgium, Italy and Spain. In its native range it often grows in river bottomlands.

In cultivation it is a tree 59–75.5 ft tall, sometimes up to 98.5 ft, and 34.5–49 ft wide, with a trunk that can exceed 4 ft in diameter. The crown is pyramidal to oval. It grows fairly fast but takes more than fifty years to reach its mature size.

• Leaves: alternate, simple and star-shaped, with five to seven pointed, toothed lobes, 4–6 in long. Glossy dark green above and paler beneath, they are fragrant when crushed. In fall they turn yellow, orange, red, purple or burgundy and hang on the tree for a long time.
• Flowers: inconspicuous, yellow-green or tinged red, in early spring. Male flowers form upright clusters 3–4 in long; female flowers form drooping round heads about 1 in across.
• Fruit: spiny, woody balls 1–2 in across, made of beaked capsules, brown when ripe. They often stay on the tree all winter; birds eat the seeds.
• Bark: grayish brown and deeply furrowed, with interlacing ridges that turn almost white with age. Some trees, especially in the northern part of the range, have corky projections on the twigs.

Its leaves look like a maple’s, but they are alternate. Several cultivars are available:

• ‘Rotundiloba’: rounded lobes, a narrow habit and, above all, no fruit.
• ‘Moraine’: reputed to be the most cold hardy.
• ‘Burgundy’: burgundy-red fall color, late-holding leaves, less cold hardy.
• ‘Festival’: narrow, upright habit, peach-colored fall foliage, less cold hardy.
• ‘Palo Alto’: a symmetrical pyramidal habit, bright orange fall color.

Light

Full sun suits it best; it accepts partial shade. It tolerates both exposed and sheltered sites, and any aspect except north-facing. Give it a large, open space: its roots and crown take up a lot of room.

Watering

Its drought tolerance is moderate at best. An established tree appreciates soil that stays moist: during a long dry spell, check moisture deep down and water thoroughly if the soil has dried, without a fixed schedule. On the other hand, it handles wet soil and even short-term flooding well, a legacy of the bottomlands where it grows wild. Drought and construction damage sometimes cause dieback at the top of the crown.

Potting mix

It adapts to clay, loam or sand that is moist but well drained, ideally deep: it grows poorly in shallow, droughty soil. The pH should be acidic to neutral, no higher than 7. Iron chlorosis often appears in alkaline soil.

Temperature

It is hardy in USDA zones 5a to 9b, which means winter lows of about -20 °F, and it does not mind intense heat. Some cultivars, such as ‘Burgundy’ and ‘Festival’, are slightly less cold hardy; ‘Moraine’ is the hardiest. Grown in a container or as a bonsai, however, it needs protection from hard frost, because its roots are far more exposed than in the ground.

Repotting

In the ground, sweetgum is difficult to transplant. Ideally, plant a young container-grown tree in spring: its roots take three to four months to recover from transplant shock. Its large surface roots can lift curbs and sidewalks: plant it at least 8–10 ft from curbs and paths.

In a container or as a bonsai, repot every two or three years in early spring, while it is still dormant, in a free-draining neutral to slightly acidic mix. The roots grow vigorously and tolerate normal to heavy root pruning.

Pruning

In the ground it needs only minimal maintenance pruning. A tree lightly affected by canker can be cleaned up by pruning. Prune in spring, after bud break. Avoid pruning during winter dormancy: it encourages twig dieback, and the wounds heal poorly. Remove caterpillar nests while they are still small by cutting off the branch tip; never burn them in the tree.

Propagation

• Seed: the most common method. Seeds germinate so readily that volunteer seedlings sometimes form thickets in nearby beds.
• Cuttings: semi-hardwood cuttings or root cuttings.
• Root suckers and air layering: two other ways to get a young plant.

Common problems

A single symptom can have several causes: yellowing can come from overly alkaline soil, drought or roots damaged by construction work. Look closely at the tree before treating it. In a good spot it usually stays healthy.

• Chlorosis: in alkaline soil, the foliage turns yellow.
• Caterpillars: bagworms, which web leaf pieces into sacks, plus tent caterpillars and fall webworms, which spin webs over branches and feed inside them.
• Scale insects: several species, including walnut scale and cottony cushion scale, settle on the branches; horticultural oil in spring keeps them in check.
• Leaf miner: brown blotches on the leaves.
• Canker and bleeding necrosis: sunken areas on the trunk, sometimes with heavy bleeding. There is no chemical control; a severely infected tree can die.
• Leaf spots: they can cause early leaf drop but are rarely serious; rake up and dispose of infected leaves.
• Root rot: the tree can be susceptible to honey fungus (Armillaria). It is resistant to verticillium wilt, however.
• Fruit: falling fruit litters the ground and makes hard surfaces slippery; choose ‘Rotundiloba’ near a patio.

Toxicity

No toxicity has been reported: American sweetgum does not appear among the plants listed as toxic to dogs and cats. Even so, keep children and pets from chewing on any part of the tree.