Trident maple

Identification and origin

Acer buergerianum belongs to the Sapindaceae family, which now includes the maples. It is native to north-central, south-central and southeastern China and to Taiwan, and it has naturalized in Korea and in a few parts of Europe and Central Asia. The species name honors Heinrich Bürger, a 19th-century German botanist.

It is a small to medium-sized deciduous tree with a rounded to oval crown. In cultivation it usually reaches 26–39.5 ft tall and 13–26 ft wide after ten to twenty years; growth is slow to moderate. It tends to grow with several stems and low branches, but it can be trained to a single trunk.

The opposite leaves measure 2–4 in. They carry three triangular lobes pointing forward, the central lobe being the longest: this trident outline gives the tree its name. Bronze as they unfold, they turn glossy dark green, paler and grayish underneath. In fall they color yellow, orange or red, often later than other maples.

Small greenish-yellow flowers appear in spring in corymbs; they are not showy. In fall they give way to winged samaras about 1 in long, borne in pairs. The bark, smooth and gray on young trees, flakes off with age in plates that reveal orange-brown inner bark, one of its winter attractions.

Several cultivars are available: ‘Mino Yatsubusa’, a dwarf with long, narrow leaves; ‘Kifu Nishiki’, with rounder leaves and slow growth; ‘Naruto Kaede’, whose leaves curl inward; ‘Streetwise’, with a single trunk and red fall color. The variety formosanum, from Taiwan, is also prized for bonsai.

Light

Full sun suits it best, with at least six hours of direct light a day; it also accepts partial shade. Any aspect works, but it appreciates a sheltered position. In sun, its foliage stays more compact and its leaves smaller, which bonsai growers look for. In a container, shield it from harsh afternoon sun during the hottest weeks.

Watering

In the ground, once well established, trident maple tolerates drought and copes with soil that is occasionally dry or occasionally wet. A 3–4 in layer of mulch under the canopy, covering exposed roots, helps keep the soil cool and moist.

In a container things are different: the tree is vigorous and uses a lot of water while growing. Check the mix with a finger and water as soon as the surface starts to dry, without leaving it soggy. If the leaves droop slightly from lack of water, prompt watering usually brings them back. In winter, keep the root ball moist but not wet. Prefer rainwater to very hard water, which eventually yellows the foliage.

Potting mix

It adapts to clay, loam or sandy soils, ideally fertile, moist and well drained. Slightly acidic to neutral soil suits it best: above pH 7, chlorosis can appear. It tolerates soil compaction and some salt. In a container, choose a fast-draining mix with a pH between 5 and 7.

Temperature

Trident maple is hardy in USDA zones 5a to 9b. Planted in the ground, it withstands northern European winters, down to -4–5 °F. It stands up well to wind and air pollution, which makes it a good urban tree.

Grown in a container it is far more vulnerable: its roots hold a lot of water and are sensitive to frost, and a frozen root ball can be fatal. Do not expose it to temperatures below 23 °F; in winter, move it to a frost-free greenhouse or a cold room. Its wood sometimes breaks under the weight of snow or ice.

Repotting

It transplants easily. In a container, repot in early spring, just before the buds open. Young trees, whose roots grow very fast, can need repotting every year; older trees every two or three years. The roots tolerate heavy pruning. Trim off any that died back over winter to make room for new growth.

Pruning

It needs little pruning. Avoid pruning in spring, when the sap is rising: cuts bleed heavily. The recommended period runs from late fall to midwinter; light pruning in late summer or early fall slows growth very little, because the tree keeps its leaves for the whole season.

For a shade or street tree, you can select a single trunk and gradually raise the lower branches so people can walk beneath the canopy. As bonsai it tolerates repeated pruning and even defoliation: a dedicated guide is available on this site.

Propagation

Seed is the most common method. Sow in fall or spring. The seeds keep poorly when dry: store them in the refrigerator, then soak them for a day in hot water before about three months of cold, moist stratification. Softwood cuttings root in early summer and hardwood cuttings in late winter; air layers root easily.

Common problems

Trident maple is seldom troubled by diseases or pests. Like other maples, it can be affected by verticillium wilt, a fungus that wilts and kills whole branches. Aphids are the most frequent pests; scale, caterpillars, spider mites and borers are less common. Powdery mildew, leaf spots, anthracnose and cankers are also possible. Yellowing foliage often points to soil that is too alkaline; rotting roots, to overwatering in a container.

Remember that one symptom can have several causes: wilting, for example, can come from too little water, too much water or verticillium wilt. Look at the whole tree and its growing conditions before acting.

Toxicity

No toxicity is reported for trident maple in dogs or cats. Horse owners should still be careful with maples in general: the wilted leaves of red maple, a related species, are toxic to horses and damage their red blood cells.