Siebold’s maple is a striking tree native to Japan and Korea. It is valued for its vibrant fall colors, which range from gold to deep red. Unlike other maples, its bark often peels away in thin, curled strips, adding texture to its trunk and branches.
I. Appearance and Characteristics
Acer sieboldianum (Siebold’s maple; Japanese: コハウチワカエデ, romanized: kohauchiwakaede) is a species of maple native to Japan and common in the forests of Hokkaidō, Honshū, Shikoku and Kyūshū Islands; in the south of the range it is restricted to mountain forests. It is named after Philipp Franz von Siebold.
It is a slow-growing, small to medium-sized deciduous tree growing to 10–15 meters (33–49 ft) tall, with smooth gray-brown bark. The young shoots are green to red, thinly covered with white hairs in their first year.
The leaves are mid to dark green, 4–8 centimeters (1.6–3.1 in) long and 5–10 centimeters (2.0–3.9 in) broad with a 3–7 centimeters (1.2–2.8 in) petiole, and palmately lobed with nine to eleven (occasionally just seven) lobes. The young leaves in spring are downy with white hairs, with the petiole and veins on the underside of the leaf remaining hairy all summer, a feature useful in distinguishing it from the related Acer palmatum. In autumn, the leaves turn bright orange to red.
The flowers are pale yellow, produced in combs of 10–15 together; it is andromonoecious, with inflorescences containing flowers with either both sexes, or just male. The fruit is a paired samara, the pair spreading horizontally, each seed with a 15–20 millimeters (0.59–0.79 in) wing. Flowering is in late spring, with fruit maturation in early autumn.
The smooth bark and yellow flowers help distinguish it from the closely related Acer japonicum (Japanese, hauchiwakaede), which has rough, scaly bark, and red flowers, while the hairy stems and yellow flowers distinguish it from Acer shirasawanum (Japanese, ooitayameigetsu; with hairless stems and red flowers).
Siebold’s maple is not as rare in cultivation as it seems. Specimens are often mistaken for and mislabeled as similar species in the series Palmata, such as Acer japonicum, Acer shirasawanum and Acer palmatum; it is also sometimes confused with Acer pseudosieboldianum (Korean Maple or Keijo Maple), a closely related species from the adjacent mainland of northeastern Asia.
Several cultivars have been selected, most only rarely seen outside Japan. Cultivars include ‘Kinugasa yama’, ‘Mi yama nishiki’, ‘Ogura yama’, ‘Sode no uchi’ and ‘Osiris’.
II. How to Grow and Care
Sunlight
The siebold’s maple has a certain requirement for sunlight and prefers a partially shaded area. In cases of exposure to direct sunlight in the summer, the leaves of most varieties will wither, so shading is required. As the plants get older and their root system grows, this condition will be less of a problem. A few varieties will tolerate exposure to direct sunlight, such as ‘Beni Maiko’ and ‘De Shojo’. Some weeping varieties can also tolerate exposure to direct sunlight, such as ‘Ao Shidare’.
Sunlight conditions will directly affect the ornamental appearance of siebold’s maple leaves. In the spring, sufficient sunlight will make the maple leaves more vivid, while in cases of insufficient sunlight or partial shading the leaf color may fade. During the fall, sunlight can also affect the leaf color. For potted plants, full exposure to sunlight is recommended during the spring and the fall, with partial shading in the summer.
Temperature
The siebold’s maple has good cold resistance and is able to tolerate low temperatures. The siebold’s maple is native to the margins of forests in China, Japan, and North Korea, so these trees generally prefer a humid environment. Most siebold’s maple plants have shallow root systems, so they should be watered frequently during the summer. For some varieties, a sprayed mist should be provided during the summer to increase the humidity of the air around them.
Watering
Originating from the cooler climates of East Asia, siebold’s maple is well-adapted to environments with moderate moisture. This species thrives on a balance between hydration and drainage, showing a preference for consistent soil moisture without being waterlogged. Accordingly, it should be watered once every 1-2 weeks, ensuring the soil dries slightly between watering sessions. As a deciduous plant, siebold’s maple’s water needs decrease during its dormancy in the colder months; therefore, indoor cultivation typically requires less frequent watering compared to outdoor growth.
Soil
The siebold’s maple does not have many specific requirements for soil. It is a forest native, so it prefers well-drained soil that is rich in humus and slightly acidic. Its main root will extend deep into the soil, but its tiny fibrous roots will be concentrated near the soil surface, so accumulated water in the soil tends to cause root rot.
Fertilizing
Potted seedlings should be given slow-release fertilizer only. For seedlings grown in gardens, fertilizer should be applied three times a year: once in the early spring, once in early summer for the growth period, and once in the fall.
Planting Instructions
The best time for planting or transplanting a siebold’s maple is following defoliation in the fall. At this time, the leaves will have fallen off so there is little transpiration and water loss can be avoided. In addition, the root system will still be growing at this time, preparing for regrowth the following spring. Transplanting should be avoided on the coldest days because cold wind can kill some of the shoots and branches. During the winter, in areas that cannot be sheltered from the wind, it is recommended to cover the branches.
Pruning
Pruning is mainly used to enhance internal ventilation, improve shoot formation, promote growth, and for shaping. The common approach to pruning is to remove any old or weak branches, remove any branches that disrupt the shape of the tree, and remove any branches that cross other branches. Pruning is used to control the plant according to the required height and shape. Generally, this follows the “Y-type” pruning method.
It is possible to prune a siebold’s maple throughout the year, but the coldest winter months should be avoided to prevent damage to the plant. Major pruning to shape a maple can be performed following defoliation in the fall, or prior to leaf growth in the spring. It is recommended to prune in the fall because withered and full buds can be easily distinguished.
According to the shaping plan, you can prune any withered buds and keep the full ones, thus making your tree healthier. For pruning in the summer, diseased, weak, or dead branches can be removed, mainly to enhance the tree’s ventilation.
If grown as a potted plant, the roots can easily occupy the entire flowerpot due to the limited space. This can make a siebold’s maple prone to aging if an old flowerpot is not changed. It is recommended that old roots are pruned during the dormancy period, that is, cut off any old, coarse, diseased, and weak roots.
Propagation
Common propagation methods include grafting, taking cuttings, and sowing seeds.
Grafting is the most common propagation method. Seedlings of Acer palmatum or Acer oliverianum are usually selected for the rootstock. Grafted seedlings have strong roots and grow rapidly, but poor affinity is occasionally present in some cases. Seedlings with Acer oliverianum as the rootstock are less hardy.
Cuttings take longer to grow and are mostly used in the production of bonsai.
Sowing seeds is a common way to cultivate new varieties. The hybrid offspring of two different maples are sown and valuable individuals are then selected from the seedlings. The traits of the parents may not be maintained in the selected offspring.
III. Uses and Benefits
Its small size and upright habit make Acer sieboldianum an excellent choice for the small garden.