The Japanese emperor oak is a deciduous tree with very large leaves. It is frequently found in gardens and pruned to keep its appeal. In Japan, the people use the leaves to wrap a sweet treat called Kashiwa mochi during the celebration of Children’s Day.
I. Appearance and Characteristics
Quercus dentata, also called Japanese emperor oak or daimyo oak (Japanese: 柏, kashiwa; traditional Chinese: 柞櫟; simplified Chinese: 柞栎; pinyin: zuòlì; Korean: 떡갈나무, tteokgalnamu) is a species of oak native to East Asia (Japan, Korea and China). The name of the tree is often translated as “sweet oak” in English to distinguish it from Western varieties. It is placed in section Quercus.
Quercus dentata is a deciduous tree growing up to 20–25 metres (66–82 feet) tall, with a trunk up to 1 m (3 ft 3 in) in diameter. Its foliage is remarkable for its size, among the largest of all oaks, consisting of a short hairy petiole, 1–1.5 centimetres (3⁄8–5⁄8 inch) long, and a blade 10–40 cm (4–15+1⁄2 in) long and 15–30 cm (6–12 in) broad, with a shallowly lobed margin; the form is reminiscent of an enormous pedunculate oak leaf. The leaves are often retained dead on the tree into winter. Both sides of the leaf are initially downy with the upper surface becoming smooth.
The flowers are produced in May; the male flowers are pendulous catkins. The female flowers are sessile, growing near the tips of new shoots, producing acorns 1.2–2.3 cm long and 1.2–1.5 cm broad, in broad, bushy-scaled cups; the acorns mature in September to October.
Quercus dentata was introduced to the British Isles in 1830, where it is occasionally grown in botanical gardens. It is usually smaller in cultivation than in the wild, growing to a small angular tree or large irregular shrub.
II. How to Grow and Care
Sunlight
Japanese emperor oak thrives in full sun conditions, where it receives direct light for at least 6 hours a day to fuel its growth and maintain robust health. However, Japanese emperor oak is also adaptable and can withstand partial sun, which allows for some daily respite from intense light. In non-optimal light, such as extended periods of partial sun, Japanese emperor oak’s growth rate may be compromised, and its foliage may not be as lush.
Adaptive traits such as leaf size and orientation can help Japanese emperor oak maximize light capture. When grown outdoors, Japanese emperor oak should be planted in locations with clear exposure to the sky, avoiding deep shade from larger structures or trees.
Temperature
Japanese emperor oak grows in a large range of temperatures. It is adaptable in hardiness zones 5-9.It prefers well drained soil with adequate ventilation in the tree canopy. Japanese emperor oak will not do well in standing water. Also, leaf molds pose serious threats if the leaves cannot dry out in the wind. So make sure they are not stuck against buildings where rainwater may drain.
Watering
Japanese emperor oak thrives in environments that mimic its native woodland habitat, where it has adapted to withstand periods of low moisture. This species exhibits a preference for moderate humidity and is relatively drought-tolerant once established. For optimal health, Japanese emperor oak should be watered once every two weeks, allowing the soil to dry out slightly between watering sessions. Typically grown outdoors due to its size and growth pattern, Japanese emperor oak benefits from mulching which helps retain soil moisture and mimics the leaf litter of its natural setting.
Soil
Ideal soils are well-drained loam, sandy-loam, or sandy-clay soils. Some alluvial fan areas and silts harbor good oaks stands. The key in all of these is that the soil is well-drained. Standing water cannot be tolerated by oaks.
Fertilizing
To encourage vigorous growth and fortify health, japanese emperor oak thrives with balanced nutrition fertilizers in spring and high nitrogen varieties come fall. Apply fertilizer in moderation, matching japanese emperor oak’s active growth cycles; monthly during spring through summer and bi-monthly in autumn. Minor applications prevent over-concentration, safeguarding root systems. Adjust feeding with seasonal shifts to optimize nutrient uptake and support lifecycle stages. Diligently incorporate fertilizers into soil to foster even distribution and prevent root burn, ensuring a robust japanese emperor oak.
Planting Instructions
It may take a very long time if you want to get a mature oak tree from an acorn. But with patience, planting a small tree is still fun. Be sure to kill weevil larvae by soaking the acorns in 41 ℃ water for 30 minutes, stratify in moist sand in the refrigerator (not freezer), and plant in the springtime.
Pruning
Branches should be pruned to avoid moist pockets or where heavy branches may fall on people or buildings. Avoid having branches that grow with leaves tight together or pressed against buildings. If rain collects in these pockets then molds and fungi can attack. Japanese emperor oak love having their leaves dry out in a well ventilated breeze.
To ensure that no danger occurs from the brittle hardwood branches, make sure that heavy branches do not hang over walking paths or outbuildings. Also, do not let children play near oaks in a thunderstorm as they are susceptible to falling branches and lightning strikes.
Propagation
Japanese emperor oak is multiplied effectively through sowing. For successful germination, stratify the acorns to simulate winter conditions, which helps break seed dormancy. Upon sprouting, transplant seedlings to individual pots filled with well-draining soil, ensuring ample space for root development. Regular watering and partial sunlight encourage healthy growth. As Japanese emperor oak is intolerant to disturbance, minimize root handling during transplantation to its permanent location.
Transplanting
The optimal period to transplant Japanese emperor oak is during autumn to early winter (S3-S4), when the plant is dormant. This timing reduces shock and promotes root development. Japanese emperor oak prefers areas with full sun to part shade. When transplanting, ensure the hole is twice the root ball’s width.
III. Uses and Benefits
In Korean cuisine, its acorns (in Hangul: 도토리, dotori) have been used since the Three Kingdoms. A notable food is dotorimuk.
In Japanese cuisine, its leaves are used as a wrapping for kashiwa mochi.
