Silver Birch: Planted by Japan’s Crown Princess Michiko in the Year Our Garden Was Created

BY CORINNE KENNEDY

Japan’s Crown Prince Akihito and Crown Princess Michiko visiting the Seattle Japanese Garden on October 5, 1960. (photo: Densho Digital Registry. from The Ai Chih and Ryo (Morikawa) Tsai Collection) 

This month’s article features a venerable birch tree that was planted four months after the Seattle Japanese Garden’s 1960 opening. Japan’s Crown Prince Akihito and Crown Princess Michiko were on a U.S. tour to commemorate the 100th anniversary of the Japan-US Treaty of Amity & Commerce and took part in a formal ceremony at the Seattle Japanese Garden. On October 5th of that year, the Crown Prince planted a Mt. Fuji flowering cherry tree (Prunus serrulata ‘Shirotae’), symbolizing Japan, and the Crown Princess planted a white birch (Betula pendula), a symbol of her family.* The birch tree has remained healthy, and many decades later still stands, prominently located on the Garden’s west side, next to the pond and the teahouse garden (roji). 

Unfortunately, flowering cherries are shorter-lived trees. The cherry planted by the prince in the Garden’s orchard area died in 2003, and the next year a tree propagated from a cutting of the original tree was planted in its place. More recently, the orchard area was completely renovated. All but one of the flowering cherry trees were replaced in December 2023 by large specimens of more disease-resistant cultivars, ‘Accolade’ and ‘Snow Goose’. 

The genus Betula: 

The genus Betula includes many species of deciduouos trees and shrubs native to the temperate and boreal (subarctic) zones of the Northern hemisphere. Their cool, moist native habitats include woodlands, stream banks and lakeshores. They are also commonly cultivated in gardens and landscapes, growing best in sun or part shade and in moist, acidic, well-drained soils. Many ornamental cultivars have been developed for attractive leaf color, leaf shape and/or habit of growth. 

The word betula is the Latin word for birch tree. 

The Betula pendula planted in October 1960 by Japan’s Crown Princess Michiko. (photo: Mary Ann Cahill) 

Betula pendula: 

Our Garden’s tree is Betula pendula, a birch species native to Europe and central-northern Asia. Well adapted to cold climates, and a major forest species in the boreal zone, it’s an important source of hardwood in Europe’s northern countries. Common names are silver birch and European white birch. Although not native to North America, silver birch has been widely planted as an ornamental in the northern United States and Canada. 

Betula pendula  is a graceful, medium sized tree that generally grows 30 to 40 feet tall (sometimes much taller) and about half as wide. When young, trees have a narrow, pyramidal habit, but with time they develop more oval, rounded crowns. Although the trunks are upright, the side branches are gracefully weeping or “pendulous”—hence the species word pendula.  Our Garden’s tree has been consistently pruned to accentuate the living architecture of its branching and to keep its size appropriate for its position next to the pond. 

The glossy green leaves of silver birch. (photo: Mary Ann Cahill)

Like paper birch (Betula papyrifera), European white birch is renowned for its showy white bark. The bark of young twigs and branches is a golden brown, but it matures to silvery white with black markings. As trees age, however, the bark at the base of their trunks becomes furrowed and blackish gray. Their glossy green leaves are simple, wedge-shaped, coarsely toothed, and about 2 ½ inches long, with tapering tips. Fall color is an unexceptional greenish yellow. 

In early spring tiny male and female flowers appear in separate catkins on the same tree. The male flowers, which release pollen, are held in yellowish-brown, drooping catkins (about 2 ½ inches long). The female flowers are held in smaller, greenish, upright catkins (about 1 ¼ inches long). After fertilization, the female flowers mature by late summer to drooping cone-like fruits with many small, winged seeds.

Betula pendula is extremely cold Hardy to USDA Zone 2 (minimum temperature -50 degrees Fahrenheit) and performs best in northern climates with cool summer temperatures and moist, well-drained soils. Easily stressed by summer heat and humidity, it will likely respond poorly to the realities of climate change. In addition, silver birch is one of the most susceptible birches to the bronze birch borer, which frequently kills the trees it attacks. Aphids, birch leaf miners, and birch skeletonizers are also problematic, as is leaf spot disease. 

Homeowners are frequently attracted to this showy, graceful tree, but without conscientious maintenance it is often short-lived. Critical requirements are moist, well-drained soil and a carefully chosen location on the property where it’s planted. To grow well, the leaves require full to part sun, but the tree’s shallow root system requires cool, moist, shady conditions. Thus, it’s best to site silver birch on the north or east side of a house or other structure, where its root system will be shaded from the afternoon sun. It should not be located next to large expanses of pavement, which produce reflected heat. On larger properties, other trees may provide the recommended shading. In the summer-dry climate of the Pacific Northwest, silver birch requires consistent irrigation until the return of fall rains. Moreover, if spring rainfall is insufficient to support its emergence from dormancy (as in spring 2024), irrigation will be required at that time as well. 

Here's a major caveat: when a relatively small tree is desired, Betula pendula should never be planted! Cutting back the thick trunks of this graceful tree, known as “topping,” destroys its beauty and opens it up to insect and disease problems. It also stimulates the rapid growth of upright “water sprouts”, so the tree grows faster and taller than it otherwise would. Fortunately, many cultivars are available, including plants with yellow or purple leaves, a dwarf or entirely weeping habit, or attractive cut-leaf foliage. 

I’m encouraged that this graceful, historic tree has grown well in the Seattle Japanese Garden for over sixty years. I hope that it will continue to do so for many more! 

* The emblem on Crown Princess Michiko’s personal seal may have been Japan’s native white birch, Betula platyphylla var. japonica.  

Corinne Kennedy is a Garden Guide, frequent contributor to the Seattle Japanese Garden blog, and retired garden designer.