Protecting our Venerable Weeping Japanese Cherry Trees

Two weeping Japanese cherry trees (Prunus itosakura Pendula Group) stand along the roadway outside the National Herb Garden. Among the Arboretum’s oldest flowering cherries, this majestic pair was planted some time in the early 1950s. For nearly three-quarters of a century, Arboretum staff have tended to the trees. Half a world away, the Japanese have over many centuries developed arboriculture techniques that are markedly distinct from Western approaches. In March of 2023, the U.S. National Arboretum invited Kurato Fujimoto, one of Japan’s leading authorities on these traditional tree care methods, to Washington, DC, to help us install tsurazue, or crutches, to support these two special trees as they approach the end of their first century of life. This is one of the first, and certainly the most public, installation of Japanese crutches in the United States, an experiment fitting for the U.S. National Arboretum.

These weeping cherries are beginning to feel their age. As the years have passed, they’ve lost several large limbs. As the trees have struggled, arborists have cared for them in the most rigorous manner possible, following established best practices in arboriculture as developed in the United States. Two frequent techniques have been pruning and cabling. Pruning removes damaged and dying branches. This allows the tree to focus its energy on growing the stronger, healthier parts of itself closer to the trunk and proactively removes limbs that might break off violently and damage healthy tissue. Weak or structurally vulnerable limbs are sometimes cabled: a metal cable is bolted both to the at-risk branch and to a sturdy, healthy branch or the tree’s truck. The tree can help hold itself up via these cables. And while these interventions have stalled the trees’ decline, they have not stopped it. In fact, the last decade and a half or so has been particularly hard on the trees. We had reached the end of what we could do to care for these trees in the methods we were familiar with.

And, so, being the scientists we are, the Arboretum decided to undertake an experiment. We had learned about Japanese cherry trees that were thousands of years old, tended to by generations of caretakers and cherished as wise, old loved ones. When the opportunity arose to learn some of the Japanese’s techniques, we seized it. These trees would become living experiments that our staff, other tree care experts, and all Americans could learn from.

Reverence for both the natural world and for old age are deeply embedded in Japanese culture. Just as bonsai are cared for, carefully and patiently, for generations, a similar attitude is extended to trees planted in the landscape. Japan’s oldest cherry trees, The Three Great Japanese Cherry Blossom Trees, are each over a thousand years old. In Yamanashi Prefecture, Yamataka Jindai-zakura, almost certainly the oldest cherry tree in the world, has grown for two millennia. Clearly, the Japanese know something about keeping venerable and vulnerable trees alive.

Japanese methods emphasize the preservation of a tree’s canopy. A tree’s leaves are how it eats. Each leaf is busily photosynthesizing, converting sunlight and carbon dioxide into sugar. Maintaining as large a canopy as possible means maximizing the amount of energy the tree can create for itself, so lightening the load of very large or old branches the tree may not be able to support on its own is a priority. In Japan, a variety of physical supports are used to prop, cradle, and shelter vulnerable trees. These techniques are quite different from those traditionally employed in United States arboriculture. Given that western approaches are well-documented in this country and used extensively elsewhere on the Arboretum’s grounds, these two weeping cherries are a unique opportunity to present a Japanese approach.

We invited Kurato Fujimoto, a master gardener and expert in Japanese tree care techniques, to come to the National Arboretum and teach us how to care for these two cherry trees in the traditional Japanese manner. Over the course of a week in March 2023, Mr. Fujimoto led a team of Arboretum staff, undergraduate and graduate students from the Illinois Institute of Technology and Cornell University, and colleagues from Dumbarton Oaks; Hillwood Estate, Museum and Garden; the Chicago Botanic Garden, and Pennsylvania State University in fabricating and installing 18 crutches to support the pair of trees.

Our trees are settling in nicely with their new supports, and we like to think they’re enjoying the opportunity to rest their achy limbs. They will continue to be cared for in this manner in perpetuity. Only time will tell how they’ll respond to their new braces, and the public will learn right alongside us as the years go by. Please be sure to visit them whenever you are at the Arboretum and monitor this living, cross-cultural experiment!

The project team at week's end.
The project team at week’s end.