Bonsai collection highlights age, beauty

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Harvard’s Arnold Arboretum specimens hundreds of years old

The foliage is green and youthful, but the twisted, gnarled trunks show the trees’ age. But that’s the point, of course.

Straddling the boundary between art and science, the Arnold Arboretum’s striking bonsai collection reaches back into history, to a time when shoguns ruled Japan. The collection’s oldest tree, a hinoki cypress, was first cultivated in 1737, 270 years ago and more than a century before the last shogun handed power to the emperor.

The collection, which numbers about 40 trees, including recent additions from China and Japan, got its start in 1913, when U.S. Ambassador to Japan Larz Anderson brought 39 trees back when the Taft administration ended.

When Anderson died in 1937, his widow, Isabel, donated 30 trees to Harvard. The remaining nine were donated 12 years later, after her death.

The collection has withstood the ravages of time, but not without losses. A lack of knowledgeable bonsai gardeners in the decades after the collection’s acquisition resulted in the loss of several plants. The 15 plants remaining in the Larz Anderson Collection, cultivated in this country longer than any other bonsai, form the core of the Arboretum’s larger bonsai collection.

Beginning with the tenure of curator Connie Derderian in 1969 and continuing under the current curator, Peter Del Tredici, the collection has been revitalized, with the plants receiving the daily watering, intensive pruning and meticulous shaping that bonsai demand.

Don’t ask Del Tredici which bonsai is his favorite, though. After more than 20 years tending the plants, selecting one would be like parents picking among their children, Del Tredici said. Each plant has its own characteristics, standing out at a different time of year: during springtime flowering, the summer’s long days, or when the foliage finally turns and winter’s cold storage looms.

“These are like my kids. I’ve been taking care of them forever,” Del Tredici said.

The collection is housed at the Arnold Arboretum, where Del Tredici is a senior research scientist. They go through an annual cycle of care demanded by the constraints of growing what are normally large plants in small containers. Roots are trimmed early in the spring to prevent girdling that could strangle the plant in the pot. Pruning of the foliage occurs later in the spring after the first growth, and for some plants a second time in the summer, along with wiring the branches into desired shapes. In these tasks, Del Tredici collaborates with Colin Lewis, a British bonsai master who has been working with the Larz Anderson Collection for more than five years.

The regular pruning of the bonsai roots actually helps the plants reach such a great age by slowing down the aging process, Del Tredici said. The collection’s plants are repotted every two to five years, depending on the size of the container they’re in.

Since the region’s freezing winters can damage plants kept outdoors in containers, the collection is brought into a cold storage facility each winter. The plants are kept at temperatures just above freezing but cold enough that they go dormant and can be kept in the dark without harm.

Del Tredici said the growing season has lengthened in recent years. The collection used to be brought indoors annually on Veterans Day. This year they were brought in just before Thanksgiving. Similarly, he said, they used to be brought out on Patriots Day and in recent years they’ve been moved out a week or so earlier.

Though the shapes of the older trees have long been established, they still require intensive maintenance, Del Tredici said, including wiring and pruning.

“It’s all about the care and attention, particularly with respect to shaping,” Del Tredici said. “You have to constantly prune them or they’ll stop being bonsai, even the old ones.”
Harvard’s Arnold Arboretum

The grounds are open from sunrise to sunset every day of the year. During the cold months, however, the bonsai collection is put in storage and, therefore, is not accessible to the public. The collection returns to its outdoor structure, which is located between the Dana Greenhouses and the Leventritt Shrub and Vine Garden, in mid-April. An interactive map of the grounds can be found at For general information, visit