Bonsai specialist Jun Imabayashi explains the nuances of repotting centuries-old living artworks.

At the mention of an upcoming meeting about repotting bonsai at the Arnold Arboretum, a friend expressed confusion. “What’s so important about the pot?” they asked. Groping for an answer, we replied that many of the plants in our bonsai collection are centuries old; repotting them is like choosing a new frame for an Old Master painting.

What’s so important about the pot? Confronting this question, Jun Imabayashi, the arboretum’s bonsai specialist, goes back to basics. He points out that bonsai essentially means “pot” or “potting” in Japanese (bon “tray” + sai “planting”). Long-lived trees in vessels—this is the very magic of bonsai, the basis of the wonder it engenders in us. Thus like a fine painting’s frame, the pot needs to match and support the character of the tree. Of course, some of that character is fixed, but some of it is ever-changing, as the plant grows and senesces, ebbs and flourishes, over a lifetime that can encompass centuries (some trees in the Arnold’s bonsai collection approach 300 years old). At the same time, the essential role of the vessel in the art of bonsai transcends both etymology and aesthetics. For the pot is a vessel for living in; it must support the plant’s flourishing and growth. In this sense, the analogy to frames and rare paintings is inadequate—for in the case of bonsai, the work of art is ever-changing, the masterwork ever repainting itself.

Aesthetics do govern the process, however. Every tree needs a face, a front, Jun explains; it might want to be placed off-center in the pot for the sake of balance, to create negative space. “It’s not like a flower arrangement, to which you’re just adding adding adding,” he says, his hands stuffing imaginary herbaceous material into a vase. “With bonsai, we mostly are taking away.” As material is taken away, he explains, more of the tree becomes visible.

There are rules of thumb, too: deciduous trees want a shallow pot that is round or oval; the conifers often like to show off in tall, angular containers. For display, a tree will be dressed up in a special pot, often very shallow. And yet the plant will need more watering and attention in such shallow pots. Thus, for long-term care and display, Jun prefers to go one size bigger than he might otherwise choose.

Jun also tries to match old trees with vessels of commensurate age. Pots don’t grow, but they do age, Jun points out, and so it’s important to find pots with patina to match the venerable glamor of the trees. Such patina can be subtle. Jun shows off one pot he picked up on a recent trip to Japan: with a volume of perhaps a gallon—not much larger than an old-fashioned desk phone—the vessel is pentagonal in cross-section, with a handsome, rolled lip and gently scalloped feet at the corners, its soft, unglazed taupe color seeming to dissolve into itself. When Jun saw the pot, he immediately thought of a particular hundred-year-old juniper at the Arnold. He carried it back to the U.S. in his luggage.

Repotting a centuries-old bonsai is like choosing a new frame for an Old Master painting.

For all the importance of pots, their provenance is not tracked, although the arboretum does keep the original pots in which trees arrived. They might prove useful again as the trees grow into and out of new shapes and relationships. Repotting is more than an automatic affair, as it combines aesthetic consideration with the needs of plant health. As such, it mostly happens in a narrow time frame in spring, coincident with the beginning of the trees’ most active growing season.

Repotting can facilitate this growth or hamper it. It’s a delicate time. The week after repotting is most crucial, as Jun and colleagues mist, water, and feed the plant with special care. If the pot doesn’t work out, Jun will wait until the next year to try again—to repot again would put the plant under too much stress. “With a surgery, people think of the operation in the hospital as the hard part. But after the operation, you still must stay in the hospital,” Jun points out.

In the shed where the bonsai overwinter, Jun turns to a low shelf holding the original pots in which some of the plants arrived at the arboretum—great bowl-shaped vessels of caramelly terra cotta the size of truck tires, now more than a century old. These big vessels weren’t for showing off the bonsai, however, but for transporting them—the pots are too big for permanent display, but were probably sized to protect the plants in transit. Indeed, they’re too big for long-term use—with the greater soil volume of a large pot, it can be difficult for the soil to warm up to temperatures optimal for the health of the plant.

Jun points out that often, collectors and enthusiasts are in a hurry to achieve a specific visual effect with a tree, which they want to fix in perpetuity. “But the trees are alive,” he points out; “supposedly, this is just the beginning” of a long process of changing and unfolding form. Traditionally, changes happen slowly, over years and years, and successive repottings unfold in the rhythm of the tree’s long-term relations with collectors, connoisseurs—and foremost, with caregivers. Jun is mindful of his relationship with past bonsai artisans at the Arnold, who collectively have tended the trees for more than a century. He muses too on the long lives of the plants themselves—and the way they have always been entwined with people, through good times and bad, times of war and displacement. Through it all, Jun notes, people cared enough about bonsai to keep them, protect them, nurture them—and move them to safer ground, even over oceans. The vessels these plants have seen are varied indeed.

Jun Imabayashi is the bonsai specialist for the Arnold Arboretum. This essay is drawn from conversation with Jun, whose remarks have been condensed and edited for publication.

From “free” to “friend”…

Established in 1911 as the Bulletin of Popular Information, Arnoldia has long been a definitive forum for conversations about temperate woody plants and their landscapes. In 2022, we rolled out a new vision for the magazine as a vigorous forum for tales of plant exploration, behind-the-scenes glimpses of botanical research, and deep dives into the history of gardens, landscapes, and science. The new Arnoldia includes poetry, visual art, and literary essays, following the human imagination wherever it entangles with trees.

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