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Microbes Beget Elegance

Posted On May 31, 2019 | 09:42 am | by ostmannj01 | Permalink
Ellipse garden thriving after soil restoration, replanting, and renovation

By Julia Ostmann

On a cold day in January, hatchets, chainsaws, and clippers descended on the Dumbarton Oaks Garden.

They had come for the Ellipse: a double ring of trees whose branches and leaves meld together, forming a hedge floating high off the ground. Scattered benches and a large stone fountain complete the picture. “It’s a really restrained, elegant space,” says Jonathan Kavalier, director of gardens and grounds.

But the trees were dying. Since their planting following a redesign by Alden Hopkins in 1958, nearly half of the Ellipse trees had been removed, their roots often shriveled to almost nothing. Five years ago, former garden director Gail Griffin launched a plan to restore the Ellipse, arranging for a Maryland nursery to grow almost 100 new trees.

renovation quad
Several months of transformation this winter and spring restored the Ellipse to new health and a hopefully more sustainable future (photos: Elizabeth Muñoz Huber)

What was killing the trees? Searching for a culprit, Kavalier conducted diagnostic testing with renowned soil expert Eric T. Fleisher, who restored and revamped soils at Harvard University, the Chicago Botanic Garden, the Museum of Modern Art, Storm King Art Center, and more.

Fleisher found a dense, compacted soil with almost no life. Not even earthworms wriggled through, much less the large quantities of beneficial bacteria and fungi that contribute to important nutrient cycling.

“So many people focus on the chemical and textural makeup of the soil. We’re also focusing on the biological makeup, the life of the soil—bringing life back to the soil so it does what it has to do,” said Andrea Filippone, a partner with Fleisher in the firm F2 Environmental Design.

Soil experts Eric Fleisher and Andrea Filippone
F2 Environmental Design, headed by Andrea Filippone and Eric T. Fleisher, consulted on restoring beneficial microbes to the soil and developing a sustainable soil mix (photos: Elizabeth Muñoz Huber)

For the new trees to last 100 years, not just a few decades, they would need new soil. Fleisher set about designing a custom mix. A generous donation from local philanthropist and Ellipse lover Lee Folger made the entire project possible.

Meanwhile, it was time to take down the ailing trees. A team of contractors, including two former Dumbarton Oaks gardeners, tackled the project. Sean Lowrey remembered trimming the Ellipse more than 10 years ago, concerned that some of the trees were sickly. “If anyone is going to take down these trees, it’s me!” he said. The old trees produced some 24 yards of wood chips, which were saved so they can be incorporated into the kitchen garden pathways.

Then it was a race against time to mix the new soil. Winter rains and frozen temperatures could ruin days of work, and the soil needed to be installed by spring, when the particular tree species (American hornbeam) can safely be transplanted from the growing nursery.

After garden staff salvaged useful components of the old planting bed soil, Fleisher trained them in mixing a healthy recipe of silt, sand, old soil, and new local compost. Staff learned how to tell when the soil mixture is just right: it should compact into a snowball-like shape, then easily fall apart into crumbs at a gentle touch. They also studied how to make compost tea, a liquid superconcentrated in microorganisms, to apply to soil.

In total, more than 25 people worked on the Ellipse renovation, from garden staff to contractors to the Maryland nursery to a local farm where new soil components were sourced. Dumbarton Oaks gardeners gained skills they plan to use in other areas of the garden, such as the roses and the Box Walk.

Jonathan Kavalier and Kim Frietze
Director of Gardens and Grounds Jonathan Kavalier and gardener Kim Frietze survey the Ellipse renovation. More than 25 people worked on the project (photos: Elizabeth Muñoz Huber).

Finally it was time to plant the new trees. But a new wrinkle emerged: how would the team preserve the intricate design of the space, beyond just improving the health of the soil?

Pioneering landscape architect and Dumbarton Oaks garden designer Beatrix Farrand originally envisioned the Ellipse as a space that would appear symmetrical and balanced. (For more about the design history of the Ellipse, read this recent article by Kavalier.) “When you walk in here, you feel equilibrium. You feel a balance,” says gardener Kim Frietze.

Fountain, then and now
Beatrix Farrand originally designed the Ellipse garden with a two-tier fountain pool and boxwood hedges surrounding the space. This archival photo probably dates to 1955–1957, just before Alden Hopkins redesigned the space. More alterations occurred in the 1960s, and today American hornbeam trees and a Provençal fountain greet Ellipse visitors (photos: Dumbarton Oaks Garden Archives and Elizabeth Muñoz Huber).

So before the old trees were removed, Frietze took meticulous measurements of each tree’s placement. The new trees were planted within one inch of where each old trunk had stood.

With freshly planted lawn, fountain burbling, and 76 young American hornbeams standing proud in the sunlight, the Ellipse reopened in April. The Washington Post featured the renovation project in its pages. The aerial hedge will reform over the next few years as the trees grow—the start of what is hopefully a long, healthy life requiring minimal chemical inputs, thanks to the new soil mix.

But months of renovation have done nothing to change the Ellipse as one of the most welcoming spaces in the Dumbarton Oaks garden. So welcoming, in fact, that a snapping turtle has already taken up residence on the fountain’s edge.

Then and now
Over many decades of design changes and renovations, the Ellipse has always beckoned to visitors, welcoming them into an elegant space of balance and tranquility (photos: Dumbarton Oaks Garden Archives and Elizabeth Muñoz Huber)


Julia Ostmann is the postgraduate writing and reporting fellow at Dumbarton Oaks. Elizabeth Muñoz Huber is the postgraduate digital media fellow.