A conversation with Piet Oudolf on Philadelphia’s new Calder Gardens
The Dutch landscape designer is revered for his use of colour, form and texture that transcends seasons. Now, he’s turned his hand to Calder Gardens in Philadelphia, a new art institution in the birthplace of acclaimed artist Alexander Calder

Detail of a sketch by Piet Oudolf for the Calder Gardens, Philadelphia. Courtesy of Piet Oudolf.
Philadelphia’s new Calder Gardens redefines the art-viewing experience by uniting architecture, nature, and the groundbreaking work of Alexander Calder. The museum, which opened on 21 September, functions as a living, breathing environment with a rotating selection of artworks spanning Calder’s entire career. The architecture firm Herzog & de Meuron designed the 18,000-square-foot building, while the extensive gardens were created by renowned landscape designer Piet Oudolf. Celebrated for his perennial-forward designs that embrace the seasonal life cycles of plants, Oudolf has designed gardens for New York City’s High Line and Battery Park, amongst others. He recently sat down with Christie’s to discuss his vision for Calder Gardens as a growing and changing site for great art.
How did you become involved in Calder Gardens?
Piet Oudolf: I met Sandy Rower [Alexander S. C. Rower, Calder’s grandson and president of the Calder Foundation] for the first time at Hauser & Wirth in England. He told me he loved my work and wanted me to come to America to see what I could do for a garden. I think the Calder Garden was already in his mind, but he did not share the idea with me then. When I finally visited him — this was around 2022 — I understood he wanted me to work on Calder Gardens specifically. We’ve worked several years on this, and I think it has worked out very well.
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More than 250 varieties of plants make up the gardens conceived by Piet Oudolf for Calder Gardens, where Alexander Calder’s work is displayed both outdoors and inside an 18,000-square-foot building designed by Herzog & de Meuron. Rendering by bloomimages, © Herzog & de Meuron. Artwork by Alexander Calder © 2025 Calder Foundation, New York / Artists Rights Society (ARS), New York
Does the garden represent your initial vision? Plants are living specimens — do plans ever turn out differently than expected?
PO: At the start, you only have an abstract vision. You know the conditions, the site, the architect’s building, but you haven’t yet been there in person. You start imagining what could be done — especially when it’s not one garden but a series of spaces, each with a different mood. A lot changed along the way — architectural elements, fences, pathways. You always wait for a ‘final’ master plan, but in practice, it never stays the same. You have to stay flexible.
Tell us about the different ‘concept’ areas within the garden.
PO: On both sides of the garden, there are small woodland areas, ‘garden concepts’, ideas that make each part of the garden feel unique. So, from some entrances, you don’t see the full garden at once. You walk through woodland and then the garden opens up into different types of plantings. There’s a perennial garden we call the ‘robust borders’ and another we refer to as a ‘matrix’ or meadow-type planting, especially around the entrance. Each space offers a different experience.
Oudolf’s diagram of plant species within the Woodland East section of Calder Gardens gives insight into the landscape designer’s process
Oudolf creates maps and drawings with rigorous keys that detail each species in his perennial-driven designs
Is the garden designed to be explored in a specific direction, like a pathway through a museum, or is it best suited to wandering exploration?
PO: There are three entrances from different streets, so there are many ways to explore. It’s not linear. Your experience will vary depending on how you arrive.
You’re known for creating gardens that evolve year-round. How did you approach that here?
PO: Yes, I always design for year-round interest. We begin with bulbs in early spring, then woodland plants and ephemerals. The more traditional perennials — what I call ‘open sky’ perennials — come later in May and June. The woodland gives you early spring bloom and then transitions to other areas as the seasons change. That way, the garden evolves over time, and no single area dominates the entire year.

Calder Gardens, 2025. Photograph by Iwan Baan. Artwork by Alexander Calder © 2025 Calder Foundation, New York / Artists Rights Society (ARS), New York
Were there considerations around how sculpture would integrate with the plantings?
PO: The sculptures don’t really sit within the plantings. They’re in designated spaces — like the entrance and sunken courtyards beneath the museum’s main level. We’ve designed planting to interact with the walls around those spaces—covering them with plants that hang over or climb up. Great art always fits into a well-designed garden.
You've worked with Herzog & de Meuron many times before. What was different about this site?
PO: This time, the garden plays a very central role — it’s not just surrounding the building but helping define it. The building is revealed slowly as you walk along the woodland paths. It’s about creating a sense of discovery. The garden doesn't embrace the building so much as it puts it on a stage.
Do you approach designing for public institutions differently than private residences?
PO: Yes. In a private garden, especially if the owner loves plants, you can take more risks, like using plants that may not live long but can be replaced. In a public space, you need reliability, plants that will last many years. You also rely on full-time gardeners. The long-term care is very important.

A top-view diagram of every species in Calder Gardens with walking paths and open areas for sculpture. Illustration by Piet Oudolf
Speaking of long-term care, how do you envision the garden evolving over the next five, 10, or 20 years?
PO: A perennial garden might last 20 years, then you replant. Look at the High Line — opened in 2009, still working beautifully. Or the Lurie Garden in Chicago — 20 years old this year, and we’re just now starting to make some changes. Over time, trees grow, roots expand, and things must change. But with good gardeners who understand the design, the spirit can continue even if the details evolve.
Alexander Calder himself was fascinated by plants and even named some of his works after them. Did that influence your planting choices?
PO: No, I don’t do much research like that. It’s the opposite of what architects do. I trust my instincts — what feels right for the place, for the time we live in. My goal is to create something that is my own but resonates with others.

‘If everything works — the art, the building, the garden — this will be a place people remember. Like the High Line, it will become a destination,’ says Oudolf of Calder Gardens, nestled in the center of downtown Philadelphia. Photograph by Iwan Baan. Artwork by Alexander Calder © 2025 Calder Foundation, New York / Artists Rights Society (ARS), New York
Garden versus museum—how does the name change a space’s spirit?
PO: Sandy insisted this be called Calder Gardens, not a museum. That’s rare. It’s a statement. A garden is always growing and changing. A museum can be more static or historical. A garden might become historical too, but mostly in photographs. If everything works — the art, the building, the garden — this will be a place people remember. Like the High Line, it will become a destination.
Did Philadelphia’s climate and geology impact your plant selection?
PO: Yes, of course. It’s milder than Chicago, softer than New York. I could use my full plant palette here — no limitations due to extreme cold. I’m very curious to see it all in full bloom next year. I believe it will be a very special place. If it’s well cared for, it will thrive for a long time.

Calder Gardens, 2025. Photograph by Iwan Baan. Artwork by Alexander Calder © 2025 Calder Foundation, New York / Artists Rights Society (ARS), New York
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