A Conversation with Andi Pettis, Director of Horticulture at Governors Island
“We have declared 2024 the year of milkweed,” says Andi Pettis, director of horticulture at Governors Island. For the past couple of years, Pettis and her team have been busy incorporating milkweed into the island’s plantings. They’re focusing on the three species native to the ecoregion: butterfly weed (Pettis’s favorite because of the “incredible variation in color from golden yellow to almost scarlet”), mauvy common milkweed, and hot pink swamp milkweed. Her goal is to finish planting 5,000 plants this year. “Showing the relationship between monarch butterflies and milkweed is an easy way for us to connect people to the benefits of native plants and show them why it’s important to support wildlife even in an urban environment.” The efforts have paid off. They’ve been noticing more and more monarchs on the island. You’ve heard it before: If you plant it, they really do come.
But planting milkweed is just one of the many initiatives that Pettis and her team are doing to bolster biodiversity. “Climate resiliency and sustainability were sort of baked into the design of the park,” she says. Created by the design firm West 8, with Mathews Nielson Landscape Architects, the park features 120 acres of hills, meadows, and forests in the middle of New York Harbor. “It was a reuse project really—an old military base turned into a public space with new parks,” she said. “But there was no horticulture staff when I was hired.” Pettis, who trained at Brooklyn Botanic Garden, rose through the ranks at The High Line to become director of horticulture before moving to Governors Island almost six years ago, had to build a team from scratch and start rehabilitating areas where maintenance had been deferred for years. Today, she and her team have introduced 52 native plant species to the island, planted habitat for butterflies and birds, and brought in sheep to tame the rampant spread of invasive species. “We’re working with nature here,” she says. “It’s not a short fix, but it’s working. We’re in this for the long haul.”
Pettis talks about this bustling and beautiful urban island park and shares how they’re bringing biodiversity back.
According to Xerces Society for Invertebrate Conservation, Eastern Monarchs have suffered an 80% decline in populations. Governors Island is doing what they can to help reverse this trend by planting milkweed, the monarch’s main food source, on the island. Here, in the milkweed demonstration garden in Liggett Terrace, several different pollinator-friendly native plants grow together including butterfly weed (Asclepias tuberosa), swamp milkweed (Asclepias incarnata), anise hyssop (Agastache foeniculum), ‘Jeane’ garden phlox (Phlox paniculata ‘Jeana’), and ‘White Swan’ coneflower (Echinacea purpurea ‘White Swan’). Photo by Sarma Ozols.
How are you gardening for biodiversity?
The park was designed for sustainability and climate resilience. West 8 built hills and these kinds of swales and berms to raise part of the park out of the 100-year floodplain. Working with Matthews Nielsen, they created a lot of naturalistic areas based on coastal maritime plant communities and filled the park with a lot of native trees. I think there are 53 different species of native trees planted on the South Island alone! We are really holding those tenants dearly as we move forward.
We have made it clear that we are choosing plants that mimic our coastal maritime shrublands and grasslands native plant communities. We’re also focusing on those that benefit biodiversity and wildlife. In areas where we have managed to retake the land with these native plant communities, we’ve seen huge upticks in the native insect populations.
In late summer and fall, common milkweed (Asclepias syriaca) produces seed pods as seen here in the Fort Jay Meadow. Photo by Sarma Ozols.
How are you adapting to our changing climate?
As temperatures warm, we are definitely experimenting with plants that would be considered more Southern. For example, we are considering planting live oaks on the island. We are also growing pawpaws, persimmons, and magnolias that are all doing really very well.
During the pandemic, we decided to stop mowing one of the areas around the historic forts. It was originally a golf course. When I began here at Governor’s Island, we were essentially mowing it as a manicured lawn. But when we stopped, people loved it, so we just mowed paths and areas under the trees where people could picnic. The area became very experiential. We loved seeing people walking through the meadow and using the land in a very different way than it had been intended. We also saw the populations of insects pick up. We could hear the buzzing of pollinators and watch ground nesting birds using that habitat every spring. While there are some native plants there, it’s mostly cool season European turf grass that we let go. Of course, mugwort has started to take over in areas. The ground nesting birds don’t mind because it’s still a useful habitat for them. But we realize just how much more valuable the land would be for all wildlife if it were a native grassland, so we are now working to restore that area to native grasslands and create important habitat.
When you walk along the pathways on the 70-foot high Outlook Hill, you’re immersed in plants like the fragrant native shrub Clethra alnifolia ‘Ruby Spice’ (right) and the red fruiting Viburnum opulus (Guelder-rose). Photo by Sarma Ozols.
What are some of the ways you’re handling invasive species?
When I started at the park almost six years ago, maintenance had been deferred on the new parts of the park for probably five years. As a result, a lot of those naturalistic areas that had been planted with native plants had failed and had become monocultures of mugwort and phragmites. It was a huge challenge trying to get rid of them and we’re still at it.
Mowing and Hand-pulling
We tried mowing, thinking that we could deplete the energy of these plants, but that did not really work. We also tried hand pulling, but, of course, both phragmites and mugwort spread by rhizomes, so pulling is really a Band-aid fix. We would have hundreds of volunteers come out at a time and pull. It would look great for a couple of weeks, but then the mugwort would come right back.
Sheep
Then, one of our gardeners at the time, Malcolm Gore, was sort of exhausted by the whole process, asked, why don’t we get sheep to come in and graze? And so, we were like, yeah, why not? Let’s give that a try and see what happens. We decided against goats because the area where we were proposing this experiment was essentially a young urban forest with lots of young woody plants, which is what goats prefer. Sheep, on the other hand, love soft vegetation. I think the first season we had sheep on the island, we saved Malcolm alone 800 hours in mowing compared to the year before—and the huge carbon footprint that comes with mowing.
After the sheep graze the mugwort and phragmites in an area, we rotate them to another spot and plant the grazed area with native plants. Slowly we’ve been able to create an understory in this young urban forest. Four years later the sheep are still coming. They return every season, usually from mid-May to mid-September. After they’re done here, they go back to Friends of Tivoli Lake and Preserve and Farm until next year. We’ve had an amazing partnership with them.
Evening, one of the five seasonal landscaping sheep brought in to help control invasive species, pauses for a photo in Hammock Grove. Photo by Julienne Schaer.
Solarization
As the sheep project was happening, we started looking at the hills [Discovery and Outlook, in particular]. Since these areas are mostly in full sun, they require a different management technique than sheep. For our first trial, we solarized about 1,200 square feet and have gone up from there. We’ve probably solarized more than 5,000 square feet in total. We work in patches, and have been able to re-establish native grasses, shrubs and forbs [herbaceous flowering plants] in those areas and have created some really beautiful meadows, grasslands, and coastal shrublands.
We have found that clear plastic works best for us with our conditions. We dig a trench around the area we want to solarize, which keeps the rhizomes from surrounding invasive species from crawling back in. Then we lay down plastic, weigh it down, and leave it up ideally April through September. We can come back in October and plant. We found that planting a combination of plugs and quart-sized pints and then seeding over them with cool and warm season native grasses has worked really well.
While solarization works for smaller patches, it is not really a scalable method to manage these invasive species for us. Our hills are massive. We are now working with Larry Weaner Landscape Associates to design trial transects and plant palettes that we can grow from seed and plugs in these massive areas. Again, it’s not a short process. We’re probably looking at five to seven years to figure out what will work, but we’re hopeful.
Please talk about the trees on Governors Island.
We have a lot of mature trees in the North Island, including an American elm that’s about 200 years old. It’s probably survived because we are on an island. We have a pretty diverse canopy, but many of these trees are aging. As we move forward, we have to think about not only planting for biodiversity, but we also need to plan for the age diversity of our trees. Fifty-three percent of our tree canopy is London plane trees, which were all planted during the Robert Moses era. He planted thousands of them all over New York City and now all of those trees are aging out at the same time. We are thinking about what to plant behind them.
Right now we are interplanting some of our beautiful old allées with other canopy trees, like native hickories, walnuts and oaks. These classic native trees do really well here in the North Island. One of the things about gardening and horticulture is that we are not planting these trees for ourselves, right? We will never benefit from the shade of those trees. We are planting them for our children and our grandchildren and all of the wildlife that will use that environment in the future.
How are you creating more habitat?
Let’s take Hammock Grove, which is a young urban forest that’s about seven acres filled with more than 40 native tree species. Some of the trees are planted at their southernmost range, some of them are at their northernmost range. In the original design, the area was under planted with a native meadow mix that included lots of warm season grasses and forbs [herbaceous flowering plants] to protect the young saplings and seedlings from exposure. As these trees were getting established, this meadow was meant to protect them essentially. But since we have a mix of trees from different regions, we are watching them to see which ones are thriving in our changing climate and thinking about how we can under plant them with native shrubs and shade plants.
We want to create an immersive experience for our visitors while also creating habitat in that area. We have created paths so that people can really walk through and feel like they are in a forest. We are experimenting with different varieties of shrubs, like Rubus and Viburnum, and spring ephemerals, like Aquilegia, Claytonia, and bloodroot. We’ll see what works well—and what works too well. It’s always a challenge.
On the North Island, where many buildings are landmarked. There’s a campus feel to the landscape. Coastguard families were gardening for years. There are classic garden beds planted with lilies, lilacs, and daffodils – masses of daffodils. They are workhorses that will be here forever. But as we restore planting beds in front and around houses, we’re using native plants in a more formal way. Eventually, we would like to create demonstration gardens to show how native plants can work in more formal and classic ways.
What are some ways visitors can learn more about biodiversity on the island?
We encourage people to take part in some of our community science programs. We offer monthly nature walks with City College of New York insect ecologist professor Amy Berkov. Amy will take people around with nets to explore the insects on the island. She is just a wealth of knowledge and so excited to share what she knows. It’s really fun to see people swishing a net over meadow plants and seeing this sort of amazing universe of insects that they might never have noticed or thought about before. Amy then can tell everyone more about what they’re seeing, like what a particular wasp pollinates, or what insects overwinter here, or what birds like to eat a certain insect.
She also occasionally holds night trapping sessions where she sets up a special light and a big sheet to attract nighttime insects. It’s not just moths, but beetles and other pollinators active at night. Download iNaturalist to log what you find on the island and sign up for one of these walks!
What are some areas of the park you are especially loving now?
Discovery Hill is really beautiful right now. You walk up these winding paths to the top of the road where you feel enclosed by all the native plantings. You’re surrounded by lots of grasses, like Panicums, little blue stem, Andropogon. Then there are mountain mints, Coreopsis, and Echinacea, as well as shrubs like bayberry, Viburnum, and Clethra. Then, all of a sudden, you reach the top and the view opens up. You can see New York Harbor— the Statue of Liberty, Brooklyn, New Jersey. Similarly on Outlook Hill, when you reach the top, you have a 360-degree view of Manhattan, New Jersey, Staten Island, Ellis and Liberty Islands, Brooklyn. You really feel immersed in nature, but at the same time you have this incredible view of New York City.
This interview has been condensed and edited for clarity.
by Melissa Ozawa
This is part of a series with Gardenista, which ran on August 22, 2024.
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