Life of the Tree People: Meet the Arborist, Landscape Designer and Author of “Growing Native Hawaiian Plants”

Heidi Bornhorst talks about designing a zoo habitat for elephants, using a forklift to pick up her future husband and why grass is a super alien.


Heidi Bornhurst


In our February cover story, we delve into the importance of urban trees and some of the people and organizations growing Honolulu’s urban canopy. We also explore some of the trees deemed exceptional since the state established the Exceptional Tree Act in 1975. Along the way, we spoke to many arborists—they didn’t all make it into the story, but in our online Life of the Tree People series, we explore what a life caring for trees looks like.


Heidi Bornhorst greets me in the gardens of Arcadia—in Greek mythology, Arcadia is the home of Pan, god of the forest and the wild. It’s an appropriate name: The retirement home’s urban forest is tucked away on a busy stretch of Punahou Street where sidewalk trees are routinely scarred and damaged by reckless drivers. Arcadia’s gardens are a reprieve for its residents, both human and otherwise. Manu o Kū, or the native white fairy tern, the official bird of the city of Honolulu, often lay their eggs in Arcadia’s trees—the retirement home’s human tenants have even formed a committee and see themselves as the “guardians of the manu o Kū,” says Bornhorst. “As a landscape designer, especially in the time of COVID, I think about, what do all these residents see from out their window?” She gestures at the tree canopy above. “What life is in these trees?”


In the gardens of māmaki and lychee trees and loulu palms, it’s easy to see why Bornhorst, Arcadia’s arborist and landscape designer and author of Growing Native Hawaiian Plants, loves to work here. Its history also draws her in—Arcadia was the site of the first governor’s mansion, home of Walter Frear, appointed in 1907 as the governor of the territory of Hawai‘i. Many of the original trees on the property have been preserved. In 1967, when Arcadia reopened as a retirement residence, Richard Tongg, the first landscape architect of Chinese descent in Hawai‘i, designed its gardens. Bornhorst took over Arcadia’s gardens from Paul Weissich, director of Honolulu’s Botanical Gardens for 38 years. 


I spoke with Bornhorst about her work with trees, past and present. Here’s what she had to say.


SEE ALSO: Photo Gallery: See Some of Honolulu’s Exceptional Trees


There’s an arborist rule: You never remove more than a quarter of the tree at a time. It’s actually a third, but for men, they like to cut, so I tell them a quarter. My thing is [when giving directions to tree trimmers], cut, cut, come down, look, rest and drink water. You can go back up. But if you over trim because you’re in a bad mood, we can’t paste it back.


Bad cuts are an entry for disease, and cuts that are too big. The branch has to be a big enough size that the wound can close off. We don’t call it healing because they’re not exactly like people. One of our arborist words is compartmentalization—the tree can close off that wound that we inflicted on it. Because it is a wound. Trees don’t need us to trim them; it’s a purely human construct. 


Right out of high school, I joined the apprenticeship program on Kaua‘i at the National Tropical Botanical Garden. I’ve worked at botanic gardens, Hale Koa Hotel and as a zoo horticulturist—that was my first real job. There was this evolving field of zoo horticulture—modern zoos were getting rid of the metal and cement, making naturalistic landscapes that have moats and things to keep the animals in and the people away. And the huge component of it is the plants. 


For my [job] interview, I designed a habitat for the elephants: a section of Asian native plants; a section of Asian horticulture crops, sugar cane, rice, orchids to make it pretty; and then food plants, so the whole habitat told a story, but it was also enriching the lives of animals. We grew  sugar cane, coconut, banana—oh my God, it’s so cool to watch elephants eat those. My friend, Sandi Baniaga, was working for Hawai‘i Sugar Planters. They were getting rid of all their old Hawaiian sugar cane varieties, so we went to Maunawili and got all this sugar cane and planted it at the zoo. 


Part of my botanic garden background is to plant interesting stuff, plant stuff with a story and keep records. At the botanic gardens, we have an accession book, a database of all the trees. Every plant has a pedigree. Botanic gardens are like a living tree library. I kind of re-created that at the zoo, re-created that at Hale Koa and here. 


Some people think of trees as a nuisance and rubbish. I have this saying: Only people make rubbish. Trees make mulch and compost. It’s a more holistic approach. When I went to UH it was better living through chemicals. People would say, “Oh, Heidi, you like plants, you like botanic gardens, you should be a fertilizer salesman, or you should run a golf course.” 


People are a slave to grass. Once, on a tour I was giving at Hale Koa, someone said, “Heidi, I have two questions: Do you think grass is a sentient being, and do you think it has us trained?”


I pause a minute and I think about it, and I’m like oh my God, he’s so right. People in my profession, especially the ones who work at the golf course, they get fired if the grass isn’t perfect. At the lū‘au lawn at Hale Koa, there’s special fertilizer, a different fertilizer in winter, special lawn mower, soil amendment. And then me, fighting with the setup guys: “Don’t dump poi, don’t dump ice on the grass!” That lawn grass is not natural in Hawai‘i. It’s pretty, it’s functional, the kids can play on it. But the modern way we do grass with weed eaters and herbicides is detrimental to trees. Grass is a super alien.


SEE ALSO: How the Arcadia Family of Companies Copes with COVID-19


My husband and I met at Foster garden. He worked for the landscaper that was planting all of our trees and grass at Ho‘omaluhia. I was the botany clerk. I’m growing all the plants, I’m keeping track of everything, all my little babies. One day, he comes in with the forklift to move the trees in 50-gallon drums, and I think, oh this guy is kinda cute. I say to him, “Can I learn how to drive a forklift?” That’s my pickup line. I was a really good forklift driver, and then he invited me to a Cazimero May Day concert.


Favorite trees—I love rainbow shower trees. We have some amazing ones here. (One of Arcadia’s rainbow shower trees was propagated from Hawai‘i’s original rainbow shower tree.) They’re a made-in-Hawai‘i hybrid. Rainbow showers are like a mule—they’re sterile. They flower nine months out of the year and are fragrant in the early morning. They don’t have a lot of seeds to contend with and are really tough and drought tolerant. 


My other favorite is lychee trees; we have a tall one here (at Arcadia). 


As a little tiny girl, I’d watch this big banyan [in our yard] and the birds and I’m like, “Mom, I think trees make the wind.” And they don’t, but they do. It’s not a cosmic thing. Trees, they pull up water from their roots and they off-gas water vapor and oxygen out of their leaves. So the climate around a tree is cooler, it’s more oxygenated. When you get a storm, the leaves slow down the rain. The roots catch the water. Trees and plants percolate the water so it goes in our aquifer. Doing trees correctly, doing gardens with minimal pesticide and reusing leaves—it’s all a benefit to our planet, our health.



Before I leave, she hands me notes that she had prepared ahead of our meeting to keep herself on track. At the top, she had typed: 


Why become a certified arborist? 




Read more about Honolulu’s disappearing trees in the February 2021 issue of HONOLULU, available on newsstands and in our webstore now.