When the Green Roof Garden was first planted in 2009, everything we knew about long-term rooftop gardening was theoretical. Which plants would live more than one year on the roof? No one knew for sure. Were native plants better to plant than non-natives? Unknown. What about soil depth, extreme weather, pests, diseases? The list of questions was long.
Download the results of this 5-year study. Click here.
Today, after five years of watching, waiting, documenting, and evaluating, we now have actual data to guide us—and others—on the ever-more-popular topic of green roofs! I’ve just published the Plant Evaluation Notes from our research—the first national plant evaluation study of its kind.
I was blown away by the survival rates among plants, and by the fact that so many of them thrived and even excelled in such a challenging landscape. Of the more than 40,000 plants that we installed on both roofs, 30,568 of them were still alive in 2014. Just 14% of the 216 taxa died—that’s a pretty good success rate when you consider rooftop conditions. In fact, adaptability was one of the main criteria that we evaluated each plant on. Here’s the five-point list:
Adaptability (to hot/cold, dry, windy conditions, plus shallow soils)
Pests/diseases
Winter hardiness
Non-weediness
Ornamental beauty
Other surprises? Definitely the wild white indigo (Baptisia alba var. alba). Although I didn’t expect it to fail, I also didn’t expect it to be as large and vigorous as it has become. By year five, it was nearly three feet tall, with dramatic spires of white flowers. Meadow blazing star (Liatris ligulistylis) was in the same elegant category. But the absolute standout was prairie dropseed (Sporobolus heterolepis). It looked good all year, at all soil depths, and the fragrant flowers made the roof smell like popcorn in August and September.
Antennaria dioica
Baptisia alba var. alba
Phlox subulata ‘Emerald Blue’
The Green Roof Garden today: a tapestry of plant life
It also surprised me that some of the drought-tolerant plants like sulfur flower (Eriogonum umbellatum), tufted fleabane (Erigeron caespitosa), and long-petaled lewisia (Lewisia longipetala ‘Little Plum’) didn’t do better on the green roof. Same goes for sundial lupine (Lupinus perennis). In a broader sense, I’m disappointed that we haven’t had greater success with plants in the shallowest, 4-inch soil depth. It’s the most challenging area on the green roof, so we’ll strive to add more types of plants to this trial area in the coming years.
Monitoring plants in the field
Top 10 Performers on the Green Roof
Pussytoes (Antennaria dioica)
Dwarf calamint (Calamintha nepeta ssp. nepeta)
Juniper ‘Viridis’ (Juniperus chinensis var. sargentii ‘Viridis’)
The 69 other plants that got four-star ratings (good)!
What else is coming to the Green Roof Garden?
We’ll bring in a new set of plants (both native and non-native) to be evaluated and increase the replication of trials in 4-, 6- and 8-inch soil depths. Our goal is to compile a broad list of proven plants so that anyone—businesses, architects, governmental groups, and residential homeowners—has the information they need to grow a green roof. The sky’s the limit!
Visit the Green Roof Garden at the Daniel F. and Ada L. Rice Plant Conservation Center—open ‘til 9 p.m. all summer. The garden has two halves: the Ellis Goodman Family Foundation Green Roof Garden South and the Josephine P. & John J. Louis Foundation Green Roof Garden North.
We often refer to the Chicago Botanic Garden as a “living museum.” As an art historian and a natural history museum aficionado, this term makes sense to me.
The Japanese bridge in Giverny by Claude Monet
When I worked at the Art Institute of Chicago, I helped curate the 1995 encyclopedic Claude Monet: 1840–1926 retrospective. So, when I first joined the Garden in 2006 and began thinking about the “living museum” term, I recalled that experience. Indeed, what canvas is more similar to Monet’s than our garden’s 385 acres of exquisitely arranged plants that change with the light and weather hour-to-hour—exactly like Monet’s Impressionist subjects? And then I considered the hundreds of millions of specimens in the collections of natural history museums; the only difference between these institutions’ curated collections and the Garden’s is their current state of life.
When we slow down enough to look carefully, museum collections provide us with tremendous opportunities to learn about ourselves—and the world. At botanic gardens, plants provide us with inspiration and metaphors for life; trees, flowers, grasses, shrubs, and their cycles of life reflect our own. Similarly, at an art museum, by examining closely and quietly paintings and sculptures, we open our minds to the complexity, creativity, and diversity of people who have lived and now occupy our planet. Studying the skeletons, insects and birds, ceremonial clothing, and objects from daily life in natural history museums allows us to celebrate both the magical and mundane aspects of the human spirit and to marvel at the exquisite miracle of evolution. The same can be said for the experience at a zoo or an aquarium—two other “living museum” examples. These institutions provide us a unique opportunity to admire, and also to protect through breeding and conservation programs, animals whose natural habitats are worlds away from our own.
Wyrex Edmontonia fossils
Japanese macaque
Common to all of these museum experiences is that the original “object”—whether a plant, painting, fossil, mask, fish, or monkey—is the focal point. The experience of activating all of our senses when encountering something that has been crafted by a person, by nature, or as a result of some human-nature collaboration (which is usually the case) cannot be replicated online, in print, or on the screen. Those experiences matter, too. And even though I love and admire National Geographic across all its media, I am never so moved as when I take in the paintings in a brilliantly curated art exhibition, examine the fossils or stones in a perfectly explained science exhibition, contemplate the earth and its people while examining a compelling collection of artifacts, or stop to admire the play of colors, composition, form, and chiaroscuro (the contrasts of lights and darks) of an expertly crafted garden bed.
As you can tell, I love all types of museums. However, I owe my passion for living museums, especially botanic gardens, to Lewis and Clark. Why? A couple of years before the bicentennial of the explorers’ journey, I set out on a tour of the Pacific Northwest. I was working for the Field Museum at the time. My mission was to figure out how to create an exhibition that would rival the Missouri Historical Society’s planned anniversary show, a show chock-full of all the original artifacts such as diaries and navigation devices that had been touched by Lewis and Clark’s own hands.
While I never did figure out an exhibition for the Field (since no original artifacts would be available to come to Chicago, we finally gave up since an exhibition of replicas wouldn’t do), I did stumble upon the passion that would guide the next chapter of my career.
After driving three hours through verdant, wooded, beautiful Washington State, I parked my car and started to climb the wooden staircase up a steep hill to the Lewis and Clark Interpretive Center at the mouth of the Columbia River. Along both sides of the steep path, nature was thriving. In the still-cool late-morning air, I saw and smelled—could almost taste!—moss and lichen in dozens of shades of green, gray, and yellow; ferns, mosses, and trees; and small and large butterflies. I knew at that moment that I wanted to give people, especially those from Chicago’s urban center, the opportunity to experience nature first-hand.
And that is when my journey to the Chicago Botanic Garden began, my definition of a museum expanded, and my commitment to sharing with all people the wide variety of fascinating and inspiring curated collections became life-long.
If you spot a Chicago Botanic Garden volunteer wrapping their arms around a tree trunk this summer, don’t be surprised—what looks like a loving hug is actually a scientific measurement in process.
Using a specially designed tape measure, volunteers are recording the diameter of each tree before calculating the amount of carbon dioxide it stores. The study, launched by the Living Plant Documentation department five years ago, records the amount of the pervasive greenhouse gas stored by the Garden’s trees. The research team is interested in determining which trees are able to hold the most carbon for the longest amount of time.
Boyce Tankersley and volunteers measure the diameter of each tree on the Garden campus.
The Tall and Short of It
It is one of the first such studies underway in a botanic garden setting. “We know carbon is increasing but we don’t have the numbers on how much carbon is being locked up by the urban forest,” said Boyce Tankersley, director of the Living Plant Documentation department. “This is where the Garden can play a role.”
Although similar studies have been completed by the lumber industry and others, it is important to understand how increased levels of carbon dioxide in the atmosphere are mitigated by cultivated trees, explained Tankersley. It’s also essential to document how those trees fare long term in evolving conditions.
The Garden has an especially diverse number of taxa, Tankersley said, positioning it perfectly to document how numerous species behave in locations from the McDonald Woods to the English Walled Garden to the parking lot. “The Garden is among the first to look at the trees in a Garden setting and at the diversity of taxa,” said Tankersley. “That’s a piece we’d like to shed more light on.”
This summer marks the second time the trees have been measured since the original data was gathered in the first year. Measurements will continue to be taken for another 15 to 20 years.
“We hope, when the data is analyzed, to be able to identify not only the trees that are best but the Garden settings that support their efforts in this regard,” anticipated Tankersley.
The Living Plant Documentation department is calculating the amount of carbon dioxide stored in each of the Garden’s trees.
Deep in the Woods
Trees are lauded for coming to our rescue in the face of climate change, but scientists have learned that these strapping heroes may not be infallible. “One thing we are looking for is the influence of carbon on the growth rate,” said Tankersley. His research team is paying close attention to the trees’ response to increased carbon levels in our atmosphere.
According to Tankersley, it has been documented that trees are growing more quickly than they have in the past, which comes with positive and negative repercussions. “Trees are providing an environmental service in a major way by absorbing carbon, but there’s a point of diminishing returns,” he explained. The wood of a fast-growing tree is softer, for example, which has a negative impact on the lumber industry, he explained. In addition, “with an increased growth rate, you also get increased susceptibility to insects and diseases.”
The concern underscores the need to observe the Garden’s trees for many years to take all such factors into consideration.
In addition, the team is watching the impact of weather on the trees, and taking dry spells or rainy periods, for example, into account when documenting tree growth over a given time frame. The Garden hosts a National Weather Service monitor on-site, which allows for weather-related calculations to be even more precise.
The Zipline
When the measurement phase of the study is complete, Tankersley plans to provide the data to a doctoral student in the Garden’s joint degree program with Northwestern University for formal analysis. “My take-home would be a list of the six best trees, perennials, and shrubs for sequestering carbon in the landscape in Chicago,” he said.
“We expect to find that trees like oaks, elms, and hickories—trees that are long-lived—provide a greater environmental service in this regard,” he added.
For homeowners who would like to assist with the issue now rather than wait for the final analysis, he suggests that they begin planting longer-lived trees. It may help mitigate, or reduce, the amount of carbon in the air and resulting climate change impacts such as extreme weather.
It takes more than one year for the Garden volunteers to check the diameter of the 13,493 trees on-site, and enter the estimated carbon storage into a specialized database. The calculations are made using a formula developed by the U.S. Forest Service, said Tankersley.
The technique of measuring existing trees and planning for new plantings is something Tankersley hopes will have broad impact. He has already shared his process with countries in Africa through The Eden Projects and in China in an effort to help governments replace denuded forests there.
Tankersley is hopeful about the long-term implications of the study. After all, he said, when pioneers first came to the United States, they found oak trees that were about 300 years old, and had been providing benefits such as carbon sequestration for all of that time. Many of those hard-working, long-lived species have been a key part of our natural heritage since the beginning. By embracing the issue now, Tankersley and team have cleared the way for trees and their vital functions to endure.
The Garden received recognition and praise for two outreach programs at the recent American Public Gardens Association (APGA) Conference.
Award for Program Excellence
The American Public Gardens Association awarded the Chicago Botanic Garden’s Science Career Continuum the national Award for Program Excellence, marking the third time the Garden has received this prestigious prize since it was established in 1989.
“a truly innovative spirit in the development of an original program with demonstrated results”
This honor recognizes an APGA member garden that has innovated in conservation, botany, research, or other public garden areas of expertise. The Garden won the award for its groundbreaking Science Career Continuum. On June 23, during its annual conference, the APGA review committee praised the Garden’s program, saying “The Science Career Continuum has displayed a truly innovative spirit in the development of an original program with demonstrated results. APGA is proud to have programs such as yours at its member gardens.”
The Garden’s recently retired vice president of community education programs, Patsy Benveniste, and CEO Sophia Shaw receive the Award for Program Excellence from Casey Sclar, Ph.D., executive director of APGA.
The Science Career Continuum engages 65 Black and Latino youth from Chicago Public Schools in science through hands-on exploration of nature, mentored internships, and college and career preparation with the aim of increasing the representation of people of color in environmental science careers. Over the past five years, these students have shown a 100 percent high-school graduation rate, 92 percent college matriculation rate, and 76 percent selection of science, technology, engineering, or math (STEM) majors, 65 percent of them in science.
“the Chicago Botanic Garden has, for more than 30 years, used its unique resources to provide opportunities for healing…”
Ford Bell, the recently retired president and CEO of the American Association of Museums in Washington, D.C., also praised the Garden in his keynote presentation.
Bell said, “Museums of all types are, at their core, community institutions, and I like to say, if you name a community problem, I will find you a museum somewhere in our country that is working to address that problem. I was certainly reminded of that at AAM’s Advocacy Day in February, when Iraq War veteran Fernando Valles was honored as one of our Great American Museum Advocates at the closing evening reception. Fernando was nominated for the award by the Chicago Botanic Garden, where he is a participant in the Garden’s initiative for veterans suffering from post-traumatic stress disorder and other emotional challenges, in partnership with Thresholds, a community-based mental health agency. It is certainly admirable that the Chicago Botanic Garden has, for more than 30 years, used its unique resources to provide opportunities for healing, stress reduction, physical exercise, and learning through its Horticultural Therapy Services, a striking example of the work that museums and gardens do in their communities, work that is often unheralded.”
Wildfire. Flooding. Thirst. These issues can all be addressed through large-scale landscape restoration, according to speakers at the 2015 Janet Meakin Poor Research Symposium. Addressing a crowd of regional stewardship professionals and academics, as well as Conservation Land Management (CLM) and Research Experiences for Undergraduate (REU) interns at the Chicago Botanic Garden on June 12, they focused on solutions for ecological challenges.
The effects of strong conservation work are magnified when done on a large scale, they shared, and the theme of the day was how to magnify every step from seed-management procedures to restoration time frames and budgets to make the process as beneficial as possible. As mining, drilling, and similar industries move broadly across open lands in the United States and abroad, along with increasingly frequent and far-reaching extreme weather events, conservation practices must evolve with the times to keep pace.
Conservation and Land Management (CLM) interns measure species density in the field.
As the CLM interns prepare to set off on a summer of hands-on restoration work across the United States, and potentially launch their careers shortly thereafter, these are critical issues for them to understand, according to Kay Havens, Ph.D., of the Chicago Botanic Garden, who organized the symposium. Many of the interns work in partnership with the Bureau of Land Management (BLM) on the ground in forestry, wildlife management, and habitat restoration, among others.
Fittingly, the first speaker of the day was Amy Leuders, the acting assistant director of BLM, who noted that the partnership with the Garden since 2001 has led to the training, hiring, and placement of more than 1,000 interns on federal lands. About 50 percent of those interns are later hired by a stewardship agency. “The Bureau of Land Management has had a long and successful partnership with the Chicago Botanic Garden…developing the next generation of land stewards,” she said.
In particular, she imparted to the audience the importance of developing a large scale national seed strategy, so that targeted plant seeds will be thoughtfully collected and preserved for future use. She cited examples of events in which seeds saved by chance allowed for the restoration of areas that later succumbed to natural disasters like wildfires and hurricanes. This new process would allow for seed saving to take place in a more proactive and calculated manner.
According to the second speaker, Kingsley Dixon, Ph.D., professor at Curtin University and the University of Western Australia, the current supply of wild seed cannot support global restoration demands. Innovations are helping to change that. Tools that process seeds into pellets or other small packets facilitate their successful mass delivery into recovering ecosystems, helping to achieve the level of seed performance seen in the agricultural sector. He noted that “Only by thinking at an industrial level of efficiency will ecological restoration be able to achieve the pace needed to protect and enhance natural resources.”
Drinking water quality can also be managed by restoration, said Joy Zedler of the University of Wisconsin-Madison. She shared examples of how restoration has been “scaled up” adaptively (learning while restoring) to benefit large areas. When it comes to managing water, she explained, it is essential to manage an entire watershed. One area of poor water quality will flow into every crevice in the system, for example. In the end, she explained, it is about safeguarding ecosystem services that human health and wellbeing depend on, from clean water to fresh air. “Our global society needs to redirect itself to achieve a sustainable future,” she said.
Brian Winter of the Nature Conservancy in Minnesota echoed her sentiments, as he ran through a real-life wetland restoration process for the audience. He emphasized that wetlands hold rainwater and are capable of preventing disastrous amounts of water from washing through nearby agricultural fields. The value of wetland restoration is immense and ongoing, he explained.
Conservation is in transition, explained speaker John Rogner of the U.S. Fish and Wildlife Service. Rogner discussed the steps involved in planning for a successful restoration, and the importance of landscape conservation cooperatives that can work together across states or even countries to identify and address issues in a given geographic area such as the Great Lakes watershed. He outlined an ongoing project to improve blockages in the Great Lakes system that impede fish migration. This can lead to a buildup of invasive plant species that create additional system blockages. A regional perspective and collaboration across entities is critical, he said. “It is absolutely essential that everyone have access to the same information to keep moving in the right direction,” added Rogner.
Issues that often fall to the side in planning are conceptual, according to James Aronson of the Missouri Botanical Garden. He urged the audience to pay attention to the economic side of their work by learning to speak and think in terms of renewable natural capital. Across land and ocean, natural capital can be restored to facilitate the flow of ecosystem services such as fresh air and clean water.
One of our greatest national resources and treasures: the Colorado River Basin.
Lastly, Megan Haidet with Seeds of Success emphasized the importance of partnerships to meet the goals of the Bureau of Land Management’s National Seed Strategy for Rehabilitation and Restoration 2015–2020. She noted that increased coordination is vital to accelerate the pace and scale of restoration and provide native plant materials when and where they are needed.
The Garden’s CLM interns have now dispersed across the United States, where they will work for the next five months on public lands to put these lessons into action.
