Pop quiz: What kind of natural habitat is increasing in urban areas? This is not a trick question. Rather, the answer offers a slice of good news on a planet that has been increasingly turning from green to gray.
Kelly Ksiazek-Mikenas, Ph.D., in the Plant Science Lab
Dr. Ksiazek-Mikenas, a former biology teacher, spent six years studying these engineered habitats and their potential to support biodiversity.
The plant scientist is now eager to share her findings: When started carefully and with a long-term plan in mind, these sites do grow up to support species, natural communities, and genetic diversity.
“When you have these three pieces working, you have a good foundation that should sustain plant life over long periods of time and live through environmental changes, and that look and function like a diverse prairie,” she said.
Dr. Ksiazek-Mikenas examined shallow (up to six inches of soil depth), low-moisture roofs from Glencoe, Illinois, to Neubrandenburg, Germany, before reaching that conclusion. While the roofs within the United States are generally younger, some in her German sites were up to 93 years old, providing a mix of data about green roofs at all ages. She also studied data sets and conducted shorter-term experiments to clarify the qualities green roofs need to succeed.
Dr. Ksiazek-Mikenas sets up insect traps in 2013 on a green roof in downtown Berlin.
Her work had its ups and downs. She arrived in Germany looking for similarities, expecting the insect and plant species on one roof to mirror that on the others. Rather, she found differences between roof gardens. After a deep dive into data, she found the secret. Although the plant species differed between gardens, those that grew well shared the traits of being stress-tolerant and adept at establishing themselves in new areas.
She was concerned by the lack of diversity on individual roof gardens both in Germany and in her study sites in Chicago.
Back at the Chicago Botanic Garden, she set up an experiment to test how different soil types would affect which plants were successful, and whether she could create a more diverse community on one rooftop by planting both rock and sand prairies.
She planted her experimental plots on the Josephine P. & John J. Louis Foundation Green Roof Garden North on the Daniel F. and Ada L. Rice Plant Conservation Science Center and monitored activity over three years. She found success in growing a more diverse habitat. In related work at the same site, she confirmed that native plantings, rather than the common sedum plant mix used on roof tops, offered benefits similar to a native prairie when it comes to storing rainwater, for example.
The Plant Science Center’s Green Roof Garden is an important resource. Planted in 2009, it serves as a living laboratory, classroom, research site, and a source of inspiration to visitors.
A blooming population of Penstemon hirsutus was part of Dr. Ksiazek-Mikenas’ experiments.
She then expanded to include plots on the Ellis Goodman Family Foundation Green Roof Garden South to study genetic diversity. She compared the genetic diversity of populations established from nursery stock to natural populations, finding more diversity in the natural populations grown from wild collected seed.
On the heels of that finding, she studied populations on green roofs in Chicago near Lake Michigan to find out if the plants were able to share their genetic material with plants on neighboring roofs through pollination. She was thrilled to confirm that they did, as the exchange of diverse genetic material is essential for the long-term health of a species.
Although there are limitations to green roof gardens, mainly due to the lack of soil depth and disconnected setting, Dr. Ksiazek-Mikenas is optimistic about their ability to sustain native species. She has presented her work at numerous conferences across the globe to academics and those in the landscaping industry.
Two prairie species in Dr. Ksiazek-Mikenas’ experimental plots—Ratibida pinnata (foreground, right) and Lespedeza capitata (background, left)—bloom on a green roof on the Peggy Notebaert Nature Museum in Chicago.
“In the future, I hope that green roofs can continue to provide ecosystem services to people but also increasingly support a wide variety of urban biodiversity,” she said.
The motivated researcher is ready to move ahead with her career and intends to continue to bring her unique perspective to future students and to the development of more green infrastructure in this growing world.
Gardeners and farmers know that healthy plants need good soil and the right amounts of both water and sunlight. But green roofs are intentionally built with an engineered soil-like substance that more closely resembles a pile of rocks than rich, moist potting soil.
To make matters worse, the tops of buildings are often blindingly sunny and very hot in the summer. So how do plants like grasses and wildflowers survive in this type of harsh environment?
Cactus and other succulents retain water in their tissues. Ornamental onion (Allium) species have underground bulbs that help them get through cold winters and dry summers.
Not all plants will grow on a green roof, even in the temperate Midwest. Most plant species that are successful in the desert-like habitats of green roofs have beneficial adaptations that allow them to absorb and store water and nutrients. Some have succulent leaves with thick waxy coatings to prevent water from evaporating. Others have roots that grow horizontally rather than vertically to maximize the areas from which they absorb water and nutrients. Some use a modified type of photosynthesis to prevent water loss during the hottest and driest part of the day. Still others use bulbs or underground tubers to store nutrients during the long cold winters. Some species may even form partnerships with special fungi in the soil that help their roots with more effective absorption.
While plant species evolved to develop these various adaptations on the ground, such traits serve the individual plants very well in the harsh environment of a green roof. The next time you visit a green roof, you might see a striking diversity of species but you won’t see any wimps. No, these plants are both beautiful and tough.
Even in very shallow soil and full sun, some plants that normally grow in shortgrass prairies are able to grow and reproduce. (This is from some of my research at Loyola University.)
Plants can be both tough and beautiful on green roofs. (This photo is of the Plant Science Center last summer.)
Find more of the best plants for green roofs on our Pinterest board, and see Richard Hawke’s Plant Evaluation Notes for the plants that performed best on our green roof.
Students in the Chicago Botanic Garden and Northwestern University Program in Plant Biology and Conservation were given a challenge: Write a short, clear explanation of a scientific concept that can be easily understood by non-scientists. This post is part of their series.
We’ve selected the top 9 plants for green roof gardens from our 5-year study of 216 taxa. Download the results of plant evaluation manager Richard Hawke’s extensive study.
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.
Do you ever feel like trying to understand plant science research can be as daunting as deciphering a passage written in a foreign language?
As a budding plant scientist in the joint Chicago Botanic Garden/Northwestern University Ph.D. program, I find it exciting to pick through dense scientific text. Uncovering the meaning of a new acronym and learning new vocabulary can be thrilling, especially when decoding something new.
This past fall I spoke to a group of green infrastructure professionals in Sydney about the importance of urban biodiversity.
But the commonly used styles in scientific writing and presentation packed with language used to convey big topics in small spaces can be really off-putting to an audience of non-scientists. Many of us can conjure up a memory of a professor or teacher who seemed to like their subject matter but couldn’t convey the material in an interesting way. All of a sudden, science became boring.
Rather than struggling to learn this “foreign language,” many folks stop paying attention. Lack of scientific literacy, especially as it applies to plants, is a pity. Plants are all around us! They are so valuable to the entire planet. The very applicable field of botany shouldn’t be something that’s only discussed and understood in laboratories or scientific conferences—it should be for everyone.
This idea inspires me to try and bring my current botany research to a wide variety of people.
I’ve had the chance to speak with many visitors to the Chicago Botanic Garden about my research, and typically bring some of my research supplies, as seen here from a trip to Pittsburgh.Writing and publishing a children’s book helps bring my research findings to kids all over the world.
For example, I recently realized that there are very few resources available to teach young students about the habitat where I currently collect most of my data: green roofs. While some of the methods I use for data collection and analysis can be quite complex, the motivations behind my work and some of the findings can be broken down into some basic ideas, applicable to students of all ages. So a fellow botanist and I wrote and produced Growing Up in the City: A Book About Green Roofs.
Our children’s activity book teaches youngsters about some of our research findings. The book follows a pair of native bumblebees through a city, where they guide the reader through engaging activities about the structure, environmental benefits, and motivations for building green roofs. At the end, readers even have the opportunity to ask their own research question and carry out a green roof research project of their own.
Interested in your own copy of our book? More information and a free digital download of the book are available at greeningupthecity.com.
Talking to 100-plus middle school girls about why it’s cool to be a botanist was a great experience!
The activity book is just one example of ways that plant scientists can engage with a broader audience and make their research findings more accessible. Some of the other activities that my colleagues here at the Chicago Botanic Garden and I have participated in include mentoring undergraduate and high school students, speaking to community organizations, creating lessons for schools and school groups, volunteering for summer programs, and maintaining a presence on the Internet through online mentoring, blogging, websites, and Twitter.
Teaching undergraduate students how to identify plants on green roofs is one way of passing on my research knowledge.My experiments on the green roof at the Plant Science Center are visible to everyone. Come take a look!
Here at the Garden, we scientists also have a unique variety of opportunities to share our science with the thousands of visitors who come to the beautiful Daniel F. and Ada L. Rice Plant Conservation Science Center. If you’ve never been to the Plant Science Center, you should definitely stop by the next time you’re at the Garden. You can see inside the laboratories where the other scientists and I collect some of our data. There are also a lot of interactive displays that aim to demystify plant science research and decode some of the “foreign language” that science speak can be. For a really interactive experience, come visit us on World Environment Day, Saturday, June 6, and talk to scientists directly. Bring your kids, bring your neighbors, and ask a botanist all those burning plant questions you have! We promise to only speak as much “science” as you want.
