Chicago’s most famous rooftop garden sits atop City Hall

My first Monarch of the season was spotted on the roof of City Hall in Chicago.

That’s right – a prairie on top of a roof surrounded by a jungle of tall buildings and concrete. We were there courtesy of the Rock River chapter of Wild Ones, a not-for-profit environmental education and advocacy organization.


Our guide Kevin Carroll explained that Mayer Daley first saw rooftop gardens in Hamburg, Germany during a visit in 1998. City Hall needed a new roof and a settlement from ComEd provided the funding. The garden was first constructed in 2000 then turned over to Chicago Department of Transportation in 2003.


We entered the rooftop through what I can only describe as “the boiler room”.


What is unique about the City Hall garden is the use of native plants. While most of the “green roofs” in Europe are comprised of low growing Sedums and similar drought tolerant plants, City Hall’s roof is planted with Midwestern natives, plants well noted for their ability to form deep tap roots that allow them to survive our harsh climate.

But . . . on a rooftop? On shallow soil?

Eryngium yuccifolium

As new manager in 2003, Carroll put in a new irrigation system, killed weeds, reseeded bare areas and introduced a wider variety of prairie natives.

Kevin Carroll

The ability of the prairie species to thrive in the shallow soil – 1-1/2” to 6” deep – has been most astonishing.

They did not know what to expect.

Physostegia virginiana

Many towered over our heads – just as they do in the prairie.


By 2010 there were 220 species of plants in the garden. More than 100 species of birds have been observed on the roof during spring and fall migration, so exhausted by their flight they do not exhibit fear or fly away when approached.

So . . .

where would they go?


“It’s really the Rolls-Royce of green roofs.” said Michael Berkshire who administers green projects for the city. Some areas of the roof have rolling terrain with an added 18-inch layer of soil to support one Prairie Crabapple and a mass of Junipers — welcome protection for the birds clustered by the dozens in their branches.

Malus ioensis

The garden absorbs less heat from the sun than the old tar roof, keeping City Hall cooler in summer and requiring less energy for air conditioning. Chicago estimates that this green roof saves City Hall about $3,600 a year in heating and cooling savings.

The juxtaposition of prairie with urban was most startling, especially considering we were 12 stories off the ground.

I could happily wander around up there for hours!


Kevin guided us through the garden as we recognized the prairie plants that we
were familiar with, along with a few that we were not.

Allium cernuum

Lobelia cardinalis

We were cautioned about getting too close to the edge.

It’s a

L O N G W A Y D O W N !

A long way down

The eastern half of the building belongs to the County with the typical roof of black tar. On a hot day, the surface temperature measured nearly 80 degrees hotter on
the black side (tar) than the green side (prairie).

Restricted Area

Chris maintains the garden daily, removing weeds – mostly black medic, yellow nut sedge and sweet clover – and deadheading plants that might be excessive seeders.

He sometimes forgets to take lunch.


Kevin and Chris pointed out plants that have done exceptionally well (Prairie Dock, Penstemons, Lead Plant, Verbena, Purple Prairie Clover along with the grasses like Big Bluestem) and showed us the noticeable effect that nitrogen-fixing legumes like Amorpha and Baptisia had on their neighbors.

I snatched this picture from the web to show you Baptisia in bloom.


The garden is not open to the public but can be seen from surrounding buildings and by appointment. Visitors from all over the world have come to see it.

Thank you, Jim, for putting up with my forays into the “wilds”. You are a good sport.

Eventually we took the elevator down to the “reality” of big city life meandering over to Millenium Park.


And another rooftop garden . . . of sorts.

Michigan Avenue


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