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Chicago Botanic Garden - Prairies and Green Roofs

Chicago Botanic Garden is huge - 385 acres with 27 garden areas and ‘four natural areas’ and is interesting in that it is a chain of nine islands set in a forest preserve. It is immaculately kept, whilst I was there they had a Roberto Burle Marx inspired annual display, and unfortunately they had experienced some flooding and damage in the garden. Environmental issues like these is becoming more and more a common situation that many gardens have to face, and it is always interesting to see how gardens deal with it. It was clear where the damage was, a drift of Cotoneaster shrubs were rendered dead and the bottom of a row of box hedge had a dusty appearance and was a different colour to the rest of the bush. The best thing was that the garden instead of trying to hide the damage or being really apologetic about it, used it as an educational opportunity with simple signs informing the public of what had happened, and making them aware of the problems that can arise in changing climates.

Chicago Botanic Garden's Waterfall Garden with pool and water plants surrounded by trees and a neatly striped lawn in the background
Photo 1: Chicago Botanic Garden's Waterfall Garden with perfectly striped lawns in the distance.


My favourite area there was the Native Plant Garden inspired by their native plant palette of flora of which designers Oehme van Sweden had a hand in (they have created a great area of similar ilk at New York Botanical Gardens also).

Chicago Botanic Garden's Native Plant Garden - a white combination of Cleome spinosa 'Helen Campbell' and Hibiscus moscheutos
Photo 2: In the Native Plant Garden - a combination of annual Cleome spinosa ‘Helen Campbell’ and Hibiscus moscheutos - the hardy swamp rose-mallow that grows in wetlands in Eastern USA.



Chicago Botanic Garden's Native Plant Garden with plantings of predominantly pink Echinacea, Perovskia atriplicifolia Blue Spires and Eutrochium
Photo 3: Native Plant Garden - very similar to plantings found in the UK inspired by North American prairies created by people like Oudolf and Hitchmough

I was fascinated by the man made mounds of Dixon Prairie, because I have been to see a few prairie environments now and was intrigued that there was such a concentration of the juicy stuff - Euphorbia corollata and Silene virginica, which I had seen in scarcer quantities elsewhere, and I felt that it could have been to do with it being better drainage on slopes.

Chicago Botanic Garden's Dixon Prairie with dense masses of Euphorbia corollata
Photo 4: Dixon Prairie - a dense amount of Euphorbia corollata

Chicago Botanic Garden's Dixon Prairie with vivid red Silene virginica and Euphorbia corollata
Photo 5: Vivid Silene virginica

Then it was amazing to see their green roof experiments after this on their Daniel F. and Ada L. Rice Plant Conservation Science Center and find a correlation between them that I would not have made a connection before. The roof garden is 16,000 sq ft and there were two distinct areas to them - on one side were grown the plants that were known to be good for green roofs, there was a strong tapestry of low lying sedums, and on the other side were native plants of rock and prairie habitats. Both areas were also split into different sections of soil depth (four, six and eight inches deep), and looked at how the same plants performed in each depth.

Green roof at Chicago Botanic Garden with plants known as good for green roofs plus potential one. A tapestry of sedums in the middle
Photo 6: Green roof on the Daniel F. and Ada L. Rice Plant Conservation Science Center at the Chicago Botanic Garden with plants that are known as good green roof plants plus potential ones.

Photo 7: Green roof using native prairie plants not usually used for green roofs

It was the native green roof area that really surprised me - I instantly was taken in by the relaxed feel of it and how successful the colonisation of it was - in the deeper soil areas vegetation was definitely thicker, but in shallower areas - certain kinds of plants were able to thrive better that were more drowned out in the bushier growth. Free draining definitely makes sense in a wildflower context - part of the less nutrients in the ground the better for diversity, this and the success of the standing out of certain flowers on the Dixon Prairie mounds seemed to confirm this.

I have a slight paranoia about green roofs although I know some good work is being done and has been done on them, only because I have witnessed them being taken up as a fad and done really badly, so all you see is awful scorched brown weeds throughout most of the year. The idea of them is great, but often the execution fails. Nevertheless there is no doubt that they are a good thing. In the States because the country gets more extreme weather, they have been more conscious about making grey urban areas more environmentally accommodating and green roofs can be an integral part of that. In fact a lot of cities have compulsory rain gardens and storm water management and strategies - definitely something the UK can take a leaf out of more. Successful green roofs can fill in the biodiversity gap as we lose more nature to concrete, they can help with water run off and keep a building cool. People like Nigel Dunnett are really pushing for features like these in contemporary landscape architecture, as he was a former GCA/ RHS Fellow (formerly known as the McLaren Trust) I can’t help but think he might have had some influences from the States. Prairies are a salient point in the Midwest; long has prairies in North America been most under threat - only 1% of original prairie land remains in Illinois, long have they been seen as stretches of monotonous grasslands to dominate - a gross oversight to the actual diverse biomes that they are, so using native plants in green roofs can compensate a little for the prairies that have been lost or at least encourage some sort of diversity to what would have been lifeless.

I asked Richard G. Hawke - Plant Evaluation Manager Associate Scientist who was showing me their trials area and the green roof, why if native prairie plants seem to colonise green roofs so well and looks good, that this palette wasn’t more widely used. He replied because of the worry of them catching on fire. This was a fair point, but I optimistically wondered about whether there were ways around it as it seems like such a good opportunity.

There is great information about their work on the Chicago Botanic Garden website - including about the scientific research they have been doing on the green roofs - http://my.chicagobotanic.org/tag/green-roof/


When I was doing the GCA/ RHS Interchange Fellowship in the USA 2016-17, there were things I did not manage to cover in my report about my experience there. One of those was a trip to Chicago in August 2017, so I am posting all of these extras onto this blog. GCA member and my main point of contact Celine Lillie lives there and kindly invited me to visit. Additionally Andrew Bell who was doing the Longwood Fellow’s programme at the time, had lived there also and had worked at the Chicago Botanic Garden - he amazingly hooked me up with lots of contacts he knew there, including Jacob Burns - Curator of Herbaceous Perennial Plants at CBG who also generously hosted me. To all these people I am most grateful.

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