Potential green roof plants

[GreenRoofer]

I am hoping to draw on the experience of Rock gardeners for potential new plant materials for green roofs. Plants that would work well, would include, those that like it hot, dry, sunny, windy, and exposed, in a gravelly somewhat alkaline shallow soil with around ~20% organic matter, and ~80% mineral. Currently, sedums dominate the market. Other plants in somewhat common use include those of the genera; Allium, Talinum, Opuntia, and Sempervivum.

I'm thinking there's many more out there, that would love a green roof. Any ideas?

I'm also planting alpine plants in 6" of green roof media in planters on my windowsills at home. I'm not sure how they'll deal with the reflections off the windows. I'm sure some won't like Chicago, some will succeed.

My current windowsill is planted with;
Acantholimon armenum
Androsace hirtella
Anemone blanda 'enem'
Arabis x kellereri
Astragalus angustifolius
Calceolaria ex. garden Barrie Porteous
Campanula betulifolia
Campanula trogerae x betufoliae
Daphne 'Lawrence Crocker'
Daphe 'Schlyteri'
Draba bryoides
Penstemon uintahensis
Penstemon virens
Petrophyton hendersonii
Saxifraga 'Sieberi'
Silene acaulis 'Anne Spiegel'

Currently these are all dormant, but have Southern exposure. I can change to an Eastern exposure without too much difficulty. Does anyone have any thoughts?

[cohan]

Hi and welcome! You'll find that alpine/rock garden sources have some of the most diverse offerings of any type of gardening, so you have a lot to choose from.
I'm sure some here will have specific recommendations but you can also find a lot just looking through seedlists such as Alplains and other suppliers such as Highcountry Gardens and many other alpine nurseries. Keys for your purposes, I think, will be looking at the habitat of plants- you don't want those from cool alpine tundra, moist alpine valleys or snowmelt areas- all places where plants may expect constant moisture.
At a guess you might look at plants from places like  alpine Turkey and western U.S. alpine/dryland areas that experience dry conditions..
Hope you'll keep us posted of things you try and future projects!

[GreenRoofer]

I certainly will, here's a picture of my plant order from Wrightman Alpines. I've also sewn alpine seed from 'plant world seeds' outdoors in similar windowsill planters. These are my initial trial plants for Chicago.

[Tim Ingram]

Excellent environment for alpines! I grow quite a few on your list on a sand bed; a lot deeper than 6" but otherwise probably similar in many respects. Have you seen the book 'Planting Green Roofs and Living Walls' by Nigel Dunnett and Noel Kingsbury? This has extensive listings of many alpines and small perennials. The authors are both extremely knowledgeable and the information from good experience.

[Hoy]

These plants are growing in pure sand, in eastern Turkey: Artemisia sp, Orobanche sp, Astragalus sp, Campanula aucherii, Gypsophila?

[Weiser]

Here are a few general suggestions, of genera to look at. Many have low mat forming species that may thrive on shallow soils and dry breezy exposures of the roof tops. As was suggested look at the western dry land species.
Eriogonum
Erigeron
Arenaria
Minuartia
Phlox
Antennaria
Townsendia
Epilobium
Camissonia
Calylophus
Oenothera
Potentilla 
Penstemon

[GreenRoofer]

Dunnett is my homeboy. Havent read that one, but own a few of his other books and quoted his research heavily in my thesis. Snodgrass has a book on green roof plants that's pretty great. I always feel however, that until you grow a plant yourself, you don't really understand it. I've been putting together a large body of research on potential green roof plants, and I'm currently trialing 86 species on a semi-intensive green roof system. But alas, it is winter, and not much is happening with them. So I read, and prepare for my window of opportunity. The research roof is going into it's third season, and as they say, "sleep, creep, leap". So this season will really be awesome I hope.

Regarding western desert species, I have added seed from Erysimum capitatum. I hope it likes the environment.

[Tim Ingram]

It would be worth contacting Nigel Dunnett directly (at Sheffield University). I think he would excited to hear from anyone trialling plants in this way and he is very approachable.

[McDonough]

Hello JD, a belated (from me) welcome to the NARGS Forum, been working overtime this week. Green roofs is a most interesting topic, one that I'm personally fascinated with. I believe all of us here would like very much to learn more about your work with green roofs, and help brainstorm on plants most appropriate for such conditions.

Years ago when I was a young boy, my family would frequently vacation in Montreal, and stay at the Bonaventure Hotel (now Hilton Montreal Bonaventure), a wonderful and distinctive hotel.  The hotel itself is the top 3 floors of a huge conference center, the top 2 floors also look inwards towards 2.5 acres of mature landscape, pools, and a maze of running streams and waterfalls, all at rooftop level.  The landscaping was stunning, one of the first green-roofs, way ahead of its time.  Even the drive-up entry plaza is a green roof over the parking garage.  The integrated landscape/waterscape features were designed by large multidisciplinary Boston area design firm Sasaki Associates, perhaps best known for large scale Landscape Architecture projects. I did not know this fact until much later in my life.

Hilton Montreal Bonaventure hotel - rooftop gardens and water features
http://www3.hilton.com/en/hotels/quebec/hilton-montreal-bonaventure-YULBHHF/index.html

http://www3.hilton.com/resources/media/hi/YULBHHF/en_US/img/shared/full_page_image_gallery/main/hf_exterior2_2_675x359_FitToBoxSmallDimension_Center.jpg

Google images:
https://www.google.com/search?hl=en&q=bonaventure+hotel+montreal+gardens&bav=on.2,or.r_gc.r_pw.r_cp.r_qf.&bvm=bv.41524429,d.dmQ&biw=1268&bih=818&um=1&ie=UTF-8&tbm=isch&source=og&sa=N&tab=wi&ei=hK8BUYjSO-e20AG9uYGADQ

After choosing a career in Architecture, I ended up working for Sasaki Associates, it was a pleasing coincidence to discover it was this firm that designed the amazing gardens at the Bonaventure Hotel.  I worked for this company a total of 20 years (worked for them twice); I find their work in all disciplines (Architecture, Landscape Architecture, Interior Architecture, Civil Engineering, Urban Planning) to be of the highest quality and inspiring.  They do quite a bit with green roofs, here are some links.

ASLA - LAND online, landscape architecture news digest, August 2006
Sasaki Associates: A Comprehensive View on Sustainable Design
Photo example of the Manulife building in Boston, with a beautiful prairie-grass style green roof planting.
http://landarchives.asla.org/2006/0807/sasaki.html
...another article on same building
http://www.landscapeonline.com/research/article/6965

ASLA green roof articles
http://www.asla.org/ContentDetail.aspx?id=25382

Sasaki Associates project: The Avenue, Washington DC, the detail section views are really interesting.
http://www.sasaki.com/project/8/the-avenue/

Sasaki Associates, selected portfolio images of Green Rood designs.
http://www.sasaki.com/projects/tag/green+roof/

[RickR]

Ed Snodgrass was the speaker at our Chapter banquet in 2008.  We all learned a lot.

You might also consider some of the miniature bearded iris.  Some Chapter members here have a green roof on their shed.  They resolved to grow no sedum or sempervivum spp. there.  At the moment, the only things I can be sure of that they do have up there are dianthus spp.  They do say that grasses (no specification) are unwanted weedy volunteers.  I might be a little leery about introducing grasses intentionally, but perhaps Bouteloua hirsuta.  B. gracilis, I think, would be too vigorous.

[GreenRoofer]

That really is wonderful, from Sasaki. That's some roof, it's rare that a space like that is created and then maintained properly for years and years.

Regarding grasses on green roofs, they are wonderful.

To explain my theory on green roof ecology, I start with a successional model. I believe that a green roof installed with Sedum is the first step along a greater journey. Initially plants like lichens and mosses colonize rocks and create primitive soils which hold more moisture. Then larger plants move in, establish a grassland, then a forest. In the case of a green roof, abiotic factors like wind, temperature, media depth, fertility, and sunlight limit which stage of succession the green roof is 'frozen' in. I argue that Sedums are analogous to mosses and lichens in green roof succession. A lot of people villify Sedums, even on here. I view them as the dominant organism on an extensive green roof (4"), and as a colonizer on a semi-intensive system (6"). Once they create a thick rhizosphere, then other things can become successful, like grasses and forbs. I use Sedums to create 'islands' of moisture and life, then I introduce grasses and forbs into these islands. I'm a huge advocate of using seed on green roofs. Alpine gardeners seem to believe in utilizing seed as well. Everyone in my industry is so damn impatient. I view a green roof as a three year establishment. Many believe that simple maintenance on a green roof, something as simple as irrigating twice a month in the growing season, is just too much to ask. I disagree.

Attached is one of the roofs I maintain. I think the grasses are beautiful. If I were to recommends any, I'd say Eragrostis spectabilis and Koeleria macrantha are my favorites. They're both rather short at under 2 ft, at least for a prairie grass. I'm trialing Danthonia spicata, and I'm very optimistic that it will do great.

Regarding Dianthus on a green roof, it can be done in a wetter climate or on a maintained green roof. Otherwise, their dependence on their tap root in a shallow media can make them decline over a period of years. I can't however say how they would do in a semi-intensive media depth. They might do very well. I'm trialing D. 'Firewitch', so let's hope. greenrooftechnology.com suggests D. carthusianorum.

I would like for NARGS as a whole to view Sedums more favorably, I know they're 'too easy', but they can act as a placeholder for more slow to establish species. And in flower, they can be stunning as a mass.

[GreenRoofer]

I think I'll contact Dunnett in the Spring, I want some good pictures of the trial roof in bloom.

[Harold Peachey]

Our local native plant guru, Dr. Leopold of SUNY ESF  is researching native plant material for greenroof application.  He has taken a bit of different approach.  The link will take you to some information and scrolling down is an interesting list of plants he is experimenting with.
http://www.esf.edu/outreach/gi/symposium/documents/toland_etal.pdf

(Moderator note: to gauge download time, PDF file size is 7.7 MB)

[GreenRoofer]

Thank you, Harold, that's pretty cool. It's so hard to source plant material like that, but I guess one just has to try. It doesn't say if these were irrigated. Oftentimes, when I read a study, they put in some native plants, walk away, come back a year later and when they're dead, call them failures. However at grade, we give a prairie 3-5 years to establish, which is a much kinder environment. The Ecology of using plants from single plant community is a cool idea, since who knows how these plants are interacting with each other. I look at his research and I ask this, what if the natives were planted into a completely established Sedum? Would the survival rates have been higher? The Sedums hold moisture, while blocking sunlight from hitting the media.

Here's some photos of green roofs I'd like to share, Sedums in extensive and semi-intensive roofs. They grow quite differently! And a shot of Eragrostis spectabilis grass in flower. More people should grow it, it likes hot, dry, sand. Prolific self seeder. Here's one of some colorful huge moth on a Coreopsis palmata.

[Weiser]

Might I suggest looking at Stipa hymenoides (syn. Achnatherum hymenoides & Oryzopsis hymenoides) Indian Ricegrass. It has a large native range across the western North America and is very drought tolerant tufted grass. (photos below)
Another good choice for a shorter tufted effect would be Bouteloua gracilis, Blue Grama also drought tolerant.