Potential green roof plants

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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?

Comments

Tim Ingram's picture

Tim Ingram (not verified)

Mon, 02/18/2013 - 1:58am

Wow - if only we could grow those plants like that here; wonderful pictures. Some are grown in the UK but I've never seen such strong and striking plantings and they must need that summer heat that we just don't get. I wonder if grown on a covered Mediterranean bed like I have read of by Dwight Ripley in the 1940's that they might grow and flower like that - they do seem potentially ideal plants for the heat and exposure of a 'green roof'.

Gordon Tingley's picture

Gordon Tingley

Mon, 02/18/2013 - 3:32am

Lori- thanks for posting that link! I now have a few more species and hybrids to track down..... as well as several more genera to find and test in our environment. At the moment though, just waiting for the wind and snow from this latest storm to die down.

ClifflineGardens's picture

ClifflineGardens (not verified)

Mon, 02/18/2013 - 6:40am

Delosperma nubigenum is an ok green roof plant in the Chicago climate, dies out in a harsh winter, and at least dies back. I've got it growing in here and there. The stunning flowers and toe-like foliage make an interesting enough plant that I've got it growing on my windowsill.

D. cooperi is not hardy in our climate, it vanishes in our winter. It can survive in Carbondale IL z6.

Zone limits are problematic in my experience, if one had a microclimate situation it might live. My instinct would be to throw many propagules on a roof, and if interbred, cold hardiness should arise. Denver is z5 and z6, if you're growing it in z5 it must be Chicago winter wet which kills it.

ClifflineGardens's picture

ClifflineGardens (not verified)

Mon, 02/18/2013 - 7:08am

Bulbs work very well on a green roof, they do come up as dwarfs though. Which is fine. As for those other species, I will have to start reading up on them. Lupine perennis failed at Chicago Botanic garden's green roof in multiple media depths. Its funny what will succeed. I've seen dandelions fail on extensive roofs, which is actually satisfying when I find them dead.

Gordon Tingley's picture

Gordon Tingley

Mon, 02/18/2013 - 8:01am

I'm surprised that Delosperma cooperi doesn't survive your winters. We have pretty wet winters here and although it may come out of winter looking a bit scruffy, it seems to come back. Some plants which don't relish wet winters can be given a helping hand by providing extra sharp drainage.... so that moisture never lingers too long during the season.

A few other plants to look into might be Anthemis biebersteiniana, some of the Helianthemums, and perhaps even a few dwarf cultivars of Lavandula angustifolia (soil depth requirements of the latter one may rule it out). Anthemis biebersteinianaprovides both foliage and floral impact. The leaves are like miniature silvery ostrich plumes, and the bright yellow daisy blooms add a nice contrast. Helianthemums have been used in parking strips in the Pacific Northwest. They are hardy to zone 4, withstand drought and poor soil. Flower color ranges from whites and yellows through pink, orange and red.

Another plant that might be a suitable candidate is Digitalis obscura. A Spanish member of the genus, it is a dwarf, semi evergreen plant that seems to be reliably perennial here in Nova Scotia, and in colder regions as well. The rusty copper blooms are nice, and the foliage is unlike most othe members of the genus.

Tim Ingram's picture

Tim Ingram (not verified)

Thu, 04/25/2013 - 9:54am

Some good little cushions there. It just made me think - I wonder if anyone has tried constructing a vertical rock garden on the side of a building? It could be quite a project in the right situation, a little like some of the amazing constructions of Harry Jans using tufa. Watering would be the key and Harry incorporates this into his tufa columns.

ClifflineGardens's picture

ClifflineGardens (not verified)

Fri, 04/26/2013 - 8:29am

I could envision something like that as a tile, with a more dense backing and fiberglass reinforcing. In a freeze thaw climate, problematic, due to falling hazards. The trick for American architects is to create something that is easy to specify. Build in the irrigation, and the attaching mechanism, keeping the weight low with perlite or ESCS. It would need to slope inwards with greater height.

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