Potential green roof plants

[Gene Mirro]

Clarkias, poppies and many other annuals will self-sow so thickly that the plants will be too crowded to bloom.  In the garden, I can just thin them with a hoe.  Not sure how you would handle it on a roof.

[Gordon]

Quote from Greenroofer

Nova Scotia contains zone 6b? Thats wild, must be the ocean currents? I went to school in Carbondale, Illinois and that was zone 6. Which is 6 hours south of Chicago by car.

Actually, the extreme south of Nova Scotia is zone 7A. Not many folk realize we are as far south as roughly Eugene Oregon, or Marseilles, France, but without such mild weather. Yes, the ocean and Bay of Fundy moderate the influence of the rest of the continent, but we sometimes still get winter blasts.

Clarkia would likely perform well as a green foof plant. I wonder.... if you are looking for something in a bit different hue- would Lithodora survive where you plan to use it? Lithodora Grace Ward is a stunner when in bloom.

[GreenRoofer]

A green roof plant is described thusly;

1) drought tolerance (xeritolerance)
2) preference for gritty soils with perfect drainage
3) low nutrition needs
4) full sun
5) not tap rooted, media depths are inadequate to make this adaptation useful
6) prostrate or wind adapted
7) cold hardy one zone beyond that in which it is planted, zone lowered with greater height
provides soil cover, or has a stunning flower as an accent plant

Many people try to point to barrens, glades, or cliff lines as being similar to a green roof. Take one of those ecosystems, remove 100% of the fractures in the rock into which roots might generally grow, and elevate it 15 - 650 ft in the air with shear drops on all sides and you have a green roof. Media depth is generally from 3 1/2 - 8 inches. 3 1/2 supports various succulents, mostly sedum. 5 - 7 supports prairie. >7 can support larger species like shrubs. 80 - 90% fired ceramic aggregate as media, 20 - 10% long term stable organics.

What plants grow in your gardens, that just refuse to die? When you bake them in the hot sun, and forget to water them, and they send up bright and happy growth regardless? Plants which grow and provide cover where nothing else could thrive, in just a few inches of grit? What serves you selflessly no matter the droughts you face? Tell me the names of these plants, for they are very...precious to me.

[GreenRoofer]

Lithodora seems to have average water needs, which is beyond a green roof. I love plants of the Boragincaceae though, and would love this gem in my own future rock garden.

[Gene Mirro]

The first thing that pops into my mind is plants that store food and water:  cacti, bulbs, taprooting plants.  Have you tried tulips and crocus?  How about the dryland native bulbs of the western US, like Brodiaea?  You said taprooting plants aren't a good choice, but I would give these a try:  Lupines, poppies, Mentzelias, Platycodon, Gentiana septemfida.  There is also a huge range of spring-blooming annuals from California that might work.  How about the strong-growing rock plants like Dianthus deltoides, Helianthemum and Iberis sempervirens?   The dwarf conifers are very tough plants.

[Gordon]

We have been playing around with one of the "Hardy Ice Plants"- Delosperma cooperi, it is tough as nails. This year we'll add another species to the mix D. nubigenum. Cooperi has such brilliant metallic hot pink blooms, and nubigenum adds equally bright yellow blooms to the palette. Naturally they wont be placed together, the colour contrast would be far too loud! There are several hybrids out there that are patented (such as the 'Jewel of Desert' series), meaning that propagation is an issue without prior agreement and royalties being paid. Delospermas have been extremely resilient plants for us. They propagate on a whim. We are on the lookout for new species to broaden the colour range available in this part of the world.

[Lori S.]

It would be nice if Panayoti himself could comment, but you'll probably find this interesting, Gordon:
http://prairiebreak.blogspot.ca/p/hardy-mesembs.html


Edit:  This is Panayoti Kelaidis' excellent gardening blog.

[Tim Ingram]

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]

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.

[GreenRoofer]

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.

[GreenRoofer]

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]

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.

[McDonough]

Just saw this on Facebook, this link should work for anyone whethjer on FB or not.
http://www.blipfoto.com/entry/2920895

[GreenRoofer]

a 'walk' through my ledge garden.

[Tim Ingram]

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.