This is sort of a supplement to another book, Planting Green Roofs and Living Walls by Nigel Dunnett and Noel Kingsbury (Timber Press 2004 ISBN 0-88192-640-X). It is, as the title claims, a compendium of suitable plants to grow on a roof. It also touches on the rationale behind this movement along with the challenges and techniques.
The genus Sedum is thoroughly represented as well as many of the other smaller succulents. There are also plants originating from an assortment of difficult sites from windswept shorelines to rocky alpine outcrops.
It is significant that the authors of Planting Green Roofs and Living Walls are Brits working in Northern Europe and that the authors of Green Roof Plants, a Resource and Planting Guide operate along the Mid-Atlantic Coast of the US. Both areas have summer rainfall and some degree of humidity. The rainy Pacific Northwest is a more likely candidate for green roofs but the Northern California coast with its summer fog is apparently getting a few green roofs as well.
After first seeing the book, Planting Green Roofs and Living Walls by Nigel Dunnett and Noel Kingsbury, I wondered what is the point of having plants growing on your roof? I was already used to the idea of frustrated urban gardeners creating verdant balconies and even lush roof top oases where they could step outside the confines of their apartments to cheerfully toil in the soil. I’m aware that there are even modern counterparts to the hanging gardens of Babylon bedecking the towering temples of commerce. I also recall reading about pioneers building sod-roofed cabins out in the vast American prairie.
Utilizing sod as a building material was out of necessity like the use
of adobe here in Spanish and Mexican California. Creating a garden
several stories above street level is usually a labor of love although
some degree of ostentation could also be a motivating factor. Several
decades ago in Brazil there was the multi-talented Roberto Burle-Marx
creating 2 and 3 dimensional cubist landscapes around and up into
modern public buildings making unrestrained use of colorful tropical
epiphytes.
I realized that a rooftop encrusted with plants would be cooler in the
summer. A city full of planted roofs would be cooler. This would save
energy. There would be long-term savings that would eventually offset
the initial high cost of installation. Other benefits being advanced by
the authors are the slowing of rainfall runoff along with the filtering
of pollutants, the absorption of carbon and the production of oxygen. A
habitat niche would be created for wildlife.
Plants on a roof would likely thrive or at the very least endure in
climates with summer rainfall and high humidity. But is this a viable
technique for California?
There are at least two projects by Rana Creek Restoration Ecology of
Carmel Valley that show that green roofs may work in at least the
coastal fog belt. They have installed a green roof on top of the Gap
Building in San Bruno. They are also in the process of installing
another on the yet unfinished Academy of Sciences in Golden Gate Park,
San Francisco. Over time it should become evident how well green roofs
perform in a drier climate.
Contributed by Angel Guerzon.
Green Roof Plants, a Resource and Planting Guide by Edmund C. Snodgrass & Lucie L. Snodgrass, Timber Press 2006 ISBN-13: 978-0-88192-787-0, ISBN-10: 0-88192-787-2
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