Horticulture science recognizes five outstanding plant species for green roofs

Green roof module planted with blue grama grass in the first season of the trials. Photo by Jennifer Bousselot.

American Society for Horticulture Science January 16, 2011, press release:

Used throughout the world to lessen the environmental impact of urbanization, green roofs can offer a wide range of ecological and aesthetic benefits. A new study from researchers at Colorado State University’s Department of Horticulture and Landscape Architecture published in HortScience evaluated six plant species to determine the plants’ ability to thrive on extensive green roofs in Colorado. Five plants that survived the two-year experiment are recommended for use in semiarid regions.

Extensive green roofs are characterized by shallow-depth (typically less than 15 than centimeters deep) growing media. Previous research on species that can survive and thrive on extensive green roofs has shown that succulents outperform most non-succulents. Jennifer Bousselot, who led the Colorado study, noted that other green roof studies conducted elsewhere in the United States evaluated nonsucculents that were “typically native to areas with high annual precipitation and relatively deep soil profiles.” The CSU researchers postulated that plants native to the Rocky Mountain region, especially those that inhabit areas with shallow, rocky, well-drained soils, may be better suited for use in extensive green roof systems. According to Bousselot, until this study extensive green roofs have not been scientifically evaluated in the high-elevation, semiarid climate of Colorado.

Though visual assessment and visual ratings have traditionally been used for measuring plant success on green roofs, these methods are usually subjective and not quantitative. To obtain more accurate data, the Colorado State University scientists compared digital image analysis data (DIA)—a process that incorporates periodic photographing of plants and digital analysis of the images—with manually collected converted two-dimensional data (C2D). The team determined that DIA and C2D are both useful for quantifying plant cover. “The DIA analysis appears to be a reliable substitution for the less accurate C2D method. Additionally, DIA can be used to estimate biomass accumulation, specifically for groundcover species.”

The researchers examined plant area covered for six species. Plant cover increased for all six during the 2008 growing season, but one species, Kannah Creek Buckwheat, experienced low winter survival and was removed from the study in 2009. Of the remaining five species evaluated, blue grama and hardy ice plant outperformed small-leaf pussytoes, brittle pricklypear, and spearleaf stonecrop. Bousselot noted that because five species survived over the two years of this study, these species should be considered for use on extensive green roofs in semiarid regions.

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The complete study and abstract are available on the ASHS HortScience electronic journal web site: http://hortsci.ashspublications.org/cgi/content/abstract/45/8/1288

Founded in 1903, the American Society for Horticultural Science (ASHS) is the largest organization dedicated to advancing all facets of horticultural research, education, and application. More information at ashs.org

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Professional video illustrates all smart water practices: green roofs, rain harvesting, stormwater retention, conservation

USEPAgov | December 20, 2010 | In 2010, EPA’s Office of Water produced this 11-minute video which highlights innovative efforts by green builders in Philadelphia who are helping protect and restore environmental quality and beautify the city.
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Taxes, fees and water rates across the country reflect cost of stormwater management

Last month we received notice of a new annual fee for stormwater management from our local department of public works. Whether the cost shows up in your utility bill, property taxes or as regional fees, you’re likely to be paying more. Following is a news story on the subject. ~ JB

Candaceadorka | November 1, 2010 | Chances are you’re paying more and more to deal with storm and sewer water. Experts say green infrastructure is a better way to spend those dollars.
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A video update on the Chicago Botanic Garden’s North Green Roof Garden

(See this green roof’s first video report here.)

chicagobotanicgarden | October 8, 2010 | Richard Hawke, plant evaluation manager, shows us how the Josephine P. & John J. Louis Foundation Green Roof Garden North is growing one year after the opening of the Daniel F. and Ada L. Rice Plant Conservation Center.
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Green roofs more logical than repeated resurfacing with shingles, other advantages provided, too

wilsonjd9 | September 12, 2010 | Get all the details at http://www.TheSolarVillage.com. The green roof system reduces heating inside the home or building by up to 30-40% making it a natural air conditioner. Green roofs are found in 20% of the homes in Germany.

The award-winning Wilson Natural Home above uses a green roof to both cool in the summer but also to improve insulation levels for improved warmth in the winter. The six inches of soil and several layers of membranes significantly increase the insulation levels in the roof which is a major contributer to heat loss.

The use of green roofing replaces soil that is displaced during construction. The return of native plants to the construction site returns the health of the local environment. Green roofs have been proven to significantly reduce the heating effect typical of homes, buildings, cities and towns caused by their dark roofing materials that absorb and then radiate heat into the local environment.

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Manhattan’s highest urban vegetation: Columbia University researchers study green roof use

Press the floating start button for a 2-1/2-minute video overview of a National Science Foundation-sponsored study of green roof systems covered with a waterproof membrane, a growing medium and vegetation. Environmentalists have long touted the benefits of green roofs, which they say include cooling the environment, and helping to absorb CO2.
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Philadelphia goal: Greenest City in America; green roofs key

“The legislation I signed into law today will help Philadelphia become a city of the future and set an example for others throughout the country,” declared Philadelphia Mayor Michael Nutter on May 18, 2010. The law to which Mayor Nutter refers requires installation of energy-efficient reflective roofs or green roofs on all new no- and low-slope roofs throughout the city. Read more here.

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