Green Roofs Guest Blog

Is it Time to Rethink Green Roof Planting?

      Latest research suggests sedums may not be best

This is the first Guest Blog from Tijana Blanusa,  a  researcher  at the RHS who specialises in Sustainable Gardening.

I recently published the results of my research that sedums may not be the best performers for helping cool air temperatures in the online journal Building and Environment.

The research1, carried out with funding from the Royal Horticultural Society (RHS) and Fundacao para a Ciencia e a Tecnologia (Portugal), looked at the possibility of using different plants for green roofs. The most popular currently used is Sedum but the researchers also looked at Stachys byzantina, Hedera hibernica and Bergenia cordifolia.

Enhancing a city’s green infrastructure is often considered a means to help address a number of environmental problems associated with built-up areas. It is now accepted that air temperatures in urban areas are higher than in surrounding rural areas, a phenomenon called the ‘urban heat island effect’.

This increase in air temperatures is largely due to vegetation being replaced by dark and impervious surfaces. Increased vegetation can, therefore, help reduce urban temperatures and also reduce the energy needs of buildings through their insulating properties. In Northern Europe vegetation is considered vital to reducing air temperatures on a city-wide scale.

The research looked at three key factors:

  • the effect of water availability on each of the species’ and leaf-surface temperatures;
  • the ability of each type of plant to reduce air temperatures above the canopy; and
  • the effect of these plants on ground cooling, and therefore potentially on the cooling of the building.

The research showed significant differences in the leaf temperatures between the plants. Sedum byzantina, for example, had the lowest leaf-surface temperature when exposed to high air temperatures on clear sunny days.

Based on the results of this work, I would suggest that choosing which plant to use on a green roof should not be decided entirely on what survives in a shallow substrate. Building designers should give greater consideration to supporting those species that provide the best all-round environmental benefits. This may mean introducing some form of irrigation system and deeper substrates to grow in – which in turn will have an effect on structural-strength decisions.

Previous research in the UK, based on model predictions, has shown that increasing green space such as parks, gardens and green roofs by 10 percent would reduce summertime air temperatures in the region of four degrees2.

With the climate getting warmer, gardeners and architects will play an even more important part in helping reduce the effects. Getting planting right in urban spaces, which can be very limited, is particularly important.But the advantage is that it not only can have a major effect in helping reduce urban temperatures but will also provide other environmental benefits – such as increased biodiversity and the collection of excess intense rainfall, thus lowering flooding risks.

Notes:

1 “Alternatives to Sedum on green roofs: Can broad leaf perennial plants offer better ‘cooling service’?” by Tijana Blanusa, M. Madalena Vaz Monteiro, Federica Fantozzi, Eleni Vysini, Yu Li and Ross W.F. Cameron. The report can be found at – www.sciencedirect.com/science/article/pii/S0360132312002132.

2 Gill SE, Handley JF, Ennos AR, Pauleit S (2007) Adapting cities for climate change: the role of green infrastructure. Built Environment 33; 115–133.

About the RHS

The Royal Horticultural Society is the UK’s foremost gardening charity, helping and inspiring millions of people to garden. They operate via gardens and shows and through  scientific research, publications, libraries and our education and community programmes. It is entirely funded by members, visitors and supporters.

Tijana Blanusa, the author of this blog, is pictured here on the Environmental section of the RHS stand at the Chelsea Flower Show.

RHS membership is for anyone with an interest in gardening. Support the RHS and secure a healthy future for gardening. For more information call: 0845 130 4646, or visit www.rhs.org.uk

About Fundacao para a Ciencia e a Tecnologia (Portugal)

 The Foundation for Science and Technology is the Portuguese governmental institution responsible for financing and evaluating scientific and technological knowledge, and aims to improve education, health, environment and the quality of life of the general public. Funding is given, subject to evaluation on merit, to proposals presented by institutions, research teams or individuals, and also through co-operation agreements in partnership with universities and other public

This post was written by:

- who has written 843 posts on My Climate Change Garden.

I am not an experienced gardener - more of an enthusiastic amateur who learns by trial and error and is keen to "manage" the effects of the weather on my garden. Writing this blog is my passion and I hope that it will continue to grow, allowing global gardeners to communicate about the effects of climate change on our plants and the future of our gardens.

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1 Comments For This Post

  1. SUSAN HUNTOON Says:

    I HAVE LIVED IN MONTANA,USA, NOW FOR ABOUT 8 YEARS. I AM AN AMATEUR GARDENER AND AM JUST REELING FROM THE CHANGE IN MY GARDEN. THE WEATHER PEOPLE HAVE COMFIRMED WHAT MOST OF US ALREADY KNEW, WE ARE IN AN EXTREME DROUGHT. OUR WATER RATES HAVE SKY ROCKETED ALSO. LAST YEAR, FOR 3 MONTHS MY WATER BILLS WERE OVER $200 AND ONE MONTH WAS OVER $300. I CAN NO LONGER AFFORD TO WATER MY YARD. BETWEEN NO RAIN AND THE WINDS, I HAVE LOST PROBABLY 20 PERCENT OF MY GRASS, THE GROUND IS LIKE POWDER, AND COME SPRING, IF THERE HAS BEEN NO MOISTURE TO SPEAK OF, I AM FIGURING MOST OF THE REST WILL JUST BLOW AWAY.
    I AM RETIRED AND LIVING ON A FIXED INCOME SO I CAN NOT AFFORD ANY MAJOR RESTORATIONS. WHAT I AM HOPING FOR IS INFORMATION ON HOW TO START CHANGING MY LANDSCAPE FOR THE NEW NORMAL, VERY LITTLE WATER AND WINDS. WE ARE HIGH PRAIRIE, ELEVATION 3500, IN A SMALL TOWN CALLED LAUREL, IN SOUTH CENTRAL MONTANA. I HAVE A LARGE CORNER LOT THAT MY HOUSE SIT IN THE MIDDLE OF SO I ACTURALL HAVE 3 YARDS. ALSO, I WANTED TO MENTION SOMETHING THAT I HAVE NOT FOUND ANY MENTION OF ANYWHERE I HAVE LOOKED. MY PLANT’S LEAVES ARE ACTUALLY BEING BURNED, BY UV RAYS OR WHATEVER. AT FIRST I THOUGHT THEY NEEDED MORE WATER, BUT IT DID NOT HELP. IT IS ACTUALLY THE SUN BURNING THEM. ELDERBERRY BUSHES, PLUM TRESS, PHLOX AND EVEN MY ELM TRESS. IT IS SCARY.
    I AM SORRY TO GONE ON SO, BUT THESE THINGS HAVE BEEN WEIGHING ON MY MIND.
    WHAT I AM LOOKING FOR IS INFORMATION, WEB OR BOOK OR JUST WHERE TO START LOOKING FOR THAT INFO. IF YOU ANY IDEAS, ANY, PLEASE RESPOND, SINCERELY, SUSAN HUNTOON

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