Guelph Study May Grow More ‘Green’ for Green Roof Suppliers

April 29, 2013 - News Release

A University of Guelph study on how substrate pH affects a popular plant in “green roofs” is already proving a boon to local growers and green roof plant suppliers.

The study, “Optimal Growing Substrate pH for Five Sedum Species,” was published recently in the agricultural journal HortScience.

In the study, researchers led by Prof. Youbin Zheng and research associate Mary Jane Clark, School of Environmental Sciences, looked at the effect of varying growing substrate acidity on sedums. This plant is a favourite for rooftop green space, as it withstands winter conditions and drought.

The market for rooftop plants in North America has exploded recently, as more buildings recognize their environmental benefits.

The team found optimal pH ranges for Sedum plants. Sedum plants within these ranges can grow many times faster than those grown out of these ranges. This is the first research to provide optimum growing substrate pH levels in order for growers to efficiently and rapidly produce good quality Sedum plants to meet the demand in many horticultural applications, including green roof plantings.

“Manufacturers had always followed the example of European manufacturers, who had gone with a pH level that was more alkaline,” explained Zheng. “But they found the plants weren’t growing fast enough. In our studies, we found the plants did not grow at that level as well as they would at a slightly lower level. But going too low with pH and making the substrate too acidic was also a problem. So we had to find the best levels for these plants to thrive.”

Industry partners Sedum Master and LiveRoof have used the study results in their facilities, said Zheng. Both companies helped fund the study.

“These plants are widely used in Europe, and there is more demand for green roofs in North America now,” he said. “In North America, installed rooftop areas had doubled from 2010 to 2011. Manufacturers were having difficulty making enough of the sedum to satisfy the demand. In most cases, orders would have to be placed months to a year in advance.”

Green roofs can help manage stormwater runoff, and they can help cool buildings in summer, reducing hydro costs substantially. Some municipalities have enacted bylaws, including Toronto in 2009, requiring green roofs on new developments.

“With the results of this study, manufacturers can produce sedum much faster,” said Zheng. “They don’t need as much lead time, and it saves labour, time and land space. As the need for green roofs increases, the market will grow, leading to more jobs and a thriving industry.”

For more information:

Prof. Youbin Zheng
Tel: 519 824 4120X52741

For media questions, contact Communications and Public Affairs: Lori Bona Hunt, 519-824-4120, Ext. 53338,; or Kevin Gonsalves, Ext. 56982,

University of Guelph
50 Stone Road East
Guelph, Ontario, N1G 2W1