Researchers at Ontario’s Vineland Research and Innovation Centre are working towards an expanded palette of plants for green roof applications and increased opportunities for incorporating native plants in green roof installations, along with traditionally used Sedum species.

“The idea with our research is to find a range of native plants that would be suited to what I like to call ‘roofscaping’ and offer a broader range of plants for designers,” explains Dr. Rumen Conev, Research Scientist Ornamental Plant Breeding. “We are testing 23 native genotypes against the plant considered to be the industry standard, Sedum kamtschaticum. The goal is to find a range of native plants to complement Sedum plantings rather than offering the either/or alternative to industry.”

This two year-study initiated in 2011has a unique experimental design to ensure more reliable conclusions. “We have created a built-up system that is a complete replica of natural conditions,” says Conev. “We are comparing the performance of plants randomly planted in plots with four and six inches depth of mineral substrates on an existing roof in non-irrigation conditions and full exposure to sun and wind.” Conev is also partnering with Dr. Norman Goodyear from the Nova Scotia Agricultural College to conduct the same experiment but using local plants more adapted to the maritime climate.

Preliminary results have identified at least 21 species that perform from very well to extraordinary with no irrigation, and include a range of growth habits from completely prostrate ground covers to almost vertical grasses. “This will give an immediate opportunity for designers to make interesting combinations of plants,” says Conev. “We have also identified some plants that have the ability to grow more than 10 fold in one season.”

Most of the species also performed equally well in both the four-inch and six inch depth substrate. This provides a big advantage because growing in a four instead of six-inch depth reduces the weight load by about 25 to 30 pounds, has less structural engineering limitations and lower costs.

Once this phase of the project is completed, researchers will know which plants perform well under high stress and will be in good shape after a couple of years of growth. They will also have a good idea of which plant species are most successful in the two study areas. Conev adds that they won’t be able to predict if the plants will survive in other locations, and the plants will have to be tested in the area to be grown to know how they will perform.

Conev is also studying a few roofs with well established plants in Kitchener, Guelph and Toronto in order to assess environmental impacts. “We found a couple of species that do seed freely and the seeds can be spread by wind and germinate,” explains Conev. “If this occurs on the green roof it is not much of a concern, but if there are adjacent conventional roofs that are not supposed to have vegetation or existing landscaping or sidewalks, unwanted vegetation may result. We will be monitoring next spring to see if these volunteer seedlings successfully survive over the winter and become a problem next year.”

Next Step to Benefit Growers
Phase 1 of the project will be completed by the end of March 2013. However, Conev notes that they will not be able to give complete answers to all of the questions raised. Therefore, he is looking towards a second phase that will see the continuation of this experiment and other new ones.

“Phase 1 provided answers for green roof specialists and a range of native plants for selection,” explains Conev. “However, in order to boost the green industry, we also need to know more about propagation and production practices in greenhouse and nursery settings. We do know that all of the plants being studied can be propagated by seed, which will benefit greenhouse growers. And all of these plants can be propagated by at least one vegetative method, opening opportunities for nursery production as well.”

Conev plans to apply to the Canadian Ornamental Horticulture Alliance (COHA) for funding for the next step. He plans to work in collaboration with the University of Guelph next year on the production side, while he continues the genetics research.