As the shift to provide services such as storm water management and evaporative cooling with plant based systems like green roofs gains momentum, the question arises, what plants best provide these services?
What are these plants? Are they native plants to the region? Are they plants selected to provide a specific function regardless of their origin? What kind of maintenance will they require? How will they affect area outside the perimeter of the roof and the surrounding ecology? Will the cost of these plants allow the system to operate competitively with mechanical systems?
As a nurseryman specializing in green roofs I have had the opportunity to observe in the field the plants on green roofs. I also receive feedback from university research and landscape designers as well as installers and maintenance professionals.
As a nurseryman specializing in green roofs I have had the opportunity to observe plants on green roofs. I also receive feedback from university research and landscape designers as well as installers and maintenance professionals. In general green roof plants have fibrous roots systems, are long lived, drought tolerant, and should not be invasive to the greater landscape.
The main ecosystem services provided by green roofs are; storm water management; evaporative cooling; providing habitat for insects, birds and other small creatures and providing aesthetically pleasing sights on buildings.
The main purpose for green roof installation in the US is for storm water management. Plant selection for this function has to conform to several conditions. These most commonly include shallow media depth, mineral media composition and tight budgets. Plants that can without irrigation and little fertility best fit these conditions. Plants that are succulent in nature or have other drought strategies are most commonly used.
In order to get evaporative cooling from a green roof plants must be actively pumping water through their vascular system to the leaves. Plants that have a dormant period or plants that have CAM metabolism may not be suitable if this is the primary goal. Irrigation may have to be installed to assure a steady supply of water.
In order to provide habitat on a roof plant selection will have to be targeted to fauna and then the proper media depth and composition will have to be supplied. Monarda fistulosa is a good food source for pollinators in the eastern US but likes to be in windy areas and likes lean soils.