Green Roof Plants
What plants are best suited to roof gardens?
Rather than selecting plants that can handle periods of drought and inundation, for a roof garden you must focus on plants that tolerate heat, dry conditions, and minimal maintenance. However, there is another crucial factor to consider when planting a roof garden.
Soil depth and weight considerations
Roof garden plant selection is intimately connected with the architecture and engineering of the building. The final weight of the growing medium and plants must be accounted for in the design of the structure.
Shallow green roofs are the lightest, but they require plants adapted to poor, dry soil conditions. These types of plants are best for inaccessible roofs that allow for minimal maintenance. The most common plants used in shallow green roofs are sedums and other shallowly rooted succulents.
If you double the depth of the planting medium (from 2 to 4 inches), you can use a greater variety of plants, including some native grasses and wildflowers. Go deeper any you can use even more types of wildflowers, but the increased weight is significant.
Minimal access, minimal maintenance
While there is a door leading to our green roof, the space is intended for limited traffic. A hose bib has been installed but we hope the plants will not need to be watered after they are rooted and established.
Source: http://greengarage.ca/greenroofs/plants.php (Site no longer exists.)