Plant selection depends on the design intent for the roof, the climate and microclimate, irrigation, maintenance constraints and the depth of media. Shallow (less than 5 inch deep) roofs without irrigation will have a relatively limited palate of plants that can be used including sedums and a few other very drought tolerant species. As roof media depth is increased the roof becomes more garden like and can support a broader range of plant species. Intensive roofs with media depth greater than 1-3ft can support trees and shrubs as well as herbaceous annuals and perennials. More complicated plantings will increase maintenance and management requirements including the use of irrigation.