The sky is the limit when selecting plants for a green roof. Knowing the type of system and the soil depth is vital. Extensive systems where the soil depth is 4-6” or intensive systems where the soil deeper than 6” is the major deciding factor on what plants you decide to grow on your green roof. Robust and drought resistant plants are used for extensive green roofs whereas for intensive green roofs, there is an abundant array of plants to choose from. Having adequate water supply on the roof for intensive systems is vital, depending on the climate.
The first book I read on the topic over ten years ago, Green Roof Plants by Ed & Lucie Snodgrass described the best traits for green roof plants, “The most successful green roof plants are low-growing, shallow-rooted perennial plants that are heat, cold, sun, wind, drought, salt, insect and disease tolerate”. For this reason, many standard garden plants will not survive on a green roof. Ten years ago, almost all roofs were planted with sedum plugs or cuttings. Now, there are plenty of variations of plants being used, such as seeds, perennials, herbs, grasses, trees and pre-vegetated sedum mats, (like sod). Plants that thrive on green roofs include exotic and stunning species ranging from bizarre to beautiful. A few are even edible! Some of the plants mentioned carry out specific roles on a green roof. Those plants include:
Succulents – which form the bulk of your planting.
Grasses/Turf – they are great at covering a lot of territory. Some native grasses are used with sedums or perennials.
Wildflowers – these benefit from deeper soil green roofs.
Aromatic Herbs – if you want your green roof to change your green roof into a culinary garden.
Most green roof planting needs to be performed during the spring or fall. When planting in the summer, temporary irrigation is needed to allow for plant establishment.
Typically, extensive green roofs are designed to supplement storm water management, habitat creation and the reduction in the heat island effect. Intensive green roofs are rising in popularity because they provide pleasant views, healing gardens, vegetable gardens, urban gardens and useful outdoor space for building occupants.
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