Plants for Green Roofs

Trees and Shrubs

• Green roofs generally fall into two categories, intensive and extensive. Intensive green roofs draw their name from the more intense labor required to establish and maintain the area. Trees and shrubs are part of intensive green roofs, and require extra substrate that simpler plants do not. Trees should not grow too tall, as the roof will fail to support the plant after awhile. Evergreens kept short by pruning, ornamental trees, rose bushes and azaleas are all common green roof trees and shrubs. Look for plants that do well in plenty of sun, as most roofs will not have much shade unless the building is surrounded by taller structures. Think about your area's climate and rainfall when selecting trees and shrubs. Generally, if the plants work well in your area under traditional garden conditions, they can thrive on a green roof.

Herbs and Mosses

• Extensive roofs are at the opposite end of the spectrum from intensive models. They require much less care and are often less expensive because the soil levels need only reach around 3 inches. The trade-off is a much more limited plant selection. A variety of herbs and mosses work well for green roofs. You can create an active and fragrant herb garden on a green roof by planting basil, lemongrass, oregano, chives and mint, all of which will tolerate green roof conditions well. Sheet or rock cap moss also provides a nice ground cover for an extensive green roof.

Flowers

• Flowers often are part of green roofs, but the varieties available to you depend on whether you have an extensive or intensive setup. Plants that require deep soil and regular watering should only be considered for intensive green roofs. Extensive roofs are a better home for prairie and wild flowers, which are adaptable to sunny conditions and irregular watering. As with trees and shrubs, look for plants that do well in your area and are accustomed to sunny conditions. Also, consider the blooming patterns and colors of the flowers you select. Flowers are most likely to provide different pops of color on the roof, and a variety of plants will give you a colorful green roof. Your local gardening center can give you advice on plants that meet these criteria.

Ornamental Grasses

• Ornamental grasses, such as perennial fountain grass, ribbon grass or rabbit's tail grass, add in splashes of greenery to green roofs. Grasses tend to require less care than flowers or trees and often perform well in very sunny conditions. They also tolerate a variety of soil and moisture conditions well, making them ideal on green roofs. Ornamental grasses can be part of both intensive roofs that have extra soil depth, and extensive roofs with shallow soil levels.