If you're ready to join the green revolution, transform your roof into a lush garden. Not only do green roofs -- also known as vegetated roofs -- look good, they help reduce noise and air pollution and help your roof last longer, all while lowering your energy bills. Extensive green roofs require planting media of less than 6 inches, so choose plants with shallow root systems; varieties that tolerate drought, sun and heat grow best on green roofs.
Succulents grow well in roof gardens; these drought-tolerant plants release less moisture through transpiration, or evaporation through leaf pores. Choices include ice plant (Delosprema cooperi), which grows to 6 inches tall and 3 feet wide. Ice plant blooms in summer with large, deep pink blossoms. It's hardy in U.S. Department of Agriculture plant hardiness zones 8 to 10, where it grows best in full sun. Myrtle spurge (Euphobia myrsinites) also grows well in sunny rooftop gardens. This spreading succulent has white-green foliage and blooms with clusters of yellow-green flowers and bracts. Hardy in USDA zones 5 to 8, myrtle spurge grows to 12 inches tall and 3 feet wide.
Ornamental grasses have shallow root systems and require little maintenance, making them a natural choice for green roofs. Selections include sideoats grass (Bouteloua Curtipendula), a sun-loving species that grows in 30-inch-tall clumps of blue-green foliage. Hardy in USDA zones 4 to 9, sideoats grass blooms in summer with purple inflorescences, followed by seed spikes that draw birds Praire junegrass (Koeleria Macrantha) also grows well on roofs. This North American native grows in clumps of tufted, light green foliage and blooms with silvery inflorescences in early summer. Hardy in USDA zones 3 to 9, this drought-tolerant grass reaches heights of 2 feet and prefers sunny sites.
Groundcovers grow wider than they do tall; their roots help retain moisture in the soil, preventing run-off. Drought-, heat- and sun-tolerant varieties suitable for green roofs include creeping sedum (Sedum spurium), a 6-inch-tall plant that spreads to 3 feet wide. Hardy in USDA zones 4 to 9, creeping sedum blooms with pink-red flowers in summer that attract butterflies. Cultivars include "John Creech," which has green foliage and pink blossoms, and "Fuldaglut," which has red-coppery foliage and red flowers. White stonecrop (Sedum album) grows to 4 inches tall and spreads to 14 inches wide, creating a mat of evergreen foliage that takes on a red tone in winter. Hardy in USDA zones 4 to 8, white stonecrop blooms with creamy blossoms in early summer.
Not many perennials tolerate the shallow planting depth common to green roofs. Exceptions include yarrow (Achillea millefolium). This drought-tolerant, sun-loving native perennial grows to 2 feet tall, forming a carpet of aromatic, gray-green foliage. Yarrow blooms in summer with clusters of white flowers and is hardy in USDA zones 3 to 9. The lance-leaved coreopsis (Coreopsis lanceolata) adds bright yellow color to the summer roof-top garden. This North American native grows to 3 feet tall and attracts butterflies. It's hardy in USDA zones 4 to 9 and thrives in sunny, dry sites -- like your roof.