High above busy streets, roof gardens are islands of green, cool calm, providing additional home space for entertaining, puttering or relaxing in a beautiful garden environment. Roof gardens in city areas help reduce temperatures and air pollution levels, but plants may have to cope with full sun and strong, drying winds. Plant drought-tolerant shrubs that can cope with air pollution and select varieties that will provide year-round interest and color. Brooklyn is suitable for U.S. Department of Agriculture plant hardiness zone 7 shrubs. Gardeners should check local ordinances and the weight-bearing capacity of the roof and use containers that are either heavy or well-secured.
As winter starts to relax its hold, flowering shrubs in roof gardens bear the promise of warmer days to come. Japanese quince (Chaenomeles japonica) provides orange-scarlet late-spring blooms, followed by small, greenish-yellow fruit. Flowers are borne on the previous year's growth, so plants should only be pruned lightly for shaping after flowering. Suitable for USDA zones 5 through 9, this deciduous shrub grows 3 feet tall and 6 feet wide. Viburnum "Conoy" (Viburnum × burkwoodii "Conoy") provides fragrant, white sprays of spring blooms. Hardy in USDA zones 5 through 8, this shrub grows 3-to-6 feet tall and 6-to-10 feet wide and suits container-growing. Both plants are drought tolerant.
After a long, hot summer day in the city, flowering shrubs enhance summer evenings spent in a roof garden. "Bicolor" crape myrtle (Lagerstroemia "Bicolor"), hardy in USDA zones 6 through 9, tolerates drought and city air and bears reddish-pink and white blooms from June to September. A compact plant, it grows between 2 and 4 feet tall and wide. Cotoneaster (Cotoneaster astrophoros) also tolerates air pollution. Flowering from May to June, it bears small, white, star-shaped flowers and grows 6-to-12 inches tall and 6-to-18 inches wide. Hardy in USDA zones 5 through 9, it also bears bright red berries that attract birds.
As the weather turns cooler, gardeners can still enjoy a roof garden floral display. Shrubby cinquefoil (Potentilla fruticosa "Coronation Triumph") has showy yellow flowers from spring to early fall. Growing 2-to-4 feet tall and wide, this tough, deciduous shrub is drought-tolerant and hardy in USDA zones 3 through 7. Prolific bloomer Ever Red loropetalum (Loropetalum chinense "Chang Nian Hong") has red flowers through all seasons except winter. Hardy in USDA zones 7 through 9, it grows 3-to-6 feet tall and wide and has year-round burgundy foliage.
Make your roof garden a four-season pleasure with plants that brighten the cold season. Two drought-tolerant shrubs that provide winter color are Japanese barberry (Berberis thunbergii f. atropurpurea "Harlequin") and American arborvitae (Thuja occidentalis "Bobazam"). Pollution-tolerant Japanese barberry grows 2-to-4 feet tall and 3-to-5 feet wide, is hardy in USDA zones 4 through 8, and provides attractive red berries to brighten winter landscapes. American arborvitae, aptly called Bowling Ball, naturally grows into an attractive globe of sage green, evergreen foliage. Suitable for USDA zones 2 through 7, it grows 1-to-3 feet tall and wide.
- Chicago Department of Environment: A Guide to Rooftop Gardening
- Cornell University: USDA Hardiness Zones for New York
- Missouri Botanical Garden: Berberis Thunbergii f. Atropurpurea "Harlequin"
- Missouri Botanical Garden: Chaenomeles Japonica
- Missouri Botanical Garden: Lagerstroemia "Bicolor"
- Missouri Botanical Garden: Cotoneaster Astrophoros
- Missouri Botanical Garden: Potentilla Fruticosa "Coronation Triumph"
- Fine Gardening: Viburnum × Burkwoodii "Conoy"
- Fine Gardening: Loropetalum Chinense "Chang Nian Hong" (Ever Red Loropetalum)
- Fine Gardening: Thuja Occidentalis "Bobazam" (American Arborvitae, Eastern Arborvitae, White Cedar)
- Photo Credit Ryan McVay/Photodisc/Getty Images