Cornus kousa, Kousa Dogwood Hardy to Zone 5
Kousa dogwood stays small for a tree, with some varieties maxing out at just about 30 feet, making it an excellent foundation planting for a rooftop garden. In spring, the tree has small but beautiful white flowers and pink bracts, which transition to deep green summertime foliage. Autumn offers its own benefits, with red-purple leaves and fruit
Corylus avellana ‘Contorta’, Harry Lauder’s Walking Stick Hardy in Zones 4-8
Corylus avellana ‘Contorta’ twists itself into seemingly unfathomable shapes that are good sculptural plant accents to a rooftop garden. The heart-shape foliage on the shrub or small tree, which can reach 10 feet tall is interesting, too.
Juniperus squamata, ‘Blue Star’ Juniper Hardy in Zones 4-8
Also called singleseed juniper, ‘Blue Star’ shines with skinny needles that have a definite silvery-blue cast. The dwarf juniper — which puts out mounds of needles on a shrub that reaches about 3 feet tall — is a good accent or container variety for rooftop gardens.
Chamaecyparis obtusa ‘Nana Lutea’, Dwarf Hinoki Cypress Hardy in Zones 5-9
Fanlike foliage and a yellowish-green color are two standout characteristics of golden dwarf hinoki cypress. Extremely slow-growing, the evergreen will reach only 3 feet tall at its mature height. It needs a regular watering schedule but is otherwise wonderfully low-care. The evergreen brightens corners on a rooftop garden or works well with other plants in container combinations.
Astilbe ‘Fanal’, Fanal Astilbe Hardy in Zones 3-8
Great for shadier spots on a rooftop, ‘Fanal’ rewards gardeners with rich crimson color that blooms midsummer (typically July). A good perennial plant for the middle of the border, astilbe shoots up stalks of about a foot-and-a-half. It does best in moist soil; don’t allow astilbe to dry out.
Hosta ‘Big Daddy’, Big Daddy Hosta Hardy in Zones 3-8
Integrating impressively sized hosta into shadier spots on a rooftop garden is a terrific way to add beautiful foliage to the space. ‘Big Daddy’, is just one choice; its blue-green leaves offer rich, deep color and are big enough to cut as foliage for bouquets — perfect for multitasking rooftop gardening plants.
Ajuga reptans, Ajuga Hardy in Zones 3-9
A groundcover that is attractive to butterflies and hummingbirds, Ajuga reptans, needs water on rooftops but rewards with steady growth. ‘Silver Beauty’ is one good choice, as is ‘Bronze Beauty’, which has deep blue flowers and bronze-tinged foliage.
Lavandula angustifolia, Lavender Hardy in Zones 5-9
Beloved for scent, lavender is a member of the mint family and native of the Mediterranean, so it weathers the windy and dry conditions of a rooftop garden well. Its beautiful, gray-green foliage reaches heights of about a foot and a half, making it a good fit for either containers or full-fledged rooftop garden beds.
Hemerocallis ‘Anna Warner’, Daylily Hardy in Zones 3-9
Most daylilies are fairly hardy, and their consistent blooms mean that they offer rooftop gardeners a good way to add color. Try Hemerocallis ‘Anna Warner’, which has pinkish-lavender blooms and does well in full sun. Strappy foliage reaches about 2 feet in height, and the plant thrives in a huge zone range, so you can enjoy it just about anywhere.
Stachys byzantina, Lamb’s-Ears Hardy in Zones 4-10
A nice fit for low-growing borders or the front of flower beds, lamb’s-ears, has a distinctive soft, feathery feel to the silver-gray foliage. In the ground it tends to spread, so it may be best for containers on rooftop gardens. If the purplish blooms get leggy in summertime, cut them back.
Lonicera x heckrottii ‘Gold Flame’, Gold Flame Honeysuckle Hardy in Zones 5-8
A cascade of ‘Gold Flame’ honeysuckle is a great way to attract hummingbirds and butterflies to a rooftop garden. It begins blooming in late spring, with delicate pale pink to deep magenta blossoms that are incredibly fragrant. Honeysuckle vine reaches about 20 feet in length, making it a good fit for a trellis or above a rooftop porch structure.
Hydrangea petiolaris, Climbing Hydrangea Hardy in Zones 4-8
Creamy white blooms decorate the vines of this self-adhering plant, which can reach an astonishing 60 feet long. However, climbing hydrangea is easy to prune and rewards with those springtime flowers as well as a stunning autumn color transformation, when the green leaves turn to a bright yellow.
Festuca glauca, Blue Fescue Hardy in Zones 4-8
Ornamental grasses — hardy, with few maintenance needs and year-round structure to boot — are a good fit for rooftop gardens, and blue fescue can be used in containers, in a border, or as an edging plant and reaches just 10 inches tall.
Miscanthus sinesis ‘Gracillimus’, Maidengrass Hardy in Zones 5-9
On the other size end of the ornamental grass-size spectrum, maidengrass towers and can reach heights of 7 feet. It does best in full sun and can be used in the back of a rooftop garden border. Or plant multiples in a row to block an unsightly view.
Article adapted from BHG online by Kelly Roberson, for full article http://bit.ly/MtoYTv