Rooftop Gardening

Rooftop gardens take the enjoyment of plants to a new level. Cars rush by on the streets below while gardeners on rooftops and terraces enjoy the unusual perspectives offered by the setting. These gardens have a mood all their own. Because they are much smaller than the average back yard, they challenge gardeners to think about what is really essential, and the results can be unexpected and extremely striking.

Just like gardens on the ground, rooftop gardens are “an escape — an escape from everything else that’s chaotic,” says Bill Jennings, a garden designer in Kansas City. A rooftop or balcony garden demands a good design, he says. Pots and planters should be an appropriate size (bigger is better), and they should be arranged to take full advantage of the space and look attractive through the windows from inside. Jennings recommends simple containers. “If the container itself is simple, you can do some exciting things with the plants,” he says.

Jennings lines pots with coco fiber, which keeps the roots cool and provides insulation in the winter. He recommends soil-less potting soil mixes, which are lightweight and designed to both drain well and retain moisture.

Plants in rooftop gardens are exposed to more extreme conditions than plants in the ground, but many great garden plants will thrive if you choose carefully and take care of them. A watering can or a hose may be all you need, but consider installing drip irrigation, especially for large rooftop gardens. Here are some hard-working rooftop plants Jennings recommends:

— Trees: Choose smaller trees and little-leaf varieties, such as Amur maples, Japanese tree lilac (Syringa reticulata), Japanese maples, staghorn sumac, and crabapples. Trees and other tall plants may have to be tethered to railings to keep them from blowing over; bungee cords will do the trick.

— Evergreens: Pines, junipers, and dwarf conifers of all kinds do well in these conditions.

— Shrubs: Boxwoods, cotoneaster, Japanese kerria, hydrangeas, barberry, and yew are very tough.

—Roses: Roses of all kinds — including climbing roses — will thrive in pots in a rooftop garden.

— Perennials: Try hostas, ferns, astilbe, daylilies, lavender, yarrow, artemisia, and Russian sage. Smaller ornamental grasses add luxurious texture. Sedums and sempervivums are also great choices.

— Annual flowers thrive in containers with other plants, or in pots on their own. Some good choices are: zinnias, pentas, lantanas, marigolds, petunias, torenias, and impatiens. Annual vines, like cypress vine and morning glory, will grow rapidly and bloom through the fall.

— Vegetables: Tomatoes, cucumbers, peppers, zucchini, broccoli, and lettuce and greens are good candidates for pots. Herbs also thrive in containers. You could even grow strawberries and raspberries in big troughs in a rooftop garden.