Heavens above – rooftop gardening

Heavens above – rooftop gardening

Steven R. Lorton

Rooftop gardens in San Francisco and Seattle provide down-to-earth lessons in container gardening

Look up, way up, along the skylines of San Francisco and Seattle. You’ll see tufts of green and tiny spots of color. People are gardening up there – people like Rosalie Ross Sennett in San Francisco and Dalmen Mayer and John Fikkan in Seattle, who have turned barren rooftops into verdant gardens. While these high-rise gardens are as varied as most earthbound plots, they all have one thing in common: the plants must grow in some kind of container. We climbed up to a few rooftop gardens and discovered good ideas that can benefit anyone who grows plants in pots.


When Rosalie Ross Sennett relaxes in her garden, hummingbirds whiz past her ears and bees buzz over the large, colorful blooms she cultivates. While birds and bees are common to many gardens, they are especially welcome in Sennett’s rooftop courtyard on a three-story building in downtown San Francisco.

Even if this garden were on the ground, it would still be extraordinary for its variety of plants: more than 130 shrubs, trees, and flowering plants – all in pots – thrive in the 28- by 30-foot courtyard.

Japanese maple, ginkgo, pomegranate, and other trees, as well as shrubs such as camellia and jade plant, add texture. For dashes of color, Sennett uses cosmos, geraniums, and salvia.

Perhaps most impressive are the 32 bamboos, some as tall as 15 feet. She grows about a dozen kinds, including running types such as dwarf whitestripe and giant timber bamboo, and clumping ones like Mexican weeping bamboo. Growing running types in pots keeps them on good behavior. Left unconfined in a garden bed, their invasive rhizomes (underground stems) pop up wherever they stray. Sennett especially likes the way the bamboos wave gracefully in front of all those high-rises. “That’s what makes them glorious,” she says.

Sennett uses a commercial potting soil (a mixture of sandy loam, composted manure, and lava products). She feeds the plants about three times a year with a solution of 15-30-15 fertilizer. She had a drip-irrigation system installed, with spaghetti tubing that feeds into each pot. Adjustable emitters at the ends of the feeder tubes regulate the water the plants receive. In especially hot weather, Sennett also spot-waters by hand.

She removes dead leaves and blossoms whenever they catch her eye. When it’s time to thin older bamboo plants, she uses the culms (stalks) and twine to brace the stems of other plants against the wind funneled into the courtyard by nearby buildings.


Dalmen Mayer turned a horticultural whim into gardening magic – on an 81-square-foot deck outside a fourth-floor condominium in Seattle.

At one corner, he first laid down a 1/8-inch base of rigid aluminum 30 inches square over the deck surface. Atop this he mounded pea gravel to a height of about 5 inches in the center. He set some lava rock into the gravel, which he then covered with potting soil. In this loose medium, he planted assorted succulents, including sedums and sempervivums.

Mayer then planted tiny clumps of black mondo grass (Ophiopogon planiscapus ‘Nigrescens’) from 2-inch pots. Next he added three little shore pines (Pinus contorta); he dips their tops back in bonsai style. When he found a moss he liked, he tucked it along the shady side of the garden. On the sunny side, he planted jewel mint of Corsica (Mentha requienii).


On his deck overlooking Pike Place Market in Seattle, John Fikkan created an ever-changing show of blossom and foliage, color and texture. The garden’s skeleton is, basically, evergreen. A big New Zealand flax (Phormium tenax) and a large lavender (Lavandula latifolia), which was chosen for its broad leaves and big bloom spikes, anchor the garden. Assorted ivies spill out of containers.

Two deciduous vines twine along the deck rails. Perennial hops (Humulus lupulus) burst out of a container and scramble along one rail each spring. On another rail, Virginia creeper (Parthenocissus quinquefolia) climbs along, producing soft spring foliage, lush summer leaves, and brilliant autumn color.

Fikkan chooses seasonal fillers for their ease of care and long bloom periods. He moves pots around and stages them for maximum effect.

In spring, cyclamen, primroses, and bulbs take center stage, accented by forsythia, or other spring-blooming shrubs, in 1-gallon cans.

In summer, annual standbys come out in full force: geraniums, impatiens, lobelia, marigolds, petunias, zinnias, even a few pots of dwarf sunflowers.


Consider the microclimate. North- or east-facing decks favor shade plants; south- and west-facing sites favor sun-loving plants, unless some shade is manufactured by a trellis, an arbor, or an awning. Temperatures normally drop faster the farther from the ground you are. Frosts come earlier, so marginally hardy plants are more vulnerable. High above the city, winds can be brisk. Tulips and long-stemmed daffodils can be reduced to a pile of petals with a couple of strong gusts. But sword ferns, zinnias in a pot, or a stocky form of Shasta daisy will stand up to a gale.

Exposed to full sun and drying winds, pots quickly lose moisture. Keep potted plants well watered – never let them dry out.

Consider the weight. If you are planning to use a lot of pots, or several big ones, weight might be a consideration. If you’re in doubt about the strength of a roof or deck, consult a structural engineer.

Check out the rules. If you live in an apartment or condominium, consult with the manager or condominium association. Rules vary: some buildings have no restrictions; others do not allow overhanging plants or water features; a few do not allow gardening at all.

Choose the right plants. Many perennials do well in pots and will take the extremes of high-rise living. Choose plants for their sturdy, handsome foliage, and consider the bloom a bonus.

Vines do well in big pots. Climbing a wall or trellis or running along a rail, they can add color, provide shade, and create a privacy screen. Akebia (A. quinata), clematis, climbing roses, grapes, and wisteria can all be grown successfully in generous containers.

Care for container plants. Repot perennials every couple of years. Refresh soil in annual pots yearly. If the soil has not compacted, you can reuse it; just add organic matter and mix in some granular plant food, well-rotted manure, or controlled-release fertilizer.

The trick to keeping a small tree happy in a container is root pruning. Every three years, pull trees out of their pots between late November and early March. Pull the big roots away from the rootball and cut them back. Then replant the tree, adding new soil. Scatter some controlled-release fertilizer on top of the soil and water well. In the spring, new feeder roots will shoot out to support the tree.

COPYRIGHT 1997 Sunset Publishing Corp.

COPYRIGHT 2000 Gale Group