Vestpocket forests ... in unusual places.

Urban trees can be found high and low in penthouse terraces, postage-stamp gardens, even alleys.

Before I began living aboard a sailboat on the Potomac river, I owned a condominium in a high-rise apartment building, the Richmond, six blocks from the White House. Flanking the building's entrance is a pair of junipers, now four feet tall, growing in concrete planters. One day, word spread that the Richmond's building manager, John Blizzard, had discovered a sparrow's nest tucked deep in the foliage of one of the trees.

"I didn't realize the chicks were there until I went to trim the branches," Blizzard recalls. "Those sparrows are industrious creatures, and they have an ideal camouflaged spot. The first year, they raised three broods. This year they moved to the other juniper, and so far they've had two broods."

When Blizzard planted the trees four years ago, he was told to purchase poodle-cut junipers. The trees have a tuft of branches toward the crown, then a section of trunk pruned bare, then another tuft of greenery. Those two junipers are card-carrying members of the urban forest, even though they don't provide the same level of benefits that more traditional trees do. Urban forest trees are doing their part to shelter wildlife, sequester carbon dioxide, scrub pollutants from the air, and soften the streetscape with soothing green.

Fig trees, cherries, honey locusts, ornamental pears, Indian hawthorns, Japanese yew pines, palms, European olives, crape-myrtles - almost any species can be found in cities, depending on the local climate. These miniature urban forests can be created next to pots of geraniums on the balconies of high-rise apartment buildings, alongside wisteria on penthouse terraces, next to morning glories along the edges of rooftop gardens above banks and restaurants, and, down at street level, in postage-stamp-sized gardens in front of or behind townhouses, and in back alleys transformed into pedestrian promenades.

There are many ways to bring trees into the urban environment - some more successful than others - depending on available space, water, drainage, structural integrity of the building, and microclimatic conditions. Potted trees are usually the least successful because of limited space for root growth.

Why do people plant trees and gardens in such unconventional places? One reason is to utilize land that can't be developed. In San Francisco, for example, many alleys and stairways are too steep for building streets but are perfect for planting.

But most importantly, these city gardens satisfy the need for a natural environment. In any area where buildings and concrete dominate, these small patches of green go a long way in providing city dwellers with a link to nature.

The urban forest has even sprouted at the marina I now call home. My neighbors on houseboats find that the decks fore and aft are ideal sunny places for growing flowers, herbs, tomatoes, leaf lettuce, and an occasional juniper or dwarf pine. Liveaboards Betty and Jerry Wesley place their prize hibiscus - a shrub on its way to becoming a tree - on the starboard side to help balance their 57-foot houseboat, which has a tendency to list to port. During a visit, they offered me a wild strawberry from one of their planters. In a pot next to the strawberries were chives they clip to dress up their scrambled eggs for Sunday brunch.

Sherry O'Connor, another boating gardener, asks, "Why should I bother about all that fertilizing and weeding? One reason is that if you grow it yourself, it tastes better."

Blizzard has his own postage-stamp garden at the house he rents, and the Richmond's residents appreciate the fresh flowers he places in the lobby every day. His garden, which has raised planting beds and an underground irrigation system, is less than one-fourth the size of a tennis court. He has a fig tree espaliered (trained to grow flat) against a south-facing brick wall, and radiant heat from the wall keeps the tree so hardy and vigorous that it produces hundreds of figs every year.

"Gardening is mentally and physically relaxing," says Blizzard. "It's a very basic thing to put things in the ground and have them come up. It keeps you attuned to the seasons."

In one of the Richmond's 10th-story penthouse apartments, condominium president Richard Beatty, a chemical engineer who sets up research projects between NASA and the Russian space program, grows junipers and arbor vitae on his terrace. Adding color are geraniums, impatiens, and violas, which produce an edible flower good in salads or floating in soups. Portulaca, a weed-like flower, has taken seed in the cracks between the terrace's paving tiles.

"Some people think it looks ratty, but I love it," says Beatty. "This is a balcony in a high-rise building, and growing stuff here is a matter of putting things in a pot and manicuring them. If I had a house in the country, I would let a lot of things grow wild. You can't do that on an urban balcony, but when stuff starts sprouting between the pavers, that's as close as you can get. I confess that I do pull out miscellaneous weeds, but anything that blooms I leave."

Connecting with nature is part of the magic of growing trees in difficult urban environments. Maintaining that magic was the main design goal for a garden created by landscape architect Greer Maneval, another marina neighbor and principal of Maneval and Associates. Along the edge of the garden, which surrounds a swimming pool, Maneval preserved existing mature trees and a tiny stream that flows into Washington's Rock Creek. The garden, measuring 30 by 50 feet - including pool, trees, and brook - was put in with a shoehorn. Besides saving the natural environment, the clients wanted privacy, recreation, and a place for entertaining.

Another client specifically wanted an urban retreat, a place where the couple - one an American Express executive and the other a World Bank official - could get together after work, sit down, and talk over their day. For their "outdoor room," Maneval selected evergreens and a triple-trunk crapemyrtle, chosen for its summer blooms and mottled gray and beige bark in winter. She had the house painted in a soft tone that provides a muted backdrop for the plants. Most are perennials; annuals are used as accents.

"All my clients are so busy," says Maneval, "that no one has time to do any fussing in a garden any more. Those people are rare when you find them. Most just want to go out on a Saturday morning in the spring, put in annuals, and be done for the year."

Maneval also designed a vestpocket public garden that connects the Richmond residential condominium with an office building owned by the National Wildlife Federation. Half of the garden is a paved plaza accented by two formal walkways of little-leaf lindens and containers of blooms. At lunch time, the benches are packed with office workers.

The other half of the garden is a lush lawn bordered by rose bushes and crytomeria, evergreens that grow to 20 feet in height. At the far end, near the Richmond, is a wisteria-draped trellis that leads into a secluded, tree-shaded refuge where I used to walk my cat. The garden was the deciding factor when I bought my condominium. It offers a quiet oasis only steps from the hubbub of a busy street of shops and sidewalk cafes.

Sometimes a shady spot for entertaining is the prime requirement in a small garden, and a large shade tree may be just the ticket. Yunghi Choi Epstein, of Lawson Carter Landscape Design in Washington, DC, says that clients with small spaces often say they can't plant trees. "But I tell them that you need trees to give scale. Trees automatically make the space seem bigger." The tree's canopy serves as the outdoor room's roof, providing a sense of shelter.

Epstein uses flowering pears and European hornbeams in a line to provide a visual screen in the narrow spaces that are so common with rectangular city lots. These narrow strips between the house and property line can provide a place where guests can step outdoors for a drink. In really tight situations, Epstein uses narrow shrubs, such as nandina, and vines against a good-looking fence.

Shirley Street, who works for the city of Falls Church, Virginia, designed a small park as a teaching garden to demonstrate plants and trees appropriate for small areas. Her demonstration garden has both natives and exotics. Using natives can be advantageous because many are less susceptible to disease, require less water, and resist harsh weather. But some landscape architects maintain that cities are highly artificial places where it is questionable whether native plants are well adapted to the harsh urban conditions.

When sunlight is desired for flowers and vegetables, a smaller tree such as an ornamental plum or a tree with less dense foliage, such as a honey locust, is a good choice. Douglas Wildman, director of design and construction for the San Francisco League of Urban Gardeners, notes that Bradford pears provide a vertical profile that allows light to reach the ground. They would be ideal, he says, for an alley surrounded by high-rise hotels in the city's Tenderloin district that is being transformed into a vestpocket park like those popular in New York City. (See "10 Don't-Miss Parks in the Big Apple" on pg. 32.)

Rooftop and vestpocket gardens can cost as little as a couple of hundred dollars. In residential situations, says one landscape architect, you can do a lot for $1,500. After that, the sky's the limit.

Greer Maneval points out that vest-pocket gardens can increase property values by as much as 10 percent. "An inviting mix of plants, walkways, and water features will enhance your property's curb appeal," she says, "giving you a real edge in the tight real estate market of the '90s. Plants are one of the few investments you'll ever make that will constantly be growing in value." No pun intended.

RELATED ARTICLE: ROOFTOP FAVORITES

Northeast

Little leaflinden Dogwood Flowering cherry

Mid-Atlantic

Hackberry Ginkgo purple-leaf plum

San Francisco Bay 

European olive New Zealand Christmas tree Holly oak

Pacific Northwest

English howthorne Leyland cypress 

Southwest

Soaptree yucca acacia (A. minuta)

RELATED ARTICLE: A GARDEN OF A DIFFERENT COLOR

In all the years I lived at the Richmond in Washington, DC, I never realized that its garden was constructed above an underground parking garage. Many pocket parks in urban areas are planted on top of garages. The challenges this kind of park presents are the same as those for rooftop gardens.

Maneval explains that the Richmond's garden is growing in three or four feet of soil atop a concrete slab, which is pitched like a peaked roof so that rain and irrigation water that seep through the soil drain off to the sides. Drain pickups in the structure connect with the building's drainage system.

"The keys to any rooftop plan are weight and water," says landscape architect Guy Morgan Williams, who has designed a number of rooftop gardens in Washington's historic Georgetown district. Williams notes that consulting an architect or structural engineer to determine the roofs weight-carrying capacity is essential.

Factors to consider are the combined weight of planting containers, soil, water, and plant material - including the increased mast of a tree when it's fully grown. Soil type and depth are another factor. Specially designed soil mixes may be required to reduce weight while providing nutrients. A commercial mixture of what is called "artificial soil" - which contains vermiculite or pearlite, humus, and other materials that allow the mixture to retain water while remaining lightweight - is preferable to heavy clay or light sand. The important thing is that the soil retains water but not to the point where plants become waterlogged. Metering devices to indicate moisture levels can be helpful and good drainage holes are essential. Plants need adequate soil depth for root space, and a rooftop garden must be designed with tree height in mind. Trees are typically planted on berms (mounds of soil) to achieve adequate depth.

Height restrictions are another factor. On an apartment balcony, the overhang of the unit upstairs may limit the size of the tree selected. And water is critical. A large garden will require some sort of irrigation system, and appropriate drainage will be needed so that you don't create a water problem for the building.

Climate is another factor. Trees and smaller plants on rooftops and balconies must withstand extreme heat from sunlight intensified by reflecting off the building. They may be required to survive strong wilds, particularly at the building's corners. If lightweight soil mixes are used to reduce the weight load, then the plants may be more vulnerable and stakes and gay wires may be needed. Finally, temperature extremes can be significant; you may have to use plants that are tolerant of expansio and contraction.

Urban trees are subjected to extreme stresses, but rooftop trees face even worse conditions. You may need to select species that are hardier then those normally planted in your temperature zone. Even so, their life spans will be reduced, so access to the rooftop for maintenance and replacement of plane material should be practical and safe. Frequent maintenance for insects is especially important, given the extra stresses. Bugs find plants - even when they are growing 10 stories above ground.

Williams advises avoiding trees that have invasive roots that may go through the waterproofing membranes used to line planting beds or containers. A metal liner may be the answer to prevent roots from following the water. Also, select slower-growing trees that require less frequent replacement.

Even though roof gardens are basically containers, they allow more space for roots to grow then pots do. Short life expectancy is the reason Mel Johnson, program director for San Francisco Friends of the Urban Forest in California, says he rarely plants trees in containers. He uses pots only where planting in the ground is simply nut feasible, such as places where basements or underground vaults extend beneath the sidewalk to the curb.

"Containers basically are caskets," he says. "Trees in them will choke to death, so you will have to do rotational planting (removal and replanting) us with any outer container. It's a totally artificial situation."

Whether creating a vestpocket park, a rooftop or backyard garden, or a terrace, success depends on researching these factors in your specific climate and planting location. - NORAH DEAKIN DAVIS 

NORAH DEAKIN DAVIS - former managing editor of AMERICAN FORESTS, writes on natural-resources issues from aboard her sailboat, Richmond Studio, moored in Washington, D.C.