Although the Big Apple prides itself in all avenues of the offbeat, Michael Riley is quite possibly one of a kind. He tends ferns, begonias, and orchids in his apartment on the Upper West Side, but you'll find few potted plants there. Michael's collection scales two cork bark-covered walls, floor to ceiling, a living wallpaper for this urban gardener. Aroids and orchids cling to the cork bark. Gesneriads nestle in pockets Michael carves in it. Bromeliads hang from threads. Potted colocasias and maidenhair ferns ring a pair of ponds sunk in the tile floor. If Tarzan suddenly swung through, beating his chest and bellowing, his appearance would seem absolutely apropos.

A cue from nature
Long before the advent of his living wall, Michael Riley accompanied a scientific expedition to Ecuador, one of the most botanically rich countries in the world, to make herbarium specimens and collect seeds for horticultural institutions. There he received a generous dose of botany without bounds. "The rain forests and cloud forests gave me a whole new perspective," he says. (That understanding was the only souvenir from the trip-the explorers weren't permitted to bring home live plants.) "First of all, there were no plant labels there," he explains. "I had to start analyzing what I saw. I looked for flowers; I noticed how things grew. And they grew on sides of trees, on sheer solid clay cliffs. It opened up a vast new world of how plants coexist." He realized that certain plants do not need the pots to which they are often confined in culture-in fact, they can do better outside of them. His curiosity would soon evolve into an intense hobby.

When Michael moved to New York City, he pacified his need for nature by growing semperflorens begonias beneath the fluorescent lights in his first apartment's kitchen. He spent seven years in a brownstone with an outdoor garden. Finally, he bought a building with a defunct restaurant on its ground floor, a loftlike, open space, on the Upper West Side. In the 25 years since, he has made the former eatery his home-and his garden.

The living walls
Michael's apartment is a carefully choreographed ecosystem that relies on cork bark, artificial and natural light, and overhead sprinklers. Two in-floor pools provide extra humidity. The tile floor makes watering, with its inevitable spills and drips, stress free.

The collection emphasizes foliage over flowers. This reflects what Michael saw in the cloud forests of Ecuador. There he learned to value leaf texture, venation, and shape. The display does bloom-gesneriads and orchids furnish a fair share of showy flowers. But a steady supply of shiny, corrugated, wavy, and otherwise riveting leaves remains the focus.

The walls paint a portrait of fascinating botanical relationships. How these plants grow and interact particularly interests Michael. The majority of his plants are epiphytes, plants that derive moisture and nutrients from the air. The cork bark on which they are mounted provides nothing more than physical support.

Originally, Michael created little pockets in the cork bark to hold the plants. The plants found even these loose accommodations constricting and moved out, sending crawling roots over the cork bark. Now, Michael attaches new plants to the wall with sphagnum moss. From there, roots meander everywhere, much to his delight. If a piece of a plant breaks off, it will likely take hold and establish roots, thanks to the high level of humidity. Seeds also sprout impromptu. "It takes on a life of its own," Michael observes of his display.

Of course, he also gardens. He feeds the plants weekly, spraying diluted fertilizer on the foliage and roots. Although he's partial to the "natural look," he grooms and removes unsightly foliage. He leaves seedpods in place. Constrained somewhat by the parameters of the city environment, Michael focuses on moderate- to warm-climate plants; cool-climate growers would not be comfortable. In winter, he varies the temperature between 60° and 74°F. He says that keeping the apartment 74°F in summer proves more difficult than maintaining the heat in winter. "Yes, I go on vacation and leave the air conditioner running for the plants," he confesses.

As for watering, that's where Francisco Correa, Michael's partner, comes in. He waters the wall by hand, spraying the plants every other day if need be. "He talks to them in their native Spanish," Michael adds. "Which is what, he says, makes them bloom." Indeed, these plants feel at home on many levels here.

Recreating the rain forest
Ask Michael Riley how to create a horticultural habitat similar to the one in his New York City apartment, and he'll start simple: "First, you buy the building." No landlord is going to permit you to strip down their walls, install sprinklers, and rig complex lighting systems. The rest of his steps are similarly straightforward.

He began by stripping the wall down to brick. He added new studs and insulation, then applied external plywood sheathing to the walls. He stapled bitumen roofing to this layer for protection against moisture. Then he bought bales of natural cork bark (imported from Portugal but reasonably priced at one dollar per square foot) and affixed that with stainless steel plasterboard screws. Except for some minor deterioration from the dampness, the cork bark has held up valiantly. Excess water drains into a trough running along the foot of the wall, and spills are easily mopped from the tile floor.

Michael next tackled the plants' demands for high light and humidity. The south- and east-facing windows provide good sun. He supplements this with a high intensity discharge (HID) lamp and four fluorescent lights, each eight feet long, attached to the ceiling. These are set on a 12-hour cycle. He has recently installed two color-balanced incandescent lights as well. The room has a nine-foot-high ceiling, but the lights' beams only reach three feet down. Michael arranges the display accordingly, with shade lovers sited lower on the wall. The temperature also varies 10°F from top to bottom; an oscillating fan keeps the air moving. The plants are hand-watered several times a week. A sprinkler system in the ceiling and a pair of pools in the floor supply extra moisture and humidity.

What is an epiphyte?
An epiphyte is a plant that derives its moisture and nutrients from the atmosphere. In the wild, these plants usually grow on tree trunks, tree branches, or rocks. Many epiphytes are native to rain forests, where the frequent rains and humid air allow them to easily absorb plenty of water. They are also typical of cloud forests (rain forests at high elevations). Cloud forests are frequently immersed in low clouds, creating a cool atmosphere with 100 percent relative humidity. Although epiphytes live on trees, they do not take anything away from them. The host plant is simply a perch for an epiphyte.

Epiphytes have evolved special features to allow them to survive "unplanted." Many have a pronouncedly cupped shape; water and debris collects in the center of the cup, for the plant's use. Others are able to trap dust particles in tiny scales on their leaves and absorb nutrients from these. Epiphytes are not without roots, though they do not rely on them in the usual way. Some, such as some Tillandsia species, have "holdfast roots,' which only serve to fasten them to their host. Other epiphytes' roots primarily serve as anchors but also have the ability to take water and nutrients from soil if the plant happens to land in some.

Familiar epiphytes include staghorn fern (Platycerium bifurcatum); Dendrobium and Phalaenopsis orchids, certain bromeliads, including the urn plant (Aechmea fasciata); and certain cacti, including orchid cacti (Epiphyllum), Christmas cacti (Schlumbergera), and Rhipsalis.