There are more than 1,000 community gardens in the city, which have evolved on the most unlikely sites - the Liz Christy Garden (named in memory of one of the group's founders) at the busy intersection of Houston and Bowery. The gardening equivalent of the fishes and loaves story - and every bit as much of a miracle - it has been transformed from an abandoned 50 by 150ft lot, littered with rubble, into a haven of flowers, vegetables, grape vines, and trees. There's even a pond - with frog - and a working beehive.
"It's the garden as a community centre," says Tietz. "When there's green it keeps people in the neighbourhood which makes it safer and acts as a catalyst for other self-help endeavours. When people get together and build a garden they realise they can do other things by community."
According to Dr Michael E Soule, writing in Biophilia Hypothesis, solitary communing with nature is just as important. "Our little acts of biophilia - buying bird seed, caring for pets, nurturing our gardens - sustain us emotionally," he writes.
The significant thing is that nature is responsive. One of the most terrifying aspects of the future world envisioned in Blade Runner is the rarity of real nature - never mind that androids have emotions and fake snakes and owls are indistinguishable from the real thing. Fakes don't need and don't respond to human care and it is that, as much as anything, that makes the non- organic urban landscape seem unsympathetic to humans. Perhaps therein lies the extra pleasure we take in the little oases of flora and fauna - all the more extraordinary for being so hard won - which are sprouting up all over New York.
"People have been making gardens with potted shrubs and rectangles of Astroturf on the roofs across the street," says New York illustrator Guy Billout, who was inspired by the view from the windows of his Lafayette Street studio in one of his illustrations for The Atlantic Monthly. Branches of trees speak surrealistically from the tops of buildings all over the city and the Rockefeller Center, between Fifth and Seventh Avenues and 47th and 51st Streets, has several roof-gardens. Sadly, they are not accessible to the public, but are visible from the eighth floor cafe of the department store Saks Fifth Avenue, and from the windows of those who work in the buildings nearby. "They are exquisite," says one local office worker. "But I've never actually seen anyone walking in them."
Those stuck at ground level can find solace in the pretty Channel Gardens (so-called because they are located between the French and English buildings of the Rockefeller Center) which lead to the skating rink. But if only a roof-garden will do, the sculpture roof-garden at the Metropolitan Museum of Art is lovely on a balmy day - and if it's raining there's the spectacular indoor garden in the museum's American Wing, which even has trees. There is also the exquisite little Greenacre Park, on East 51st and Second, which is often quiet and, in the summer, the Museum of Modern Art, on West 53rd Street, holds free classical music concerts in the museum's garden.
However, perhaps the most gorgeous public gardens in New York are those at the Cloisters, a branch of the Metropolitan Museum of Art, and a gift of John D Rockefeller - clearly a man who appreciated the value of gardens. The setting, Fort Tyron Park in northern Manhattan, couldn't be less urban. Coming out of the 190th Street subway station into the middle of nowhere is surprising enough, but arriving at the Cloisters building nearby is like stumbling into a time warp. Opened in 1938, the building incorporates architectural elements imported from the monasteries and chapels of 12th- and 13th-century Europe, and is the exquisite setting for several medieval- inspired gardens and courtyards. The most beautiful is probably the sweet- smelling Bonnefont Cloister Herb Garden - a tiny open courtyard enclosed by a high building wall on one side, a medieval cloistered walkway, with gothic arches on another and by two low walls overlooking the tree tops of the park below.
It is laid out like a typical medieval monastery garden. Raised beds contain a variety of plants and herbs that would have grown in the Middle Ages - including meadow-sweet, boxwood, marjoram, bryony, rosemary, periwinkle, oxlip, thyme, and sage. Arranged around a central well head are four beautiful quince trees, laden with fruit, which look exquisite against the pale gold walls and Gothic arches behind them. The few people who are wandering around look oddly anachronistic in their Nineties garb. Shakespeare's Beatrice and Benedick would be much more in keeping. "It is very romantic," agrees Jose Ortiz, assistant manager of the Cloisters. "People are always calling to ask if they can hold their wedding here. We say no, but people sneak in and do them anyway. I've seen them slipping rings onto each other's fingers." It is winter and on a day like today it is uncharacteristically deserted. "On Mondays when we're closed to visitors it often feels like mine," says horticulturist Susan Moody, speaking for all the gardeners. However, they also love having visitors and sharing information about plants and seed sources with the public.
A huge bite which has been taken out of one of the pear-like quinces still in the tree is viewed with some disapproval and I am reminded of the Garden of Eden - from which it was Man's first punishment to be expelled.
Punishment indeed when one considers a recent study of Reading University's Department of Horticulture, which found that even being able to see green has "a powerful preventative and curative influence on health". Maybe, as Wilson believes, the days when humans depended on nature for their survival has given us a genetically-based emotional need to affiliate with the natural world. Or perhaps it is nature's enduring ability to regenerate itself that inspires us. Whatever the reason, the gardens of New York, and perhaps this one especially, offer restorative respite from the harsh concrete world of Manhattan. In the words of the poet Dorothy Frances Guerny, with "the kiss of the sun for pardon, the song of the birds for mirth, one is nearer God's heart in a garden than anywhere else on earth." !