The kindest cut: The intricate Japanese art of niwaki is now more approachable, thanks to the skills of a former British sculptor. Anna Pavord reports.

We all think we know what a bonsai tree is. Translated literally, the word means no more than "cultivation in a tray". That, of course, is the least of it. The real point is to distil in miniature the essence of nature. Niwaki is a much less familiar term, but as Jake Hobson explains in an engrossing new book, Niwaki: Pruning, Training and Shaping Trees the Japanese Way, it has the same aim. The difference is one of scale. A niwaki is a garden tree, growing with its roots in the ground rather than in a tray. From now until the new year, teams of specialist pruners and clippers will be moving through Japanese gardens, enhancing the poise of junipers and maples, setting guy ropes to improve the angle of an azalea branch and, in the case of pines, stripping off all the old brown needles so that only the freshest, greenest foliage is left on the tree.

That's not a job you could ever expect to do on a wild pine, 60ft or more high. But as Jake Hobson demonstrates, niwaki developed as a way of keeping trees in gardens in proportion to their surroundings. The art lay in developing specific ways to constrain them while preserving the essence of each one's soul. The book is more than usually absorbing because Hobson trained as a sculptor before he ever got interested in gardens. He went to Japan immediately after graduating from the Slade School of Art and winning a travel scholarship to study the cultural phenomenon of the cherry blossom season and the effects it had on Japanese people.

The cherry blossom was good, but the thing he most remembered from the trip was the sculptural quality of the garden trees: Cryptomeria japonica in the suburbs of Osaka Prefecture, beautiful Ilex crenata in the grounds of a hospital in Hakone, Pinus densiflora outside the art museum in Shimane Prefecture. Within a year, he was back in Japan, teaching English and working in an Osaka nursery where various members of the Furukawa family started to teach him the philosophy of the niwaki in which the nursery specialised.

So he's approaching the subject with the eye of an artist and an appreciation of the culture that brought these staggeringly beautiful objects into Japanese gardens. But you can't prune or train trees without understanding how they grow, and his year at the Osaka nursery was followed up by another five years at Angus White's iconic nursery, Architectural Plants, near Horsham in Sussex. Then he set up a company importing tripod ladders and fine pruning tools from Japan. I've got a pair of his secateurs, but I only use them for best occasions. I want to maintain, for as long as possible, the feeling that to use them is a treat. They are light, precise and frighteningly sharp.

His book is practical, in the sense that through photographs and drawings he explains the differences between the various styles of niwaki: bendy, twin-trunked, multi-layered, with branches set out in alternating steps or with foliage clipped into shell-like domes. Succeeding chapters deal with the most important plants used for niwaki in Japan and show how to train them. Pines are top of the list. As he points out, the three native species are "loaded with cultural references". It is one of the most easily manipulated of all garden trees, allowing the tree growers and gardeners to speed up the maturing process that gives pines so much character.

By nature, Pinus thunbergii favours the rocky, windswept coastline of Japan. In a Japanese garden, rocks, gravel and ponds are used to evoke this natural environment and the tree trained to mimic the wind-sculpted forms found in the wild. In the west, our topiary tends to be symmetrical: cones, balls, pillars, cubes. Or else it's whimsical - peacocks, rabbits, battleships of lonicera. In Japanese niwaki, asymmetrical forms are thought to be more beautiful, odd numbers more satisfying aesthetically than evens. So where a tree produces branches at the same point either side of a trunk, one will often be shortened, or cut off altogether and the tree persuaded to adopt a shape that makes it seem much more ancient than it really is.

Some of the underlying aesthetic of the niwaki comes from the fact that Japan is a crowded country: 126 million people are crammed into a scattering of islands no more than about 900 miles long and rarely as much as a hundred miles wide. Living spaces are tiny, gardens even more minute. Garden trees have to be controlled to stay in scale and harmony with their surroundings. But Jake Hobson also points out that both Shinto and Buddhism have had an important influence on niwaki. They underpin the respect for nature that is at the heart of Japanese culture and which reinforces the desire to interpret nature in symbolic ways in their gardens, temples and parks.

We tend to use just one phrase - cloud pruned - to describe the Japanese specimens (often Ilex crenata) imported into this country and sold at eye-watering prices by specialist nurseries. They'll probably have rounded clumps of neat evergreen foliage balanced on short horizontal arms breaking from a single, central trunk. Ilex crenata is slow growing, so the proud new owners of these pieces (not me, worse luck) have only to keep within the lines, as it were. Like a child colouring in a picture, the shape has been predetermined.

But a Japanese gardener would be able to make one of these things from scratch and would also have a long-term vision of how each of the niwaki might change as it developed. That's a far more difficult skill to acquire, but Hobson tells you everything you need to know. Thinning, training and clipping are the key skills, but most important is an eye, like a sculptor's, which sees what can be released from a mass of greenery, in the way that an artist can see the form he needs to liberate from his block of stone.

Niwaki, whether made from Japanese natives or British ones (there's no reason why we can't borrow the technique) are by their very nature perfectly adapted to town gardens. It's surely a far more appropriate and achievable way of bringing nature into the urban jungle than meadow gardening, the present obsession. Unfortunately, even the clever Japanese have found no way to make Leyland cypress beautiful, but if you've a podocarpus or a cryptomeria, start thinning now.

'Niwaki: Pruning, Training and Shaping Trees the Japanese Way' by Jake Hobson, is published by Timber Press, 25. For a catalogue of Japanese tripod ladders and fine pruning tools suitable for creating niwaki, send an SAE to Jake Hobson at Harvard Farm, Halstock, via Yeovil, Somerset BA22 9SZ, 01935 891825, www.niwaki.com. Jake Hobson will be demonstrating niwaki techniques this Thursday (10.30am-3.30pm) at the English Gardening School at the Chelsea Physic Garden in London, cost 125. For more details call the EGS on 020-7352 4347, or visit the website, www.englishgardeningschool.co.uk