Yew and me: Anna Pavord visits a garden near Leeds where topiary is a cut above the usual

In the garden of Hillbark, Bardsey, just north of Leeds is one of the strangest pieces of yew topiary you're ever likely to see. Tim Gittins and Malcolm Simm have been gardening at Hillbark for 26 years, starting from scratch on a long, thin piece of ground that sloped away from the house to a stream in the valley below. Cleverly, they terraced the garden into three different levels and made a very beautiful pond at the bottom.

Malcolm can have had no idea when he first planted his yew tree that it was going to become such a dominant feature. Imagine an evergreen sunburst, each ray very long and thin, and each one a separate branch, bowing out from the same centre point. Every two years Malcolm trims the branches, clipping the greenery tight back. I wondered how on earth he managed the work, since the branches are as narrow as spider legs, but not stable enough to hold the weight of a ladder. "A bucket of bricks," he explained. He throws a rope over the branch he wants to work on, and then hauls up the bucket. Its weight pulls the branch down to a level he can reach. When he releases the branch, it immediately springs back up to its original position.

Malcolm is a potter and has spent most of his working life teaching art, so perhaps it's not surprising that the Hillbark garden has a lot of plants that are clipped and shaped to provide pieces of living sculpture. I particularly liked his family of box onions sitting in a circle, wearing crowns woven from willow stems. In a garden as crowded with incident as this one is, the evergreen topiary provides very necessary bulk and structure.

With homemade topiary, you are either building up a shape, as a potter does with clay, or releasing one, as a sculptor does with a block of stone. We've tried both methods, in yew and in box. Box is easier because it is more malleable, but yew makes bigger, bulkier eye-catchers. In our last garden, we took on a scraggy yew tree, and over a period of six years, tried to sculpt it into a piece of topiary.

The tree was about 8m (25ft) high and each year we took off a couple of its lower branches, working our way gradually up the trunk. It responded enthusiastically by sprouting new greenery all the way up and after four years, I gave it its first clip. A cone was the most natural shape to work towards, but for a while we had a weird hybrid: topiary with a tree sprouting out of the top.

It stayed like that for months while we thought how we might finish off our creation. The simplest option would have been to stick to a plain cone. Then we could have cut off the tree top quite low down the trunk, so that later we could clip the new growth into a neat point, without the bulk of the trunk getting in the way. But I fancied something a bit madder and waited for the tree to suggest its destiny. A cone with a ball balanced on top? A cone wearing a broad-brimmed Ascot hat? Then we left that garden and the yew tree still haunts me. Unfinished business.

Yew has a reputation for being slow, but when you cut it hard back, fresh green shoots grow with surprising vigour. Box is the only other tree that will respond to this draconian treatment (but not as reliably). It's why they both make such good hedges and why nothing matches them for topiary. Both give a sense of permanence to a garden, not just because they are evergreen, but because they are long-lived. Yews are difficult to date, but tree-expert, the late Alan Mitchell, reckoned that many churchyard yews, such as the one at Coldwaltham, near Pulborough in Sussex, were as much as 3,000 years old.

Because they don't erupt into mad blossom, or do flashy things in autumn, you underestimate them. You tend to take for granted, too, the way that a yew backdrop sets off more ostentatious features in a garden. They are tolerant of a wide range of soils and growing conditions. Like spotty laurel, they will put up with the challengingly dry growing conditions of city gardens.

Trees (and hedges), though, are more likely to respond well to hard pruning when they are in good heart. If you have yew you want to cut back – either a tree or a hedge – feed and water it well for a year before you start work. Though now is the time to clip box and yew, severe cutting (stumping back, it's generally called) is best done in April. Don't be tempted to leave bits of branch and twig sticking out. The best regrowth will come directly from the main trunk. If you are trying to reduce the width of a hedge, do one side at a time.

The top of an old yew hedge can become a frizz of twiggy growth, all of which can be taken out, if necessary. Top growth usually bounces back much more quickly than side growth. Feed (blood and bone is good) and water hedges after any drastic cutting back and mulch during autumn or winter with muck or compost. Yew, unlike Leyland cypress, only needs one clip a year and you can fit that in any time between now and late summer. If you clip too late, frost may burn off all the soft new growth, leaving it an unsightly brown.

I wish I felt equal to making a peacock in our new garden, but I don't. True topiarists are born, not made and I don't think I've got a peacock in me. I'd be able to look after one, if I inherited one, but sculpting one from scratch is a different matter. The best are those that sit, bulging massively in small cottage gardens, where they dwarf everything else around. There's a good one in a front garden at Queen Camel in Somerset. Sadly, they are fast disappearing, along with the people who created them.

If you want young yews to grow on into topiary pieces, you can raise plants from seed, sown in October. The seed is buried in the middle of the red berry, elegantly known round here as snot-gobbles. The red bit isn't poisonous, but the seed would be, if our stomachs could ever get round to digesting it. Fortunately, it isn't designed to be digested. It's made to shoot right through a bird's gut and out the other side, ejected with the added benefit of the dropping which will help it to germinate and grow.

Sow the seeds in a pot of John Innes compost and leave them outside. When the seedlings are a few inches high, line them out in a row and grow them on for two or three years before setting them in their final positions. Then you can start to clip.

If you want plants for a hedge, you should take cuttings from an established plant, so that all the plants will match each other. Seed-raised plants will all be slightly different. Take 7-10cm (3-4in) long cuttings of side shoots with a heel in September or October. Line out the cuttings in a narrow trench which you have lightened with plenty of sand. When they have rooted and are starting to grow away, transplant the cuttings into fresh ground at wider spacings and grow them on until they are about 45cm (18in) high. You'll then have the makings of a fine hedge.

The garden at Hillbark, Church Lane, Bardsey, nr Leeds, is open tomorrow and 10 July (11am-5pm), admission £3.50. For more information go to hillbark.co.uk