Grand designs

Is it more difficult to make a garden on a virgin site, or to adapt an existing layout to your own taste? I've heard wild and anguished arguments on both sides. Those who are stuck with heftily laid paths going where they don't want them, dream of the wonders of a green-field site and the infinite possibilities that nothingness represents. Those who have nothing, long for a few features to pin a design on: a tree, a bit of wall, even a shed, if it can be covered in trellis and act as the focus of a viewpoint.

My greatest sympathies are with those who start with nothing, which is why I was so impressed with the work that the garden designer Cary Goode has carried out at her home, Thornhill Park, Stalbridge, in north Dorset. The 18th-century house sits cold, bare and exposed on the top of high ground, with views in all directions.

But you don't get views without also being exposed to wind, and this garden has little natural shelter. James Thornhill, Hogarth's father- in-law, who built the house in the 1720s, must have been some crazy kind of megalomaniac to choose such a position. Building at a time when "Capability" Brown's landscape movement was all the rage, he never got round to making a garden.

Well that doesn't sound like nothing to me, you may be muttering rebelliously. A Palladian villa, lovely views ... But if you go there, you are more aware of the problems to be overcome than the advantages of the situation.

When Cary Goode and her husband, Richard, moved into Thornhill Park three years ago, all she had to work with were a lawn, a field and a cedar tree. The formal house called for a formally designed garden, but Mrs Goode believes passionately that a garden should fit visually into the wider landscape. So the views presented difficulties in terms of the design. In this situation, the wider landscape could not be ignored. It dominates in every direction. Somehow she had to make buffer zones, so that the garden could seem to drift seamlessly over the boundaries into the fields beyond.

She's done this rather cleverly by tucking her excellent, colour-filled, mixed borders in places where, as you stand on the top terrace by the house, they don't distract from the wider scene. The ground falls to the west in a series of wide, grassy levels. When you stand in the wild garden, the farthest and lowest of the levels, you look back over banks of silver and gold plantings which are hidden from the house itself.

This is, of course, still a young garden: nascent yew hedges cower behind sheltering hazel hurdles, the nut walk and the hornbeam arbour are only the skeletal beginnings of the splendid features Mrs Goode hopes they will be in 20 years time. But that is why I found it interesting. You rarely get a chance to see a garden laid out on such an ambitious scale so early in its development. Mature gardens make design seem easy. Here you can feel the thinking.

Because you still seem close to the decision-making, you feel freer than in an established garden to disagree with some things. I would not have used the purple-leaved sycamore for the short, introductory avenue to the house. And I would not have made the narrow, well-planted alley (bergenia, box balls, viburnum) up the right-hand side of the formal garden on the north front of the house finish in a dead end. Blind alleys make me feel trapped. I would have made an escape through the adjoining rose garden.

The clay soil, says Mrs Goode, is "dire", but you'd scarcely know it from the lazy, settled look of the borders, where there are plenty of self-set seedlings jostling for space. I particularly liked the bit she calls the bishops' and cardinals' walk - deep, saturated purples and reds from tulips, tree peonies, masses of deep opium poppies, dark-leaved dahlias, honesty, spurge, the geranium `Johnston's Blue', lupins, the deep purple Geranium phaeum, angelica with heavy purple foliage, and Rosa rubrifolia.

Mrs Goode's biggest investment was in semi-mature trees to give at least an illusion of maturity to the garden. She found, against what one would have expected on this exposed site, that they settled and succeeded better than the younger trees she planted. But she remembered to water them well. That was the key.

The lines of the garden are drawn to reflect those of the house. The north side faces on to lawn, with a formal box parterre directly under the windows, and a rose garden at the far end - underplanted with pinks. A long, narrow hornbeam walk leads to a small, classical summerhouse and separates the lawn from the informal willow garden below.

Here, you'll find a kind of willow igloo, designed by Clare Wilks and made from seven different kinds of willow. Visitors are invited to weave it as they pass by. Mown paths through the long grass take you past masses of different willows: the violet willow, Salix daphnoides, with purple winter shoots, the hoary willow, S elaeagnos, with yellow autumn foliage, S x rubens `Basfordiana', with brilliant orange-yellow twigs.

The nut walk - walnuts and hazels - separates the garden to the north of the house from the more intricately planted areas moving out from the west front. The gravel and lavender hedges by the house are marked off by a low balustrade and a narrow iris border. The purple and white bearded iris `Dancer's Veil' was already in bloom when I was there.

A slightly gaunt orangery at right angles to the house provides a protected corner for yellow borders with variegated comfrey, giant euphorbias, potentilla, golden-leaved elder, hostas and yellow violas. From here, it's flowers all the way down to the boundary of the garden where a rough path leads into a stunning hazel coppice, carpeted with bluebells. As I said, problems, problems, problems ...

Thornhill Park, on the A357 1 mile south of Stalbridge, Dorset, is open Sundays (2pm-5pm) and Fridays (10am-5pm) until September. Admission pounds 2. Plants for sale.