History grows here: prune with care

The National Trust, which celebrates its centenary this year, had already been around for 50 years before it began to think of saving gardens as well as buildings and landscapes. But last year, more than four million people visited Trust gardens a nd they always take the lion's share in any list of the Trust's most visited properties.

The two most popular are not Sissinghurst and Hidcote, darlings of the style brigade. They are Studley Royal in north Yorkshire, acquired by the Trust in 1983, and Henry Hoare's 18th-century masterpiece, Stourhead in Wiltshire. Taken together, the Trust'

s 162 gardens cover nearly 400 years of garden making. In them grow the world's largest and most diverse collection of cultivated plants.

But what are these gardens for? Are they exercises in nostalgia: first cousins to theme parks, recreating the settings of a vanished way of life for us, the tourists, to wallow in? Are they museums: chronological chapters in a book of garden history? Arethey botanical holding pens, providing the widest possible range of growing conditions in which rare plants can thrive?

Are they just nice little earners? Though the philosophy of the founders of the Trust - Hunter, Hill and Rawnsley - was based on protecting and giving access to land, there is no turnstile at the entrance to a footpath. The Trust's own figures show that gardens, more than any other type of property, attract visitors who pay, as distinct from members who do not.

You can trace the painful birth of a policy for gardens in a series of large files in the Trust's archive. The handwritten index of the first volume gives a taste of the matters under discussion: an appeals organiser for the Gardens Fund, a broadcast by Vita Sackville-West for the same purpose, an interview with the Chancellor of the Exchequer about tax exemption for historic gardens (an issue which is still unresolved). The idea of garden tours tailored for American visitors was first mooted, the desirability of an apprentice scheme for gardeners first voiced. The question of labels - green plastic or grey zinc - was debated at length. Nowhere in this neat index do questions of taste, design or historic content appear. The commi ttee members were primarily concerned with the practical aspects of the Trust's gardens. They worried about keeping paths swept, edges trimmed, borders staked. Nobody seemed to care about recording. Although it was standard practice to make minute invent ories of houses, downto the last teaspoon, no such inventories were made of the Trust's gardens. No plans of planting schemes or lists of key plants were drawn up. The idea of a garden as a historic document had not yet taken root.

Hidcote, the Trust's first garden, was created entirely within the first 40 years of this century by the American, Lawrence Johnston. But when he died in 1948, the Trust spread his collection of Regency garden furniture round other more "historic" properties. In just one year, the colour of the paintwork at Hidcote was radically changed, the camellia shelter was demolished, cedars on the lawn were replaced by ilex and vulgar `Kanzan' cherries were removed from the area called Mrs Winthrop's garden. TheTrust is now more careful that the values of one generation do not prejudice the possibilities of the next.

It was some time before the Trust addressed the tricky problem of "correctness" in gardens, either by full blooded restoration as at Westbury Court in Gloucestershire, or by adjusting the balance of features from different periods. But where do you stop the clock? A single garden may have had at least half a dozen major refits. Sometimes a kind of double bluff is at work, as at Montacute, where although the garden pavilions are contemporary with the 1588 house, the garden itself is a late Victorian pastiche of the 16th-century style. Adjustments depend on the prevailing criteria of worth. In the Trust this has generally meant preferring the 18th century to any other.

The first tentative steps in rewriting history happened at Stourhead where the garden had been laid out in the 18th century to represent an English version of Arcadia, a supposedly natural landscape which was in fact manipulated down to the last blade ofgrass. Brenda Colvin, the eminent landscape designer, who died in 1981, started the Stourhead correctness debate with a letter to the Times in 1960. She criticised the rhododendrons planted by its owner, Sir Henry Hoare, in the rhododendron boom years of the Twenties and Thirties. Graham Stuart Thomas, the Trust's first gardens advisor, agreed with her. The offending scarlet and pink rhododendrons were shifted from their prominent positions by the lake deep into the woodland.

An appreciation of the 18th-century landscape style has long been a mark of refinement among garden historians. But a straw poll, taken of Stourhead's visitors at its busiest season in April and May, would surely reveal that more had come to enjoy the rhododendrons than ponder on Virgil. The sixth baronet's plantings at Stourhead were a valid part of the garden's history.

These days there is a far greater understanding at the Trust that a garden is a living, developing amalgam of past fashions, styles and gardening activities. There is also a clearer understanding of the process of change. Change in gardens is inevitable - plants die, trees blow over - but replanting has to be driven by a sure strategy. Research often provides the answers. Where it does not, the Trust has to rely on more amorphous principles: "in keeping with", "in sympathy with", "historic pr ecedent". The burgeoning confidence of the present team of garden advisors shows in the exuberant Edwardian parterre at Kingston Lacey and the flower garden at Calke, neither scheme remotely in tune with present standards of good taste. And a good thing, too.

In terms of visitor numbers, gardens have become one of the National Trust's biggest success stories. As access is one of the key principles in the philosophy of the Trust, this is a good thing. But preservation is the other great precept. In gardens - as elsewhere in the Trust - the two tenets are sometimes at odds. This is not just a matter of physical damage. Mood, atmosphere can be destroyed, too.

For the Trust, which over the last nine years has doubled its membership to two million, access is likely to provide the biggest headache of the next hundred years. But as I gaze out over the immaculate planting of Powis's tumbling terraces, or potter ona misty September morning by the lake at Stourhead, I can't say I worry about it too much. I just say "Thank Heavens for Octavia Hill".

p Stourhead, Stourton, Warminster, Wiltshire is open daily (8am-sunset); admission £3.20. Studley Royal (and Fountains Abbey) at Fountains, Ripon, North Yorkshire is open daily (10am- 5pm) although closed on Fridays during January; £4. Westbury Court, Westbury on Severn, Gloucestershire, is open during the winter months by appointment only (0452 760461). Montacute park and gardens are open daily except Tuesday (11.30am-5.30pm); £2.60. Hidcote and Powis Castle, Kingston Lacey and Calke reopen at the beginning of April.