Gardens never stand still. Even young ones develop and alter from year to year. Plant growth and weather alone see to that, whatever a gardener might contribute.
But when a garden has evolved for centuries, it is bound to have undergone continual modification or even radical reinvention. New design fashions, the taste of different owners, access to plants, wealth (or the lack of it), are all factors that may contribute to the reshaping of very old gardens.
No wonder Callum Pirnie, head gardener at Crathes near Aberdeen, has history on his mind. He stands on the upper terrace surveying part of the three-century-old garden he manages.
To take in a comprehensive view of this compartmented garden, you must climb the spiral stairs in the 16th-century castle standing tall behind this terrace. Then, through a small high window you look out over an almost bewildering mix of the formal and the informal.
Crathes is an opulent tapestry of flowering shrubs and perennial plants rubbing shoulders. Lawns, old stone walls, yew hedges, and monumental topiaries are dominant features.
"There have been eight periods of development here," Mr. Pirnie says. "Layer upon layer."
In 1951, after 350 years of being owned by the same family, the castle, garden, and almost 600 acres of estate were made over by Sir James Burnett to the National Trust for Scotland.
Today, Crathes is a visitor attraction. But, more important, it represents "heritage." That label, not too difficult to pin onto a building, is trickier to attach to a garden. A living garden can't be treated as a museum artifact, frozen in time.
But how do you respect and conserve what remains of a garden's many layers of history? "It can never be the same as it was," Pirnie says.
He sees his task as restoring the garden "back to the essence" of what it was. He feels that in the 1980s "it lost direction a little bit" by losing touch somewhat with its past. But finding the "essence" is complex because "there isn't just one period to go back to." Three years ago an archeological survey showed the garden's development was less simple than previously realized.
When the trust took it over, the garden was seen as basically reflecting the interests of Sir James and his wife, Sybil. They had made it their own since 1926.
He collected trees and shrubs. She was a perennial plants enthusiast. Many of the trees and shrubs that Sir James added to his garden were from friends' plant-hunting expeditions. Shrubs from China, Chile, and Japan still flourish here, and they are increasingly seen as a valuable "genetic pool."
They have "a very, very good provenance," Pirnie says. "That's a big issue now in horticulture." So a major concern at Crathes today is conservation and propagation of rare plant material.
Lady Sybil was a hands-on designer. In some ways she shared a sense of natural style with still much-admired designer Gertrude Jekyll, but her intuitive sense of brightly contrasting color juxtapositions was surprisingly different from Jekyll's. Garden enthusiasts visiting Crathes get fresh ideas round every corner.
Lady Sybil left no written records about the garden. Fortunately for Pirnie, who is determined to be as faithful as possible to her style, Douglas McDonald, who was head gardener from her time until his retirement in 1982, is still here for advice.
The upper pool garden nearest the castle is a superb example of Lady Sybil's originality. There are intense contrast colors from June to September: purplish-bronze foliage, reds, yellows, oranges. All of this color seems sharpened by the intensity of light northeast Scotland is known for.
Plants with hot colors, however, present a problem at Crathes, because they can be too tender to stand the harsh winters that strike about once a decade not to mention the frequent cold winds and heavy snowfall. When plants are brought in from the warmer south of England, they often die.
Pirnie finds this another reason to respect the history, and the geography, of the place. "The old varieties Lady Burnett used are absolute crackers. They've been here 50-odd years," he says. "[They are] proven varieties that do well here." This is a lesson home gardeners are beginning to learn. Growing what will naturally thrive in your soil and climate is easier and more enjoyable than trying to force foreign exotics to grow in an unsuitable climate.
This is not to suggest that gardeners shouldn't experiment. Clearly, Sir James did. And Pirnie does. But Pirnie emphasizes that this is not "his garden." At the same time, it is also by no means just Sir James's and Lady Sybil's garden.
"There was an incredible garden already here, and a framework," he says.
The enormous topiaries go back at least to the first years of the 18th century. The hedges joining them were planted in the 19th century, when the upper areas were turned into geometrically formal pleasure gardens.
The second level features two gardens: One is a rose and lavender garden, the other is "the blue garden" with blue-flowered annuals in beds that are edged with clipped miniature box (known as boxwood in the United States) hedges. The lowest level is like a heaving sea of plants and shrubs, including a white border and a double border that predated Lady Sybil.
Another double border that is, however, pure Lady Sybil, is one that is scintillating in June each year. At one end stands a tiny dovecot. It emphasizes the cottage-garden character of her gardening.
The yew hedges are, Pirnie is certain, in need of attention. Their girth has expanded over the years and now makes the annual trim increasingly difficult. It also courts disaster from heavy snowfall.
Although the decision will be made by a committee, Pirnie believes the yew walk may have to be demolished and replanted. Already one hedge bordering the croquet lawn has been cut back more than six feet.
Some visitors who love Crathes object to such radical actions. But Pirnie's pointed question is: If something isn't done now, will there be any yew hedges surviving here at all in a hundred years?
Managers of historical gardens need to look back sensitively. They also have to look very boldly forward.