How a tropical garden flourishes in Scotland

The Scots describe it as an oasis. And it is. You leave the Highlands, often forbidding in appearance when the heather is not out, drive through several miles of treeless peat bogs and rocks, and then run into one of the more beautiful gardens you will find anywhere.

It is, however, far more than the visual contrast that makes these Inverewe acres so remarkable.

Draw a line east from here on any map of the world, and it runs just south of Lenningrad in the Soviet Union. Drawn to the west, it would pass through Labrador, where the permafrost is never far away, and Hudson Bay, locked in six feet of ice for many months of the year.

And yet here in this northwest corner of Scotland, on the same icy latitude, Caribbean palms sway in the breeze and eucalyptus trees grow as readily as in the Australian outback. Bananas flourish.

A variety of plants grow unprotected here that can only be grown under glass in London's Kew Gardens hundreds of miles to the south.

The Gulf Stream, which makes it all possible, steers a consistent stream of moist tropical air onto this corner of Scotland, while a protective mountain ring prevents the advance of cold air from the interior. Winters are mild, and frost is as rare here as it is in Miami.

Yet little more than a century ago, Am Ploc Ard (The High Lump), as this section of the Wester Ross was called in Gaelic, was just that - a barren blob of a hill, its only tree a stunted, dwarf willow.

Down the centuries, the Lairds of Gairloch left it to the sheep until one of their descendants, a visionary by the name of Osgood McKenzie, recognized the potential. In a few decades he turned the garden from a theoretical possibility into practical reality.

What had kept this subtropical niche of Scotland largely barren for so long was its lack of protection from storms that bear down on the region each winter. Temperate it might be, but calm it is not when the North Sea is raging. One night last winter, for example, the garden took a battering from winds that clocked 110 miles an hour, but there was little to indicate that long, rough night when I walked through the garden recently.

Mr. McKenzie's windbreaks had come through yet another test.

In 1862, when he inherited Am Ploc Ard, McKenzie realized the land could be tamed if the wind could be cushioned. He began by building a deer and rabbit fence across the penninsula, then he planted a thick stand of Scottish firs and Corsican pines, backed up by thick hedges.

Rock was hauled away and soil brought in. Some 15 years later, when the trees were fully established, the gale that hit the windbreak on the shoreline came through on the garden side as not much more than a stiff breeze. Not only did the windbreak reduce wind strength, but it also dissipated the force of the driving rains (60 inches a year falls on this corner of Scotland) that had previously eroded anything resembling good soil as quickly as it was formed.

The windbreak established, trees from more temperate climes were brought in - eucalyptus, palms, California redwoods, and many others, even a New Zealand cabbage tree. One large Douglas fir was grown from a seedling sent to Inverewe by ordinary letter post from the US a century ago.

Something or other blooms in the garden every month from early spring to late fall, but most color is reserved for the summer months. Vegetables thrive in the Walled Garden, where there are some outstanding examples of espaliered fruit trees are on display.

The lessons for the home gardener here at Inverewe are many, but the principal one, perhaps, is what can be done when climate is modified and improved through wind protection.

Inverewe boasts an exceptional ''mini-climate'' for its latitude. Your backyard equivalent of Inverewe may come in the form of several ''micro-climates ,'' which you can bring about with plantings of hardy evergreens. When a garden area is sheltered from prevailing winter winds, but is open to the southern sun, plants from warmer climes can frequently feel right at home.

If you are interested in visiting Inverewe and some of the other subtropical gardens in this area of Scotland, write to: The National Trust for Scotland, 5 Charlotte Square, Edinburgh EH2 4DU, Scotland.