Like stamps, Alpines are small - they must be to survive mountain gales - and are often set out individually rather than in clusters. Collectors may try to mimic native conditions by building a rock garden to display their precious specimens; just as philatelists put stamps in an album.
Yet rock gardens often lead to disappointment. It is not just the stony crags that make Alpine slopes distinctive, but the altitude and snow. Grown too low, without their snug white winter covering, the plants can get straggly, contract diseases and lose their compactness. To prevent this, some enthusiasts keep them indoors, as at the Alpine house at Kew Gardens, where temperature and light levels can be controlled. Others find the process too false. They prefer to admire these exquisite specimens in their native habitat. Which is why more and more devotees are making the pilgrimage to the rocky heart of Europe - and why holiday companies are beginning to organise specialist tours for them.
Today's horticultural pilgrims are following in the steps of the intrepid Victorian plant hunters who loved to scour the mountain ranges of Europe and Asia, seeking new plants hardy enough to survive a British winter. As a result, Alpines made their first appearance in British gardens in the 1860s - many of them delicate, miniaturised versions of common lower- level plants, such as primulas, orchids, poppies and irises. Rock gardens, or rockeries, came into vogue at the same time, but have never been universally loved. In 1914, Reginald Farrer, a plant hunter and Alpine enthusiast, wrote scathingly: "Everyone must have their rock-work and the very rich are out to purchase the glories of the Alps at so much a yard - with all the more contentment if the price be heavy, so that their munificence may be the more admired."
Despite such withering scepticism, Alpine plants and rockeries grew in popularity. In 1921, the plant collector Arthur K Bulley acquired some ground on the slopes of Mount Snowdon and made an unsuccessful attempt to start an Alpine garden there. In 1929, the Alpine Garden society was formed and now has 13,500 members. A popular alternative to a rock garden today is a more manageable stone trough or tub.
Austria is a good place to visit real Alpine gardens. The country's highest was created by the University of Innsbruck in 1930 and opened as a public garden three years ago. Two thousand metres up Mount Patscherkofel, south of the city, the precipitous garden straddles the tree-line - the highest point of the mountain where trees can survive. Dr Armin Landmann, a senior botanist at the university, took me up in the cable-car that climbs to the peak. As we neared the top, we saw patches of red flowers beneath us. These are Alpine roses, a low-growing form of rhododendron, as prolific on these mountains as heather in Scotland: indeed they belong to the same family. It is easy to confuse them with the related creeping azaleas, the Alpine version of a favourite garden shrub. The flowers of the azalea are smaller and paler than the Alpine rose and they hug the ground more closely.
You enter the garden at the top of the slope, taking in the magnificent views to the south, and walk down towards the tree-line. Some of the plants, even this high, are familiar to lovers of British wild flowers - for instance lady's mantle (Alchemilla vulgaris). Dr Landmann, strong on the local folklore, recounts the legend that if a woman bathes in a solution of alchemilla she can regain her lost virginity. A more plausible tale surrounds the edelweiss, the small white flower widely associated with the Alps - partly on account of The Sound of Music - although it originated in central Asia. Because the flower is rare and may grow in inaccessible crevices, a young man who presents a woman with a bunch of edelweiss is said to be expressing his undying love.
Dr Landmann can also offer more scientific insights. As we looked down the south-facing slope, he pointed out that many characteristics of Alpine plants arise from their long period of snow cover every winter. The snow keeps out the worst of the frost and, more surprisingly, the damp. When it melts, it supplies a reserve of summer moisture, badly needed in the rocky, quick-draining environment. Many failures in growing Alpines at lower levels can be put down to the difficulty of replicating these conditions. Another error is to give them too rich a growing medium. Mountain soil is poor in nutrients, in better ground they get over-fed.
Alpine gardens are seldom a large-scale riot of colour. Instead, as we walked down the winding paths, pockets of bright, gem-like flowers caught the eye - the blue Alpine snowbell; the yellow bellflower, its flowers clustered round a central spike like a hyacinth; yellow and purple heartsease; globeflowers (a grand version of the common buttercup) clustering round a pond; and, shyest yet most desirable of all, the gentians, most in a brilliant shade of sky blue. Clear, bright colours are what attract Alpine enthusiasts.
The second garden I visited boasts a larger and more varied collection of Alpines. It is at the ski resort of Kitzbuhel about 100km from Innsbruck, and involves another cable-car ride to a height of nearly 2,000m to the top of Kitzbuheler Horn, overlooking the town. The garden has been created just below the summit and its setting looks more natural. In particular, gentians proliferate both in the beds and in the surrounding meadowlands. There are some imaginative plantings in the beds - for instance clusters of red moss campion (stone rose) cling to the base of a rock, while an Alpine clematis climbs alongside. A section near the top is devoted to plants originating in the Himalayas, such as the Nepalese geum, with yellow flowers like buttercups. Other bright spots are clumps of yellow helianthemum (the Alpine version of the cistus, or rock rose); many tiny species of thyme; and martagon lilies, known as Turk's cap for the shape of their dark pink flowers with rust-coloured spots.
While visitors might want to see at least one of these Austrian gardens, they will also get pleasure from walking the hills, spotting flowers in the wild. Guided walks are organised daily by the tourist office in Kitzbuhel and other resorts, and the guides are knowledgeable about the plants. Alpine roses proliferate, as do gentians, although they are often hiding in grass or behind foliage. Another common wild plant is the blueberry, delicious to pick and eat in late summer.
You do not have to be super-fit to walk the Alps. There are good, well- marked paths and plenty to see even on the lower slopes. If you don't want to climb all the way up, take a cable-car to the top or middle of a mountain and walk down. Don't dig up plants - it's illegal and they will not grow well in Britain. If your Austrian visit does give you the Alpine bug, then grow them from seed or buy plants from British growers.
Michael Leapman went to Austria as a guest of the Tirol Tourist Board and Crystal Holidays. Ring 01235 824324 for details of Crystal Holidays' Austrian programme
ALPINES BY POST
Many nurseries specialise in Alpines. Here is a selection of those that sell by mail order: Ashenden Nursery (01580 241792); Birch Farm Nursery (01342 810236); Bressingham Plant Centre (01379 687464); Charter House Hardy Plant Nursery (01387 720363); Posse Alpines (0116 2778237); Hedgerow Nursery (01535 606531); Thuya Alpine Nursery (01452 700548)
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