The Saxifrage
What is an alpine? Theoretically, it is a plant which grows naturally above the tree line, the line above which no trees grow, and below the snow line, the line above which the snow never melts. Alpines can be found at altitudes as high as 19,000 feet in certain mountain ranges, but as low as sea level in the Arctic zones. In the European Alps they are generally found above 5,000 feet. But the conditions can vary so much. The soil types vary greatly according to rock type and historical formation. A soil which has developed from the limestone of the Dolomites is entirely different to the neutral or acid soil to be found in the Himalayas.
In the true alpine region the natural climate, depending on the altitude and location, often consists of very short growing seasons and extreme climatic conditions. Air temperatures fluctuate greatly. Sunny south-facing slopes are rapidly warmed by the sun's rays during the daytime and cool quickly at night. As a result, soil temperatures are often a few degrees warmer than the average air temperatures. Shady regions, such as north-facing crevices, can be considerably colder, and offer a home to an entirely different range of plants that are equally well suited to the exposed north-facing garden. At high altitudes rainfall decreases rapidly and during summer many plants only receive light mists. In the autumn snow arrives, air temperatures drop rapidly and plants are sealed in a clean, dry cocoon until the following spring, when the warm sun rapidly thaws the snow, flooding the plants and forcing them into growth. Many of them flower within a few days of emerging from the receding snow line.
A north facing mountain slope, open to the north winds, will be cold and relatively dry. In a valley protected from the winds and into which the shadow of the mountains always falls so that they get very little sunlight, will be cold and wet. Yet a slope facing the south which is bathed in sunlight from dawn to dusk when it is not cloudy will be warm and wet. Moderately level plateaux will have accumulated a depth of humus rich soil which will support a different plant community to rocky slopes with their screes and moraines. A soil-packed crevice on a south-facing cliff in the Dolomites is vastly different from the peat bogs of the tundra. A plant growing on an exposed rock face must be capable of surviving for months in temperatures which do not rise above freezing without the benefit of a protecting blanket of snow, and then suffer from hot sunlight reflecting from the bare rock, something that would desiccate any but the most specialised plant. Some plants are found in heavy clays and will have an almost continual supply of water, whilst others have to thrive on a well-drained, extremely gritty medium, which they can only do by having widely spreading root systems which tap the underground water to supply a very small amount of top growth. Others cling to rock faces and crevices, and are hardly ever soaked by rain or melting snow. Alpines have survived in the wild in these very hostile conditions for many hundreds of years by adapting themselves to these conditions. It is no wonder that the plants classified by the simple word 'alpine' have such varied appearance, and require such different climatic conditions if they are to survive. What is surprising is how many of these plants will adapt to the environment of an English garden.
All right, we do have to be prepared to put ourselves out a bit to grow some of them. An alpine house to keep the plants away from the vicissitudes of the English climate and provide the correct conditions - after all, a hairy or felted foliage which forms a barrier to the cold and sun on the dry upper slopes of a mountain traps moisture at wet, lower levels, and the plant can rot away. Maybe an alpine garden, a small area where the local soil conditions can be changed to suit the plants we want to grow without changing the climate. Or perhaps a rock garden to give a well-drained area for those plants which have deep roots. We may have to protect some of them from the rain and others from the cold winter winds. The growing of alpines is a fascinating way of bringing together plants from many areas of the world, and which will provide a wealth of colour for any garden, small or large, and for almost any aspect. The range of plants is very wide. Some, like saxifrages and sedums, are easy to grow and are suitable for the person just starting. Some offer labour-saving possibilities for those with not too much time to spend in the garden, while others supply a never ending challenge to those whose one desire is to encourage plants to survive and even flower in alien environments. There is something for everyone.
The best way to succeed in the growing of alpines is by copying, as closely as is practical, the soil and climatic conditions in which the plants grow normally. By doing this it is easy to establish many of the more common types without any difficulty; and is the only way to succeed with some of the rarer species. One of the hardest problems to solve is the one of light. The light spectrum in the mountain regions consists of more blue, violet and ultraviolet than is generally found in this country at lower altitudes. This problem is compounded by urban pollution, which significantly reduces light transmission and so restricts the growth of high-region alpines. This is the main reason why some of those plants which normally grow at the highest altitudes fail to prosper. Alpines have adapted their habit and shape according to the natural environment. If we are to grow them successfully, then we must adapt the growing conditions to suit their needs.
Happy gardening,
Bill Hutchings
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page last updated 6 FEBRUARY 2000