What is an alpine?
The mountain is a complex ecosystem that comprises successive zones of vegetation that vary according to several factors among which the most important is altitude. The hiker going up a mountain will note changes in the composition of the forest until, beyond a certain altitude, it altogether disappears . This is where the alpine zone starts, an environment where only herbaceous plants remain accompanied with low and twisted forms of shrubs.
Where trees are absent and air rarefied, plants are exposed to strong light, intense ultraviolet and harsh climate. Those that manage to prosper in this kind of setting are what we call alpines. They are different from most other plants from the fact that they are adapted to deal with extreme conditions that prevail in the high mountains. In fact, in order to insure survival of the species and produce sufficient seeds, they complete their vital reproductive cycle quickly within the short growing season that prevails at high altitudes, summer only lasting a few weeks in extreme situations. One thus observes plants that have particular features such as early and abundant blooms that are often brightly coloured and oversized in order to attract pollinating insects. Roots also take on special dimensions, they not only must insure solid anchoring to slopes and unstable mountain screes but also have to act as storage organs to provide the plant with enough energy that will allow for a vigorous early start when spring is back.
To optimally benefit from the few degrees of heat that are present at ground level in the high mountain, plants have adapted to grow close to the soil, forming carpets or growing with prostrate habits. Some species have gone around this problem by displaying dense hair cover on their leaves and stems while others have developed thick waxy cuticles , in both cases to prevent sharp changes in the unpredictable high altitude climate.
With such an insight into the alpine world, one might think that gardeners wishing to grow them need some skills in order to succeed. In fact several species are difficult to grow or next to impossible as the growing conditions they require are too specialized . The growing conditions our gardens present are quite different from those met in natural habitat, and more so in the mountains. Nevertheless numerous species are adaptable , that is they are possible to grow if one is ready to study them and find out about their life conditions in their natural habitats and then adjust garden conditions accordingly. To provide minimal favourable growing conditions and begin the exploration of the world of alpines , one has to namely amend soil to improve drainage, find a suitable site that is well lit, where trees roots are distant and weeds have been carefully eliminated as alpines are poor competitors and would otherwise easily abandon. An important item one cannot overlook is the use of rocks. It is an absolute must with this kind of plants, their survival being closely linked to the presence of rocks around them as it is an integral part of their environment.
What is a rock garden plant?
Rock garden plants are closely related to alpines ,being morphologically similar, yet they do not originate from the high mountain environment. They naturally occur below the alpine zone, in that lower ecological zone where trees are present. The plant diversity of what is known as the subalpine zone is greater, comprising a higher number of species. Soils are more developed and generally richer which ,together with a milder climate, allow to sustain such a high diversity.
For the rock gardener, these plants are more easily adapted to the garden since it is relatively easier to replicate the life conditions of the subalpine zone as opposed to those of the neighbouring alpine zone . In fact, plants that are found in nurseries sold as rock garden plants are often originated from subalpine environments and lower. Nurseries have more ease producing them, and when transplanted to conventional gardens they will generally not be faced with a fatal transplanting shock. Nevertheless one must be reminded of the close origins and similarities between alpines and rock garden plants while planning soil amendments in order to carry out proper preparation of the site because, although rock garden plants are known to be more adaptable, they will not tolerate waterlogged and heavy soils nor will they compete with tree roots and weeds very well.
Besides, one will note that rock garden plants generally take on creeping habits and often show restricted dimensions that are naturally associated with slow growth, characters that are common to alpines. A trait that is commonly used to help gardeners make their selection is height. Although by no means an absolute rule, it is often agreed that one should select plants and limit heights between 30 to 60 cm when wishing to stay in line with the rock garden theme. As with alpines, rock garden plants will be better harmonise and prosper in gardens where rocks predominate. In fact, the spaces under these rocks make up a sought after refuge to the roots of those plants as they keep uniformly cool and moist through the season, allowing rock garden plants to get by despite hot spells and other temperature extremes.