The rock garden, in its most common sense, is often confused with the alpine garden which is instead much more specialized.
In Italy, it often takes on another form, peculiar to the coasts: that is, it is the solution to extremely steep soils near the sea.
In the two cases the plants used will obviously be very different from each other: alpine or mountain plants in the first case; plants and shrubs characteristic of the Mediterranean maquis, generally united with succulents, in the other.
There may still be another solution, particularly for those who wish to have a rock garden in the plains, where it is very difficult to grow the mountain vegetation: it consists of using instead of those normally used, perennial or bulbous herbaceous plants, small shrubby evergreens that form, so to speak, the backbone of the garden.
However, the system for the construction of the rock garden will always be the same, with the difference that in the case of completely steep terrain there can be no choice on the position in which to erect it, except for some amendments, while in flat or moderately wavy extensions, it can be built wherever it is deemed necessary or preferable.
The most important condition for the plant will be that of a perfect drainage; therefore the existence of a slope will greatly facilitate the work, naturally providing conditions favorable to the drain of the water, much better than what can happen in a flat land where you often have to provide artificially, digging into the subsoil up to an adequate depth and filling the excavation with pieces of stone, pebbles, large fragments of bricks, in order to avoid a soil accumulation that would bring excessive moisture.
In general, the rock garden should never be placed in the shade of trees, nor located in such a way that the coldest winds hit it.
In the vicinity of the sea, even the salty winds will be of great damage, but in this case there is little to do since the slopes usually face the sea: where possible, we will try to artificially give the slope a slope as much as possible perpendicular to the coast line so that the salt brought by the wind does not beat directly on the plants.
In some gardens there are various levels of terrain and, unless the overlying ground is supported with retaining walls, it is difficult to keep the entire difference in level; the construction of a rocky cliff-shaped garden will make such a position attractive and will avoid many inconveniences connected to the maintenance of normal connecting works or of grassy prunings.
Do not forget, in case you can choose the position in which to place the rocks, that the construction of the garden will involve a considerable weight of land and stones, whose transport will be very facilitated if the chosen place will be near a path: the move of the material would be greatly intertwined if it were to be carried out between flower beds or on large lawn extensions and could also result in damage to the other parts of the garden.
So, if the rock garden must be accompanied by the flow of a stream and small waterfalls, this can be done by using electric motors and pumps (see Fountains in the garden), but some measures must be implemented.
Care should be taken that the chosen position is close to the electrical connection, in order to allow the cables to travel as little distance as possible, and to a water intake, to avoid excessive transport fatigue, when it must be replaced by re-filling the quantity of water lost by evaporation, dispersion or seepage.
The pools and the bed of the stream should be made of cement, more durable than plastic, made during construction and left to dry perfectly before proceeding further, to avoid any cedi- actions and cracks; also the plastic, if it will be used, must be incorporated during the work, in the desired position.
The pipe that will bring the water from the pump to the upper basin will have to be installed almost at the beginning of the construction, because it would be very difficult to hide it later, when the boulders had been placed in the right position: its path must be marked order not to produce damages during the implementation of the following parts and at least one meter must be left exposed at both ends, so as to make the necessary fittings possible.
As for the rock, the best thing is always to use the local stone that will seem more natural and will adapt in the best way to the surrounding environment; moreover the transport of the necessary masses, obviously quite big and heavy, is quite expensive and it is, therefore, preferable to trace them as close as possible to the place where they will have to be placed. It can be said that in Italy only the Po Valley is distant from quarries or mountains where the stones can be traced, because the rest of the country is normally stony, both in the mountains and in the hills, and the qualities of the rocks can be very many.
Some of them, although they are reputable material soft enough to be etched in order to form irregular holes and pockets on the surface, where many plants will grow very well.
It is logical that, having traced the necessary rocks in the vicinity, it will not be possible to choose their quality as regards the siliceous or alkaline composition; therefore it will be necessary to ascertain their nature, although empirically: some drops of lemon or vinegar on the surface will already give a sufficient clue, sizzling and producing a slight effervescence in the presence of limestone.
The plants must be generally adapted to the type of rock, avoiding that absolutely calcifuge on strongly alkaline rocks; however, in many cases and for many plants it will be sufficient to abound in soil and acid soil to allow their life in good condition even on limestone.
The soil has a decisive importance and must consist of a mixture of good fibrous and fertilized earth, of humus in the form of earth of well-ripened leaves and peat, or crumbles of crushed stone, coarse sand, and fine gravel.
The proportions should be approximately 4 parts, 2 parts and 1 part and 1/2 respectively and can be mixed with a generous amount of bone meal.
The amount needed varies considerably depending on the extent of the garden and its location; it is evident that building the entire relief on a flat surface will require a larger amount of soil than it takes to build the plant on a naturally steep ground, since it will be a solid base to the rocks that will come hand placed on the surface.
The preparation of the place chosen for the construction is very important: first of all it is necessary to make sure of the efficiency of the drainage, increasing it if the earth is too compact and crowded; therefore it is necessary to establish in general the shape and the size of the construction to be carried out, marking in some way, with posts stuck in the ground or other, the general planimetry.
Preparing an exact plan is almost impossible because the final result of the work will be determined by the shape and size of the rocks, which is very difficult to evaluate, even if you can view in general the complex you want to get, especially if the chosen area is already naturally steep.
The steps and steps that go through the rock garden must be done first, in order to be able to move more easily and to delimit the areas of construction; the steps should never be perfectly in the center but moved as far as possible to create areas of irregular size.
If the garden is built on a slope, it is easier to descend the rocks from top to bottom, placing them in place; if instead the ground is flat, obviously the work will be more complicated and tiring and the rocks will have to be mostly raised on the artificial base of land that will be built, proceeding in ascending direction.
Care must be taken that the stones are all facing in the same direction and have roughly the same angle so that they appear as the result of a natural outcrop and not of a disorderly eruption that has scattered them in bulk.
The work must be done with care, no matter how long it will take, because it is good that every subsequent step is well established before proceeding further, in order to avoid any future failure; it would be good if the base of land, especially if artificial, was consolidated by rain, or at least watered very copiously so as to make it stabilize well (as when building roadbed roads), before placing additional weights on top.
Above all, it is important not to be dismayed by piles of stones and earth and not to rush to put them “on site” to clear everything: you would have to start over again because you have mistaken the positions of the stones or because the soil, not well arranged, can cause dips or can run off the first rain, smearing everything and causing the stones to move.
If the rock garden is built in the plains, without even a natural slope, it will often have to be, in practice, made up of a small artificial hill, with two or more slopes, and in this case it is even more important that the soil is consolidated to perfection at every stage of the job.
A variant of this last type of plant can be given by the construction of a wall with two sides, much higher than wide, but containing soil between the two side walls and the rather rough stones between them: this will not be a real garden rocky, but can accommodate a number of rupicolous and rudimentary plants and will be less encumbered in a small garden.
In coastal rock gardens for xerophytes and xerophytes, drainage is even more important, if possible, that in the traditional rock garden, sometimes there is also the difficulty of having a part made up of only rock: the construction, in this case, must be done on the contrary, chiseling the rock itself to build pockets, bags and platforms to be filled with soil so as to be able to place plants that are content, yes, of little land, but which certainly can not live without having at all.
Often, however, coastal landslides are composed of rocks mixed with the ground, especially in parts a little apart from the sea, and in this case we will proceed as for the implantation of any other rock garden, with the advantage of being able to use the stones existing on the spot, replacing the voids with which they were extracted with terracotta he will have left.
Naturally, suitable plants will be even more specialized than those used in the hinterland: small evergreen shrubs, mostly conifers, normally used, will be replaced by low myrtle or juniper bushes, to be kept in shape by careful pruning; the height can be given, in positions sheltered from the salty winds, from Arbutus unedo cultivated as small tree; the Brotocarpus, as well as the Portulaca grandiflora, they can be too intrusive and must be cut and multiplied from one year to the next, because they form a large quantity of ground waste; Cactaceae, Crassulaceae, Euphorbiaceae will provide excellent plants of all sizes and position together with Agave, Aloe, and other succulent Liliaceae.
We have said that in lowland climates, where rock plants often can not live, you can also build a rock garden using normal perennial or annual herbaceous plants. In this case, the plant will not be very different from the normal one, but it will often be flatter and more like a cliff than a mountain landscape. The used evergreens will be dwarf or prostrate conifers, the flowering plants will have to be largely changed during the various seasons and will consist of the dwarf varieties of Tropaeolum, Dianthus chinensis, Begonia x tuberhybrida and semperflorens, etc.
In spring we will use various small bulbous plants such as Crocus, Tulipa kauffmanniana, stellata, and other botanical species, and also Myosotis, Viola tricolor, Bellis.
As perennials, many types of Sedum, Sempervivum, and other Crassulaceae that resist the climate of the plains will be used. In this type of rock garden, which is rather tiring due to the necessary rotation of plants, but which can be very attractive, the most important thing is the choice in the combination of the colors of the flowers. If this choice is made with taste, the result will be lively and graceful and will not make you regret the most sophisticated gardens formed by mountain plants.
News and curiosity obout the rock garden
Among the treatises written on the gardens, very interesting is “Les Jardins”, published in 1782 by the abbot Jacques Delille (1738-1813) estimated in his time as a great poet, a member of the French Academy and a translator of Latin classics and Greeks.
His fame, like that of many poets of the period devoted more to form than to the essence of poetry, did not survive for long, but his precise technical descriptions allowed him to write this curious book: curious as it is a poem in verses, divided into four songs.
In the first he gives advice on the choice of land and on how to increase prospects and pleasant landscapes; in the second one teaches the art of planting trees and shrubs; the third is dedicated to flowers, rocks, meadows, and water; the fourth deals with the artificial ornaments of the gardens. Although its verses are artificial, it is one of the few complete treatises on gardens entirely written in poetry.
Read also: Albizzia (Leguminosae)