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The [[Japanese rock garden]], in the west often referred to as ''Zen garden'', is a special kind of rock garden with hardly any plants.
The [[Japanese rock garden]], in the west often referred to as ''Zen garden'', is a special kind of rock garden with hardly any plants.
{{Inc|
Rock-Garden. An ornamental planting in very rocky places or in areas on which rocks have been placed for the particular purpose to make congenial conditions for certain classes of plants and also to lend interest and variety to a part of the grounds; a rockery. Figs. 3415-3419. See, also, Alpine Plants, Vol. I.
species that have been long cultivated there. Here alpines have been but little undertaken. A very few easily grown European kinds, as Aubrietia deltoidea, Achillea tomentosa, Campanula carpatica, and Arabis albida, are offered by American nurserymen and cultivated in the open border. On a few private places small rock-gardens have been established, or advantage has been taken of favorable local conditions to cultivate some additional species, and in one or more botanic gardens considerable collections have been at times maintained, chiefly in frames. Generally what have passed for rock-gardens have been rockeries— mere piles of cobbles raised from the surface of turf or piled against dry banks in such a manner as rapidly to disperse instead of slowly conserve all soil-moisture. Even the most self-assertive weed fails to thrive in such a garden.
In general, we have a smaller rainfall, less humidity and a larger proportion of sunny days than in England, to which we must look for careful instruction in the cultivation of alpine plants. This must be regarded in the arrangement of our rock-gardens. Every precaution should be taken to secure the full advantage of rainfall and any natural water-supply, and there should also be a liberal and constant artificial water-supply. It must be kept in mind, also, that at low elevations the long hot summers do not allow the period of rest that such plants require. This condition must be met by devices, methods, and locations that will retard the growth in spring, check it at an early period in autumn, and keep the plants fully dormant in winter, such as shade, mulching, and, in the case of particularly difficult plants, the protection of frames. It is essential that conditions be provided that will enable the roots to extend for a long distance, often many feet, in narrow crevices and pockets between rocks to depths where there is a uniform temperature and uniform moisture supplied by moving water, for frequent freezing and thawing and stagnant water are fatal. These cavities should be filled with such loose material as fragments of rock mixed with decayed vegetable matter, without manure, and arranged to provide for the free passage of hair-like roots, for perfect drainage and the free access of air. To provide these unusual conditions on the average private place in a large way would be so difficult and so expensive that it is not to be recommended. A small collection, comprising a few easily cultivated alpines and the similar rock-plants referred to in a later paragraph may, however, be successfully grown on reconstructed stone walls, on ledges, in small rock-gardens and in the open borders of almost any country or city place. Persons who desire to cultivate a large collection of true alpines should seek a situation where favorable natural or existing conditions may be taken advantage of. Such locations are likely to be found at the seashore and in rocky and hilly regions—such regions, for example, as are chosen by many persons for summer homes. A ledge, a natural mass of boulders or an abandoned quarry will often provide them. Pockets and crevices of ledges may be cleared of unsuitable material, and if they are not deep enough to hold moisture and have an equable temperature their-depth may be increased by the judicious use of wedges, bars, and explosives. Boulders can be arranged in such a manner as to secure suitable deep pockets and crevices of soil, springs can be diverted to supply a constant flow of water, underground pipes can be carried from an artificial source of supply to various points where conditions require them. However favorable the conditions are, it will be found that much can be done to advantage in different localities to meet the special requirements of different groups of plants. In such work, however, it should be kept constantly in mind that there are plants that will grow in all sorts of surroundings, and that it will often be much better to seek such as are adapted to existing conditions than to go to the expense of radically modifying such arrangements.
If an -artificial rockery is to be constructed, it should be borne in mind that it is not for the purpose of displaying a collection of curious rocks fantastically arranged, but to provide a place for growing a class of plants that cannot be so well grown elsewhere. It would be better never to think of securing mountain, valley and rock effects in the disposition of the material to be used, but only to think of providing many varied conditions and situations as regards exposure to sun and shade, depth of pockets and crevices, the character and depth of soils, subterranean and surface water-supply, and whether it be permanent or fluctuating. In selecting and arranging the rocks, freshly broken raw faces should not be exposed, but rather such faces as are already covered with a growth of lichens for sunny places and with mosses for shady spots. To take full advantage of surface water, pockets and crevices should have a decidedly downward direction from the exposed surface and not be sheltered by overhanging rock. That this does not apply in all cases, those who are familiar with the habitats of rock-plants know full well. The natural habitat of Pellaea gracilis in the upper Mississippi bluffs is in horizontal crevices well back from the edge of the overhanging rock, where it is absolutely protected from all surface water. It finds sufficient moisture in the horizontal seams. Pellaea atropurpurea will grow in narrow cracks and small pockets on the face of dry limestone boulders where there can be no possible internal supply of moisture. These examples go to show that the general principles that will apply to such plants as a class will not apply to all species, and it simply gives emphasis to the importance of trying a plant under all sorts of conditions before assuming that it can not be grown. The writer remembers well an attempt to grow that most exquisite alpine flower, Gentiana verna, in the open border on a little pile of rocks to give it suitable drainage. It was transplanted a number of times to places where its environment appeared to be about the same, and finally a situation was secured, where, instead of barely holding its own, it increased and produced a number of its great deep blue flower-cups.
Nature in time will make a garden even on the broken surface of a rock, by clothing it with lichens, algae, and mosses of many exquisite forms having much variety and often striking brilliancy in coloring. If there are soil-filled cracks and pockets, then ferns and flowering plants will find a place. At low elevations, however, these flowering rock-plants are comparatively few, for soil accumulates rapidly and strong-growing herbs, shrubs, and trees, aided by favorable climatic conditions, soon cover the rock surface or furnish so dense a shade that only mosses, lichens, and ferns will thrive.
The ideal rock- or alpine gardens are within that region on mountain summits between the limits of tree-growth and the edge of perpetual snow, and in the corresponding regions toward the poles, where the plants are protected from the rigors of a long winter by
blankets of snow and are quickened into a short period of rapid growth by a comparatively low summer temperature. Here, where there are deep cool moist rock-crevices and pockets filled with fragments of broken stone and porous decayed vegetable matter, are the favorable conditions wherein the real alpine plants can multiply their neat and dainty cushions, tufts, and rosettes of dense and matted foliage and their abundance of exquisitely formed and brilliantly colored flowers. A successfully grown collection of these plants in contrast with ordinary garden flowers would be like a collection of cut gems as compared with one of rough minerals and rocks, for they nave an exquisiteness of finish and depth of coloring that gives them as unique a place in the vegetable kingdom as they have in the plan of nature. Surely there are men and women who, if they knew these plants well, would be fired with an ambition to excel in their cultivation; and in so doing they may enter a comparatively untrodden path if they will limit their work chiefly to the alpines of this continent. They are represented in the New England mountain region by such species as Arenaria graenlandica, Loiseleuria procumbens, Silene acaulis, Diapensia lapponica, Arctous alpina, Vaccinium caespitosum, Saxifraga Aizoon var. rivularis, Veronica, alpina, Geum radiatum var. Peckii, Sibbaldia procumbens, Rhododendron lapponicum, Phyllodoce caerulea, Primula farinosa, Saxifraga oppositifolia, S. Aizoon, and S. aizoides, Aster polyphyllus, and Woodsia glabella; and in the Rocky Mountains and Pacific Coast ranges by Erigeron uniflorus, E. lanatus, and E. ursinus, Actinella Brandegei and A. grandiflora, Artemisia borealis, A. scopulorum, and A. alpina, Senecio Soldanella, S. Fremontii, S. petraerus, S. uniflorus, and S. werneriaefolius, Crepis nana, Campanula uniflora, Primula Parryi and P. suffruticosa, Androsace Chamaejasme and A. septentrionalis, Gentiana prostrata, G. frigida, G. Newberryi, G. Parryi, and G. simplex, Phlox bryoides and P. caespitosa, Polemonium confertum, Cassiope Mertensiana, Phyllodoce Breweri, Draba streptocarpa, D. Parryi, and D. nudicaulis, Arabis Lyallii and A. platysperma, Smelowskia calycina, Lychnis montana and L. Kingii, Calandrinia pygmaea, Claytonia megarrhiza, Spraguea umbellata, Dryas octopetala, Geum Rossii, Saxifraga chrysantha and S. bryophora, Cystopteris alpina, Aplopappus pygmaeus, A. Lyallii, and A. acaulis, Omphalodes nana var. aretioides, Chionophila Jamesii, ana so on. (Not all of these names are accounted for in this work. They may be found in the current manuals of North American plants.)
The uncultivated American plants in this class are quite as numerous and attractive as are the European species that have been long cultivated there. Here alpines have been but little undertaken. A very few easily grown European kinds, as Aubrietia deltoidea, Achillea tomentosa, Campanula carpatica, and Arabis albida, are offered by American nurserymen and cultivated in the open border. On a few private places small rock-gardens have been established, or advantage has been taken of favorable local conditions to cultivate some additional species, and in one or more botanic gardens considerable collections have been at times maintained, chiefly in frames. Generally what have passed for rock-gardens have been rockeries— mere piles of cobbles raised from the surface of turf or piled against dry banks in such a manner as rapidly to disperse instead of slowly conserve all soil-moisture. Even the most self-assertive weed fails to thrive in such a garden.
In general, we have a smaller rainfall, less humidity and a larger proportion of sunny days than in England, to which we must look for careful instruction in the cultivation of alpine plants. This must be regarded in the arrangement of our rock-gardens. Every precaution should be taken to secure the full advantage of rainfall and any natural water-supply, and there should also be a liberal and constant artificial water-supply. It must be kept in mind, also, that at low elevations the long hot summers do not allow the period of rest that such plants require. This condition must be met by devices, methods, and locations that will retard the growth in spring, check it at an early period in autumn, and keep the plants fully dormant in winter, such as shade, mulching, and, in the case of particularly difficult plants, the protection of frames. It is essential that conditions be provided that will enable the roots to extend for a long distance, often many feet, in narrow crevices and pockets between rocks to depths where there is a uniform temperature and uniform moisture supplied by moving water, for frequent freezing and thawing and stagnant water are fatal. These cavities should be filled with such loose material as fragments of rock mixed with decayed vegetable matter, without manure, and arranged to provide for the free passage of hair-like roots, for perfect drainage and the free access of air. To provide these unusual conditions on the average private place in a large way would be so difficult and so expensive that it is not to be recommended. A small collection, comprising a few easily cultivated alpines and the similar rock-plants referred to in a later paragraph may, however, be successfully grown on reconstructed stone walls, on ledges, in small rock-gardens and in the open borders of almost any country or city place. Persons who desire to cultivate a large collection of true alpines should seek a situation where favorable natural or existing conditions may be taken advantage of. Such locations are likely to be found at the seashore and in rocky and hilly regions—such regions, for example, as are chosen by many persons for summer homes. A ledge, a natural mass of boulders or an abandoned quarry will often provide them. Pockets and crevices of ledges may be cleared of unsuitable material, and if they are not deep enough to hold moisture and have an equable temperature their depth may be increased by the judicious use of wedges, bars, and explosives. Boulders can be arranged in such a manner as to secure suitable deep pockets and crevices of soil, springs can be diverted to supply a constant flow of water, underground pipes can be carried from an artificial source of supply to various points where conditions require them. However favorable the conditions are, it will be found that much can be done to advantage in different localities to meet the special requirements of different groups of plants. In such work, however, it should be kept constantly in mind that there are plants that will grow in all sorts of surroundings, and that it will often be much better to seek such as are adapted to existing conditions than to go to the expense of radically modifying such arrangements.
If an -artificial rockery is to be constructed, it should be borne in mind that it is not for the purpose of displaying a collection of curious rocks fantastically arranged, but to provide a place for growing a class of plants that cannot be so well grown elsewhere. It would be better never to think of securing mountain, valley and rock effects in the disposition of the material to be used, but only to think of providing many varied conditions and situations as regards exposure to sun and shade, depth of pockets and crevices, the character and depth of soils, subterranean and surface water-supply, and whether it be permanent or fluctuating. In selecting and arranging the rocks, freshly broken raw faces should not be exposed, but rather such faces as are already covered with a growth of lichens for sunny places and with mosses for shady spots. To full advantage of surface water, pockets and take crevices should have a decidedly downward direction from the exposed surface and not be sheltered by overhanging rock. That this does not apply in all cases, those who are familiar with the habitats of rock-plants know full well. The natural habitat of Pellaea graciliis in the upper Mississippi bluffs is in horizontal crevices well back from the edge of the overhanging rock, where it is absolutely protected from all surface water. It finds sufficient moisture in the horizontal seams. Pellaea atropurpurea will grow in narrow cracks and small pockets on the face of dry limestone boulders where there can be no possible internal supply of moisture. These examples go to show that the general principles that will apply to such plants as a class will not apply to all species, and it simply gives emphasis to the importance of trying a plant under all sorts of conditions before assuming that it can not be grown. The writer remembers well an attempt to grow that most exquisite alpine flower. Gentiana verna, in the open border on a little pile of rocks to give it suitable drainage. It was transplanted a number of times to places where its environment appeared to be about the same, and finally a situation was secured, where, instead of barely holding its own, it increased and produced a number of its great deep blue flower-cups.
The importance of protection from drying and cold winds and of securing shade in many situations must not be overlooked. Sometimes advantage may be taken of an existing deciduous or evergreen tree or shrub growth, or rapid-growing varieties may be planted to make a screen. While shelters of this character are of value about the outer limits of a rock-garden, they can hardly be used for separating its smaller compartments.
For this purpose, slow-growing dense-foliaged evergreens with a restricted root range are best. This would include the yuccas, a few of the dwarf forms of thuya, juniperus, picea, retinispora and practically all the broad-leaved evergreens. The latter, especially the rhododendrons (of which Rhododendron maximum can be secured in large plants at low cost), are particularly useful owing to their habit of growth, restricted root area, and the facility with which they can be moved from place to place as desired. As these shelter-belts and groups form the background and setting of the rock-garden and are the dominating landscape feature in views from a distance, their composition and disposition is a matter of much importance. The disposition must be governed, however, by the general arrangement of the ground, but in this arrangement an agreeably varied sky-line and composition of plant forms and of shades of green should be sought for. In the composition of the background, and in the planting of the rock-garden as well, a decided character should be given to the whole and to each distinct compartment by using some few effective plants in quantity rather than a great number of varieties in small quantities. Variegated and distorted garden freaks should be excluded, for they only distract the attention from the rock-garden, the primary object. Even more inappropriate are statuary fountains and vases.
Up to this point reference has been made for the most part to distinctly alpine plants, that is, plants that are confined exclusively to the region on mountains above the tree- and shrub-line. They are the ones that will test the skill of the cultivator. There are, however, many rock-plants, that is, plants that grow naturally on rocks, or plants having a tufted, matted, and more or less persistent and evergreen foliage similar to alpines, that can be used with them in less favorable positions in the rock-garden or in the open border. Many of such plants can be readily procured from American nurserymen and collectors. They are easy of cultivation and attractive in habit and flower. The writer would include also low-growing bulbous plants, especially such as have inconspicuous foliage. They may be planted with the low ground-covering plants to push up through them. From this list are omitted such plants as belong more properly in the wild-garden, especially such as spread rapidly by underground shoots and are likely to become a pest. (In a rockery conditions are such that it is almost impossible to extirpate deep-rooting, weedy plants, and they above all others should be rigidly excluded.) Among desirable rock-plants may be included Geranium sanguineum, G. Andrewsii, and G. Robertianum, Gypsophila muralis, Helianthemum vulgare, Helleborus niger, Leontopodium alpinum, Lin- aria Cymbalaria, Lotus corniculatus, Lychnis Viscaria, Papaver alpinum and P. nudicaule, Ceratostigma Lar- pentae, Saponaria ocymoides, Veronica Teucrium and V. rupestris, Arabis alpina, Campanula fragilis, Daphne Cneorum, species of Alyssum, Bellis, Cerastium, Arenaria, Draba, Epimedium, Iberis, Thymus, Arabis, Armeria, Ajuga, Dianthus, Sedum. Sagina, Primula, Aquilegia, Saxifraga, Corydalis, Myosotis, Semper- vivum, Parnassia, Viola, Hepatica, Opuntia, Houstonia, Anemone patens var. Nuttalliana, dwarf and creeping Campanulas, Cornus canadensis, Dicentra eximia, Calluna vulgaris, Iris cristata, I. verna, and I. pumila, Leiophyllum buxifolium, Phlox subulata, P. amoena, and P. reptans, Saxifraga virginiensis, Silene pennsyl- vanica and S. virginica, Anemone thalictroides, Wald- steinia fragarioides, (Galax aphylla, Asperula odorata, low-growing ferns, mosses, and the like.
For more specific instructions as to the construction of rock-gardens and the care and propagation of rock- plants (for European conditions), see Robinson's "Alpine Flowers," London, 1870, and Sutherland's "Hardy Herbaceous and Alpine Flowers," Edinburgh and London, 1871.
Warren H. Manning.
The making of a rock-garden.
A rock-garden must of necessity often bo "artificial" in the sense of made by man, because few gardens or grounds contain a natural rocky slope or even a natural bank upon which one might be constructed, and if they did the position may not be an ideal one. A southern slope would be too hot and dry in this climate, unless it was shaded by tall trees. A bank with a northern or northeastern aspect free from the roots of trees would suit this class of plants much better, and very attractive it can be made, especially if the bank is on the outer edge of a garden, or skirts a lawn. There is no form of gardening in which one has more opportunity to give expression to his natural taste than in the construction and planting of a rock-garden. But since all grounds or gardens do not have a natural bank or slope upon which an "open" rock-garden might be constructed, a depressed rock-garden may be made in grounds that are perfectly level, and some of the best rock-gardens in the world are what are known as "underground," for example, the one in the Royal Botanic Gardens, Kew, London, England. Before this rockery was constructed the ground was perfectly level. A cutting was begun at one entrance, at first shallow, but gradually deepening till a depth of some 6 or 7 feet was reached, and an average width of about 10 feet at the bottom. All the soil taken out was placed on the top of the slopes, thus still further increasing the height. The cutting was made in a winding manner, not ormal or zigzag,but in such a form that when completed, not only would a variety of aspects be secured to suit the requirements of different plants, but each turn should seem to possess a peculiar charm of its own. The whole cutting is perhaps some 200 yards in length. The rocks are placed in the banks in as natural a manner as it would seem possible to place them; now they stand out boldly, almost perpendicular with the edge of the path, then again they recede into hollow recesses. There are not too many rocks, nor yet too few. In one place a cascade falls over the rocks into a small pool which not only provides a habitat for aquatic and bog- plants, but also adds greatly to the beauty of the rockery. For the convenience of the public, a broad gravel path runs through the whole rockery. Rhododendrons and other shrubs are planted on top of the banks in groups, and not in straight lines, while behind these, for protection and shade, are planted pines and other conifers, as well as some deciduous trees. The rocks were placed in most cases so as to form "pockets" of good size into which the plants could be placed, and the soil made in the pocket to suit the requirements of the different plants. With such a variety of aspects and conditions, this rockery is able to accommodate one of the largest collections of alpine and rock-plants in the world. Deep carpets of mossy saxifrage, aubrietia, arabis, cerastium, sedum. and the like, hang over projecting ledges of rocks, while in fissures and holes in the rocks are growing those dainty rosette-making saxifrages, S. longifolia, S. Cotyledon, S. crustacea, and S. caesia, as well as the charming androsaces. In the deeper recesses of the rockery are to be found the large-leaved saxifrages, such as S. crassifolia, S. ligu- lata, S. Stracheyi, and S. purpurascens. Quite at home and in suitable positions are alpine primulas, auriculas, and cyclamens. There are Iceland poppies, Himalayan poppies (Meconopsis Wallichi and M. nepalensis), gentians from the tiny blue Gentiana verna to the tall G. septemfida, and many kinds of Hosta, Fritillaria, Erica, Epimedium, Cypripedium, Orchis, Lilium, Erythro- nium, Allium, Alyssum, Ajuga; Achillea, Armería, Sagina, Sempervivum, and creeping Veronica, besides other plants too numerous to mention. Particularly prominent positions, as on top of the rocks, or at a turning point in the path, are occupied by some stately plant, such as Rheum palmatum, Acanthus mollis, or Gunnera manicata, or G. chilensis, while foxgloves, ver-bascums, and such plants would fill up the recesses in the shrubs on the top of the rockery. One end of the rockery beneath the shade of overhanging trees is devoted to hardy ferns, which grow with wonderful luxuriance. With the variety of rare and interesting plants, together with the artistic yet natural appearance of the whole rockery, a more beautiful place it would be difficult to conceive.
In 1898, the writer built a rock-garden in the Botanic Gardens of Smith College, Northampton, Massachusetts, somewhat after the pattern of the one at Kew, but on a very much more limited scale. (Fig. 3419.) The position chosen (the only one available) is near the outskirts of the garden proper, on what was formerly a grassy southern slope. A cutting was made through the slope in much the same manner as the one at Kew, but to secure good northern aspects the soil was all banked on the southern side. The path, which is quite level, varies in width from 3 to 6 feet. The height of the banks in which the rocks are placed ranges from 2 feet at the entrances to some 8 or 10 feet at the highest point. For rocks, large water-worn boulders collected in the vicinity were used. One shaded recess, with a northern aspect, is devoted to native ferns, which at the present time, 1916, comprises some forty species. The whole rockery outside is banked with flowering shrubs, and on the southern bank outside are planted some trees, chiefly catalpas, for the purpose of shading the southern aspect of the rockery, as well as for ornament. Water is laid on so that the plants might not suffer in dry weather. The writer has not been successful with alpine primulas, mossy saxifrages, tufted gentians and several other subjects which delight in a cool, moist climate, perhaps from his not having provided the ideal conditions for such plants, but more probably due to our extremes of climate. Still there is a large variety which does well here. The writer has found most of the low- growing veronicas, sedums, sempervivums, arabises, alyssums, achilleas, alsines, erysimums, aquilegias, campanulas, stellarias, pachysandras, the beautiful shrubby little Daphne Cneorum, and many others, do very well in the more sunny or southern aspects of the rockery, while on the northern aspects cerastiums, iberises, ajugas, Iceland poppies, rosette and large-leaved saxifrages, moss pinks, epimediums, herniarias, arenarias, cardamines, armerias, dianthuses, native orchises, cypripediums, and many other plants do well. On the top of the rockery, to fill in recesses in the shrubbery, are planted foxgloves, verbascums, and tall veronicas, while at conspicuous points are planted clumps of Boc- conia cordata, Buphthalmium speciosum, Aruncus sylvester, or any herbaceous plant which looks well as an isolated specimen. In among the plants in irregular colonies are planted hardy bulbs, such as crocuses, scillas, ornithogalums, narcissi, snowdrops, chionodoxas, and grape hyacinths; these come up the first thing in the spring and blossom before the other plants get well started into growth, and are a decided acquisition to a rockery.
Almost all alpine plants may be readily propagated by seed, cuttings, or division of the plants. A good plan is to sow the seeds in 4- inch pots early in February in a finely prepared light soil, and place the pots in a moderately warm greenhouse; here they soon germinate, and as soon as large enough to handle they are transplanted either into other pots similarly prepared, or into small shallow boxes. They grow vigorously through the early spring months, and by the first of
May they may be planted out permanently. Seeds may also be sown in a shaded frame in spring and the plants tranferred to the rockery in autumn.
In planting a newly made rock-garden, it is a mistake to plant too thickly. Each plant should be given sufficient space for a reasonable growth, and to show its true character. Compact-growing and tufted plants may be planted closer than those of a spreading habit. All variegated-leaved varieties and plants having an aggressive habit or that cannot easily be kept within reasonable limits should be rigorously excluded from a rock-garden. The whole rock-garden should be replanted and fresh soil placed in the pockets about every four or five years. In dry weather a thorough watering should be given at least once in two days, and, as in other parts of a garden, weeds will insinuate themselves wherever they can gain a foothold; these, of course, should be removed as soon as they appear. In winter, the plants in the most exposed positions, such as those which overhang ledges of rocks, should be protected by branches of hemlock or pine laid lightly over them, and a light covering of half-decayed leaves or manure placed between most of the plants, especially on a southern exposure, protects them from excessive thawing and freezing. The general care required is usually much less than for an ordinary flower-garden, but the pleasure to be derived from a well-constructed and well-planted rock-garden is very much more.
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== See also ==
== See also ==