1540 



ROCK GARDENS 



the arrangement of our rock 'gardens. Every precau- 

 tion 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, too, 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 de- 

 vices, 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 diffi- 

 cult 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 



213S. A pocket in the rocks. 



thawing and stagnant water are fatal. These cavi- 

 ties should be filled with such loose material as frag- 

 ments 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 recom- 

 mended. A small collection comprising a few easily cul- 

 tivated 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 col- 

 lection of true alpines should seek a situation where 

 favorable natural or existing conditions can be taken 

 advantage of. Such locations are likely to be found at 

 the seashore and in rocky and hilly regions such re- 

 gions, for example, as are selected by many people for 

 summer homes. A ledge, a natural mass of boulders 

 or an abandoned quarry will often provide them. 

 Pockets and crevices of ledges can be cleared of unsuit- 

 able 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 condi- 

 tions are, it will be found that much can be done to 

 advantage in different localities to meet the special re- 

 quirements 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 sons of surroundings, 

 and that it will often be much better to seek such as are 



ROCK GARDENS 



adapted to existing conditions than to go to the ex- 

 pense 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 dis- 

 playing a collection of curious rocks fantastically ar- 

 ranged, but to provide a place for growing a class of 

 plants that cannot be as 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 con- 

 ditions 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 select- 

 ing 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 decid- 

 edly downward direction from the exposed 

 surface and not be sheltered by over- 

 hanging 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 Pellcea gra- 

 cilis in the upper Mississippi bluff's 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. Pellixa 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 in- 

 stances go to show that the general prin- 

 ciples 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 condi- 

 tions before assuming that it can not be 

 grown. The writer remembers well an at- 

 tempt 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 can 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 ever- 

 greens with a restricted root range are best. This 

 would include the Yuccas, a few of the dwarf forms of 

 Thuya, Juniperus, Picea. Retiriispora 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 grounds, 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 composi- 

 tion 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 



