2970 



ROCK-GARDEN 



ROCK-GARDEN 



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 culti- 

 vated in the open border. On a few private places 

 small rock-gardens have been established, or advan- 

 tage 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 precau- 

 tion should be taken to secure the full advantage of 

 rainfall and any natural water-supply, and there should 



3416. A pocket in the rocks. 



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 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 

 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 

 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 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 con- 

 ditions require them. However favorable the con- 

 ditions 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 sur- 

 roundings, and that it will often be much 

 better to seek such as are adapted to 

 existing conditions than to go to the ex- 

 pense of radically modifying such arrange- 

 ments. 



If an artificial rockery is to be con- 

 structed, 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 grow- 

 ing 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 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 Pellsea gratilis 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. 

 Pellsea 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 moist- 

 ure. These examples 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 

 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 pro- 

 duced a number of its great deep blue flower-cups. 



