262 



ALPINE PLANTS 



ALPINE PLANTS 



season of 170 days and upward. This is computed 

 by adding the days from the last frost of spring to the 

 first frost of autumn. At New York, the season is 210 

 days, at Philadelphia, 220 days, and of course constantly 

 increasing southward. 



On account of this long growing season and also 

 because of the dry, hot character of the winds, it is 

 almost impossible, without great expense, to main- 

 tain an alpine garden in this region. The same is true 

 of the coastal part of the Pacific coast, and in the Missis- 

 sippi Valley up to about St. Louis. This is, of course, 



174. Arrangement in a rock-garden 

 to insure sub-irrigation. 



a general statement, and peculiarly favorable local con- 

 ditions within the areas specified may be found, where 

 the attempt can be made. But it is extremely doubtful 

 whether any really good alpine garden can be maintained 

 within this area permanently without a great mainte- 

 nance expense, in the way of constantly supplying new 

 plants, keeping the garden regularly cooled down by 

 water and the like. 



As one goes back from the coast, even a few miles, there 

 is a marked change in the climate, and particularly 

 noticeable is the constantly diminishing length of the 

 growing season. Near Hartford, the Highlands of the 

 Hudson, northern New Jersey and Pennsylvania, the 

 growing season averages from 138 to 120 days, more or 

 less. As a general rule it may safely be stated that any- 

 where east of the Mississippi where elevations of 1,000 

 feet or greater are found, an alpine garden is permissible 

 except in the southern Alleghanies, where greater ele- 

 vations must be sought. This length of the growing 

 season is easily computed for all parts of the country, as 

 Indicated above; and wherever we find an active grow- 

 ing season of 100 to 140 days, it would be profitable 

 to make an alpine garden. In the East it will be found 

 that the short season is almost always correlated with 

 elevations in excess of 1.000 feet and in the West at 

 several times that altitude. 



Position of the alpine garden. 



So far as our purpose is concerned, there are three 

 classes of alpine plants: (a) those that require full sun- 

 light, (6) shadfr-mhabiting species, and (c) those that 

 are apparently indifferent as to exposure. To meet all 

 these conditions within a single garden is not always 

 possible, and a selection of plants must therefore be made, 

 unless one is fortunate enough to have a situation that 

 combines these requisites. As a general rule it is better 

 at some distance from a dwelling, stable, or garage, 

 both architecturally and culturally. No class of plants 

 is quite so wild as alpines, and the more secluded the 

 garden, and the greater the suggestion of sequestered 

 nature the better. A screen of evergreens or other trees, 

 and a northward-facing slope, insuring good drainage, is 

 perhaps the best all-round combination that one could 

 desire. If the garden is at a slight elevation above the 

 immediate surroundings, so much the better; although 

 this is not absolutely essential. Southern or western 

 exposures are to be avoided unless the garden is at 

 least 4,000 feet above the sea in the East, and from 

 6,000 to 8,000 feet in the West. It should also be 

 arranged so that drainage will not be entirely down 

 through the soil as in ordinary gardens, but rather so 



that the water can trickle from the roots of those above 

 to those below. This is often best attained by a judi- 

 cious use of rocks, which will be considered later. 



Making the garden. 



Having decided that one lives within the area in which 

 it is safe to begin the installation of an alpine collection, 

 the next most important consideration is to give the 

 plants the requisite local condition. Nearly all of them 

 require good rich soil, at least 18 inches deep, preferably 

 deeper. Even those species that grow in the crevices 

 of the rocks in their native habitat do so not because 

 they "like" such situations, but most probably because 

 no more favorable place is available. 



In preparing the soil, it is well to remember that at 

 least one-third of the mixture should be fine rotted 

 leaf-mold mixed with equal parts of loam and sand. 

 The latter is quite necessary in order to insure perfect 

 drainage. It has been stated that some alpines will 

 thrive in situations that approximate our bogs in hav- 

 ing a high humic acid content. But most of the species 

 thrive where the drainage is good and the soil is sweet, 

 not sour. 



If for no other reason than to insure perfect drainage, 

 it is best to construct the garden in a series of terraces 

 with walks of more or less irregular outline between, as 

 taste and convenience dictate. Avoid all semblance of 

 formality in the arrangement of these terraces, as 

 artificiality or formalism in the alpine garden are quite 

 the least desirable features to be sought. 



The terraces, or any modification of them, are best 

 held in place by a more or less free use of rocks. The 

 placing of these requires great skill and taste, as their 

 purpose must be twofold to add a sense of naturalness 

 to the garden and to make suitable pockets in which to 

 grow the plants. While it is true that many alpines, 

 such as Thalictrum aquilegisefolium, Clematis recta, 

 Aconitum Lycoclonum, Digitalis ambigua, Polemonium 

 cxruleum, Gentiana asclepiadea, and Delphinium elatum, 

 with many others, can be grown without the use of 

 rocks, it is true, on the whole, that most alpines grow 

 better and seem more at home when rocks are part 

 of their environment. Just what part the rocks play 

 in the home economy of the plants is not very well 

 understood, but the readiness with which they conduct 

 the water to the roots, and their tendency to keep the 

 soil cool both suggest themselves as possible benefits. 



For such species as Phlox Douglasii, Cassiope Mer- 

 tensiana, Polemonium montrosense, and all plants of 

 their type whose natural home is at elevations from 

 10,000 to 12,000 feet, care must be taken to insure almost 

 constant sub-irrigation of cool water. In their native 

 habitats, such plants have their roots constantly in 

 the icy water of the substratum, and any conditions 

 that do not approximate this will make failure almost 

 certain. 



An arrangement for insuring this sub-irrigation is 

 figured in Fig. 174, diagramatically. The pocket of 

 soil in the rocks having been filled with the proper soil 

 mixture, the water may be let in at a, with a rock just 

 in front of the pipe to insure the water's downward 

 passage (d). With the bottom made water-tight by 

 concrete or rocks and clay, and the outlet regulated at 

 6, a definite water-level can always be maintained at c. 

 The outlet can be arranged as indicated to flow either 

 over the surface of the rock below or in a pipe behind 

 it. If the water for this plan comes from a cool spring, 

 so much the better. The smallest stream of water is 

 sufficient, as it is not the water itself with which one is 

 aiming to supply the plants, so much as the cooling of the 

 soil, rocks and atmosphere that ensues from a gentle 

 flow of water through and around the soil and rocks. 



Such measures are not necessary for all alpines, but a 

 few species must be grown under condit ions approximated 

 by these methods. The expense of installing and main- 

 taining such construction, however, is relatively great, 



