There are many plants that succeed best when planted among rocks, and for their accommodation and to show off their beauties to the greatest advantage, it is common in large gardens to have an appendage, called a rockery. This is made of a collection of stones in the rough, or natural state, laid up without much order, with soil, which should be concealed as much as possible by the fragments of rocks.
As some plants succeed best in the shade, a portion of the rock work should be partly surrounded by trees.
Trilliums, Orchids, Cypripediums, and many other wild plants found in the woods and swamps, with an appropriate soil, would succeed very well in such a locality. I find an excellent article on this subject, written by my late friend J. E. Teschemacker, Esq., in one of the back numbers of the Horticultural Journal, which, as it is appropriate, I insert. He says:
"There are many plants with rather small flowers which possess exquisite colors and elegant forms; the charm of these is in a great measure lost by their being planted in the bed where the pitiless shower defaces their delicate tints with earthy splashes, or their distance from the eye causes their minute yet elegant characters to pass unnoticed; other plants run over the surface of the flower border to great distances, interfering with their neighbors, which would look much better hanging pendant from the crevice of a rock, or covering the sunny bank with their numerous blossoms.
"Nature, who is always an interesting and instructive teacher, points out such facts plainly, by often exhibiting these her treasures inhabiting and flourishing in the cracks of her wild mountain scenery, making it as interesting on a near approach, as it is astonishing at a distance.
Near Boston there are several glens, on a small scale, where the naked rock is beautifully ornamented by the Columbine, the Thalictrum, (Meadow-rue) the Violet, ferns and many other plants of great interest; they always appear to me more captivating in these their natural situations than when formally planted in the parterre.
In Europe, few gardens are considered complete without their compartment of rock work; and even where the spot is of the smallest size, a little piece of this device is frequently seen, filling up and concealing an ugly corner; nay, in the immediate vicinity of large towns where the kitchens occupy the places of the cellars in this country, the way down is sometimes metamorphosed into a rocky glen where Polypodiums, Aspleniums and other ferns flourish - one friend of mine near London has a place of this kind, where there is a collection of more than two hundred varieties of fern, many of them natives of this country, he writes to me - ' This I have turned into a rocky glen, planted all over with every variety of fern I could collect, and there are about 200 of them, in the several interstices between one piece of rock work and another, all growing beautifully, and presenting a singular and interesting contrast to the other surrounding species of vegetation. I am quite sure that if any horticulturist who has the least feeling for the beauty of form were to see it, he would not be long without taking the hint; the effect surpasses much what I expected.'
The nurserymen in the vicinity of London drive a considerable trade in these rock plants, as they are called, and generally keep them in small pots in appropriate mould, so that they may be purchased and transplanted at any time of the year; so great indeed has been, and I believe is still, the demand for them, that any one acquainted with the subject will know that the Alps, the Appenines, and every mountainous chain in the moderate climates have been ransacked for the purpose of adorning these faint imitations of nature's stupendous piles.
The first and great care in erecting rock work is to see that it does not resemble a pile of loose stones, the next that it is not built in a regular form, such as the segment of a circle or right line, as I have seen recommended in some works - then that the fragments of rock be of widely different sizes - for instance, a few small stones may fill a large interval between heavy masses, but there must neither be a mass of immense blocks together, nor a number of small ones piled on each other. It is by no means requisite that the whole rock work should constitute one mass; on the contrary, more variety is produced by having it in separate masses, with passages occasionally narrow and ruggedly rising, so that it is necessary to climb over a slight impediment to make the circuit - some art is required in arranging the crevices, so that the soil fit for each plant be not washed out by heavy rain, and the roots laid bare; the moss which grows on the surface of barren rocks is excellent for filling the lower part of these interstices, and in cases where plants that love a damp soil are cultivated, a garden pot with the hole stopped to hold water, and another with the plant placed in it, may be easily concealed - where there is water which might be made to trickle over the rock work this aid is not required. Due attention must also be paid to the aspect. Some flowers only open in the sunshine, others are only half hardy, for these the south and sheltered side is appropriate; ferns and many others, love the shade, and will not support the parching rays of the sun, these may clothe the northern aspect.