Spring is the best time to make a rock garden. When the important matter of the proper site has been put in the past, a definite scheme must be planned. Upon the definiteness of this scheme, much of the success of the rock garden will depend. Here desire will have to be subservient to the situation. It is not so much what you want as what is best in the circumstances.

Do not attempt slavishly to copy the rock garden of some one else. All the money in the world would not create an exact duplicate for you, since nature has made no two rocks precisely alike. Study them, of course; get all the ideas you can. But study first, and most, nature—more particularly its ways in your own neighborhood. Anywhere there is abundant opportunity. Take a leaf or two from the book of the Japanese gardeners. They are past-masters of the art of making rock gardens, with a bit of water thrown in. They make use of comparatively few blossoming plants, but their example is invaluable in the disposition of rocks with simple effectiveness, in the simulation of height and distance, in the proper employment of turf, and in the planting of such small trees and shrubs as are suitable for a rock garden scheme.

Measure carefully the space at command, and then lay out the plan on cross-ruled paper. Call each of the little squares a square foot and the labor will be made easy. Next, figure out a good entrance, and, if possible, an equally good exit—the one invisible from the other. Then outline the main path, which should be as devious as the situation allows, and, if byways cannot be added, provide for bays, or more pronounced recesses. Remember that you are not merely to simulate nature; you are, by a process of compressing much in little, to epitomize it.

Then comes the selection of the rocks. Usually the rock close at hand, perhaps on the very grounds, will answer every purpose. If you are not fortunate enough to own any, very likely there is more than one townsman who will be glad to give you all the boulders and smaller rocks that you want, if you will only remove them from spots where they are not desired. The cost of removal, even in the case of boulders of fair size, is not great.

Barring quartz rock, which does not look well, almost any kind of natural stone may be made use of to the best advantage. Artificial stone should be shunned like the plague. Limestone and sandstone are good materials; granite is better. Granite, however, does not stratify, and if stratified effects are desired, another stone must be selected. A good plan is to use more than one kind, but to keep them properly apart. Weather-beaten granite is excellent material, and, in general, it is well to have the rock look anything but newly quarried. Pick out some rocks with a growth of lichen on them, and be sure that this is not disturbed by the moving.

Boulders may run up to several tons in weight. Where none is readily obtainable, one can be simulated by ingeniously combining a few small ones and concealing the joints by the planting of such things as stonecrops in earth—which, save in rare cases of sheer necessity, is always used in the construction of a rock garden in place of mortar.

If the site is level, the next step is to change all that—first on paper. Unless the lay of the land is all right at the outset, the configuration of the rock garden must not depend wholly upon the upbuilding; there must be some excavations, but no depressions deep enough to catch and hold water just where you will want to walk.

Aside from the path levels, building begins with the rocks, not with the soil. This is a highly important point. Place the boulders first; they are the big effects. Aside from that, the heaviest work will be out of the way. Then start in with the outlining base rocks. These should be placed with the largest surface to the ground and should vary in size. It is not essential that the lowest rocks should be slightly buried in the ground, but that course is preferable.

When the paths and outer margins have been thus defined, scatter more rocks over the intervening surface, placing them fairly thick but not close together. Next, fill in with soil, packing it firmly and ramming it hard into every crevice. If it fits in with the day's work, it is not a bad plan to water the rock work well in order to pack the soil, and when resuming the labor on the morrow, to add more soil, well pressed down, before proceeding with the second layer of rock.

This second layer should have the rocks placed with the front edge slightly back from that of the lower row in order to form a slope, though an occasional overhang may be fashioned if required for a certain plant known to abhor a drip from above. The construction then proceeds as before, until the desired height is reached. The height is entirely arbitrary, but some points should be at least as high as the line of vision, as one of the great advantages of a rock garden is the pleasure of enjoying some of the typical rock plants without stooping. The rocks used as fillers should overlap here and there to give strength, but care must be taken to contrive plenty of long soil runs. Eighteen inches should be the very least. A plant like the alpine androsace is a tiny rosette, seemingly requiring no more than an inch or two of soil, but its roots are likely to be found following an earth-filled crevice in the rocks to the depth of a yard or so. It is because of this deep penetration of roots that the soil should be packed so very firm; the roots must be in no danger of loose soil or of striking a hidden hollow.

At no point between two stones should the layer of soil be less than two or three inches thick after being packed hard. If an upper stone is likely to bear down too heavily and crush the plant roots, this may be avoided by placing small stones here and there in the layer of soil. The roots will work between these stones, but there must be a continuous, though not necessarily straight, soil run from the front of the rock work to the solid filling of earth. The run should slope downward slightly.

Rocks calculated to simulate a natural stratification ought to be laid on an incline for proper drainage. Such pieces of rock may also be employed sparsely in wedging, and in the making of the so-called "pockets."

These pockets are of prime importance in the construction of a rock garden. They hold the only considerable spaces of soil and are the chief means of colonizing plants, thus providing for pronounced color effects. They should break the slopes and be irregular in size, shape, and distribution. The large ones may be easily subdivided by small stones when the planting is done if a further separation of species is desirable. The soil must slope a little from the top, so that there will be no standing water.

The drainage of a rock garden is of vital importance. There must be plenty of moisture stowed away behind the rocks against the heat of summer, but all excess must be carried away. The garden should drain naturally, as the hills do. If any doubt exists, make a drainage bed of eight inches of clinkers before starting to lay the stones.

The soil should be a good loam with a little peat, and stones varying in size from a mustard seed to an almond. A little manure may be used, but it must be old.