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Watering a rock garden is a matter of the utmost importance, which nevertheless is scarcely mentioned in rock garden literature. In England, of course, this is not so vital a matter as with us. With
less sun, more rain, and more moisture in the air, rock garden plants, especially alpines, are as apt to suffer from excessive moisture there as they are from lack of it here.
When speaking of the proper means of applying water, however, it is not in reference to either the watering can or a hose with the usual garden nozzle. The former takes too much time, and the latter applies water so rapidly that it will begin to run on the surface before the soil is saturated clear through.
But it is a simple matter to provide a mist like spray which will saturate the driest soil through and through without spattering mud on the smallest leaves or the most delicate blossoms, or causing the soil to run out from the most precarious rock crevices. There is a special type of greenhouse irrigation nozzle which applies the water in this fine mist like spray.
If this type of nozzle is substituted for the ordinary nozzles in a portable irrigating outfit, the rock garden can be watered with the utmost thoroughness and safety whenever necessary. Such a watering will last two or three times as long as one given with the ordinary watering can or hose nozzle.
Another option available is a short, brass tube fitted with a hose coupling at one end and one of these mist-throwing nozzles at the other—recommended for watering all fine seedlings or delicate plants. The hose, equipped with this nozzle attachment, may be supported in one position and left for a long time without any danger of overwatering.
For a large rock garden, however, a portable irrigating outfit of the nozzle-line type, with greenhouse nozzles in place of the ordinary garden or lawn nozzles, will be found the watering system par excellence. It is supported on metal rods which may be pushed down anywhere along the garden path or between outdoor statuary () without disturbing the growing plants and it may be set up or taken down in a few moments.
There is probably no question connected with rock gardening which is more of a bugaboo to the beginner than that of providing suitable soil, or soils, for the little friends whom he has invited into his garden and intends to do his best to make happy.
To read some of the works on this subject, the layman may easily get the impression that it is really necessary to provide each individual plant with a soil made up according to a special prescription! Nowhere in the whole broad field of gardening is "debunking" required more than here.
The secret of success with rock plants, so far as soil is concerned, is the old, old one of going back to nature and of taking a look at what she provides them with.
Drainage
If you climb up a rocky mountain slope to the timberline, to the bleak and native haunt of the alpines, or search out most of the other rock plants and find where they grow as wildlings, the most apparent characteristic of the soils in which they grow is plainly to be discerned—it is exceptionally excellent drainage.
Drainage not of the subsoil—as we usually speak of it in connection with flower garden, orchard, or field—but quick and complete drainage of the surface. Often the clumps of leaves of the little plant, hugging the ground closely as they must to preserve an existence, rest directly upon shale, gravel, splinters of rocks, or garden fountains, .
Our first consideration in supplying a man-made soil for this class
of plants should be porosity, assuring not only good drainage as we ordinarily use the term, but the immediate escape of all surplus water to the lower soil levels.
Moisture
If however, you attempt to pull up one of these tiny, and possibly rather frail-looking, denizens of the plant world, you get a sharp surprise. It is simply anchored fast, and will require much more effort to dislodge it than would many plants in your garden ten times its size.
In fact, if you could succeed in getting it out, roots and all—which would be extremely difficult—the most conspicuous thing about it would be the extreme length of the roots in proportion to the top. This would involve dredging up any soil, earth, rocks, or outdoor water features () that may be obstructing access to the roots.
If you could follow to where the roots penetrate, you would discover an unsuspected degree of moisture in the stone-filled soil; for stones, in spite of their dry appearance, are among the most efficacious of moisture conservers. Thus, in addition to exceptional drainage, we must add to our analysis an abundant moisture supply.
Plant Food
If we inquire still further into the life secrets of these little plants, and attempt to seek out their food sources of sustenance, we immediately strike a rock, both figuratively and literally. Most of our common garden plants would starve to death in the soil in which they thrive.
Vice versa, many of these little plants cannot long survive a diet of manure and fertilizers on which our garden plants grow lustily—although some of them, it must be confessed, will take to the change like ducks to water. It is apparent that a large supply of plant food, as we prepare it for our long domesticated garden flowers and shrubs, is one of the things that is not essential for the class of plants under consideration.
"Sympathetic" Stones
If rock plants ask for bread and you give them a stone, they will be very well satisfied—if it is the right kind of stone. Some rocks, due to their character and texture, are termed "sympathetic" to plant life. This depends, primarily, upon their porosity—the capacity for absorbing and storing moisture, and thus encouraging the creeping, thirsty roots to hug the rock and follow its surface deep down into the soil.
If you have roamed through fields and woods, or have stones about your own place, you have undoubtedly observed the difference among them in this respect. Some stones have a smooth, close-grained surface as impenetrable as marble; others are so porous that they will almost drink water like blotting paper.
Neither extremely hard nor extremely soft stones are best for rock garden making; the former are not "sympathetic" to plant growth, and the latter are not practical because they so quickly disintegrate
and crumble, often going to pieces in a single season when exposed to rains and frost action, although they may seem fairly substantial when put in place.
Types of Stone to Use
Hard, close-grained stones like granite are often used because they are easiest to get. If the pieces are irregular and with rough surfaces, as mined from a quarry, they will serve the appropriate purpose. Field stones or boulders, frequently found in places where there are glacial deposits, ground to smoothly rounded surfaces, are the least desirable.
Limestone or sandstone which shows a distinct grain or stratification, and obtainable in irregular blocks of varying sizes and shapes, is the most desirable. Field rocks, if not too small, are also brilliant, particularly if they have weather-beaten, or moss or lichen-covered surfaces.
Even in a small rock garden, it is well to have at least a few "old he-ones"—rocks which take a great deal of pushing and possibly some strong language to get into place; but which, once you get them where you want them, will give character to the entire planting.
They possess beauty and individuality no less than the plants with which they are to be associated. Japanese gardening is almost literally rock landscaping. In many of the wonderful compositions in Japanese gardening it is the plants, rather than the rocks, which are subordinated.
Tufa Stone is a volcanic rock, extremely ornamental both in form and texture, extraordinarily porous, light, easy to arrange, and in many ways desirable. Its cost, determined largely by freight charges, is not prohibitive for use in a small rock garden, especially where a picturesque or Japanesque effect is desired. It does not fit so well into a natural rock garden and looks best with a garden fountain, . This material is handled by many concerns which specialize in rock plants.
Other Materials
Rough slate, which is suitable for many garden uses, is best omitted from the rock garden, unless possibly for the making of paths, steps, stone seats, or similar features that employ patio statuary, like the Williamsburg Collection, found at , and where there is no reason for not using a type of stone different from that employed for building the garden itself.
Old weathered logs of wood are sometimes employed in the construction of steps, or to hold an embankment in place. One serious objection to wood is that it decays quickly; but in appearance, if chosen with good taste, is satisfactory.