Chapter 2
Obvious considerations are that plants with a decided hankering after moisture or shade should be favored in the matter of location, though it is astonishing how adaptive many of them are.
Do not plant the weak next to the strong. Unless you are a gardener of eternal vigilance, the weak will have the worst of it before you realize what a mistake you have made.
Finally, do not forget that planting is not the end; it is only the beginning--of planting. So long as the rock garden exists there will always be planting. Normal mortality will necessitate some, there will be thinning out, and time will suggest additions and more or less rearrangement.
And with the planting goes on the continual care, much of which can be done in the course of the daily walk in the garden, and therefore the loss of time will not be felt. Water in case of a real drought, but use a sprinkler, and do not stop until the ground has been soaked to a depth of a few inches. Mere surface watering is bad enough in the ordinary garden; in a rock garden it is a fatal error, as the growth of roots near the top of the soil leaves the plants in no condition to stand the full force of the summer sun.
Go over the garden thoroughly once a year and all the time keep a sharp lookout for weeds. If the soil is heavy, top-dress with grit in the fall. Grit is good for rock plants. Stone chips placed around a plant will prevent too much dampness lodging about the collar in winter. Watch out for weak spots after very heavy rains.
PLANTS FOR A ROCK GARDEN
So many plants are suitable for a rock garden that the range of choice is bewildering. In this, as in the laying out of the garden, advisability takes precedence over pure personal desire, though, very fortunately, it is often not difficult to make the two go hand in hand; a little intelligent thought helps a lot.
To the beginner, no better advice can be given than that which applies to the picking out of the rocks--use the material which is close at hand. This is not, by any means, a mere suggestion to follow the lines of least resistance. It is far more. In the first place, there is always an endless amount of beautiful and suitable plant life to be had without going far afield. Then again, natural harmonious effects in your immediate neighborhood are pretty sure to be appropriate to your grounds. Finally, you can see for yourself how things grow, and as for the hardiness of plants, you have it already tested for you. This refers not alone to the natural conditions; there is a second wide field in the gardens--the hardy gardens--of others, where you can at once choose from the many and learn whether certain plants are too tender or require too much care for your use.
So far as plants native to the immediate neighborhood are concerned, their value to the rock garden of the average person with limited time, who is not obsessed with the idea of growing the rare and curious, cannot be overestimated. And they are so many; more than most realize, and often of an individual beauty not always appreciated in the bewildering profusion of the wild but plainly apparent when an individual, or a little group, is open to close study in a rock garden. Do not make the rather common mistake of thinking that they are too familiar to be interesting; they are never likely to be. And, honestly, can you say in your heart that they are?
For a Connecticut rock garden the Greek valerian (_Polemonium reptans_) must be purchased, unless a neighbor can spare some from his collection of old-fashioned flowers; there it belongs in that category. But why should you of Minnesota or Missouri deny so beautiful a flower a place in your rock garden, simply because you have only to go to the woods for it? The English enthusiast brings home primroses from the Himalayas, gentians from the Swiss Alps, and _Dryas Drummondi_ from the Canadian Rockies for his rock garden, but he does not fail to take advantage of some of the common things near-by--even the "pale primrose" and the cowslip.
From ferns alone, or from only plants of shrubby growth, a most beautiful native rock garden may be made. And adding small flowering plants, or excluding all else, there are limitless opportunities. It goes without saying that A's rock garden in Maine will not be like B's in Louisiana; but there is no law compelling it to be.
Among the common wild flowers of the East that take on unexpected new beauty when transferred to the rock garden are the celandine (_Chelidonium majus_), strawberry (_Fragaria Virginica_), cranesbill (_Geranium maculatum_), toadflax (_Linaria vulgaris_), orange hawkweed (_Hieracium auranticum_), herb Robert (_Geranium Robertianum_), coltsfoot (_Tussilago Farfara_), Solomon's seal (_Polygonatum biflorum_), foam flower (_Tiarella cordifolia_), bloodroot (_Sanguinaria Canadensis_), and some of the violets. These are but a few names, and random ones at that. Some of them, the coltsfoot, cranesbill, celandine, and toadflax, spread too rapidly, but by careful watching and not allowing the seed to ripen, they may be kept within bounds. There are many such plants that will take all the room in sight if they are allowed to, and they must be watched closely, or else discarded altogether. Some of them answer a good purpose by giving the rock garden a quick start, after which they may easily be reduced or thrown out altogether. There need be no compunction about discarding. Certain plants, like certain friends, you enjoy having for a visit, but do not care to see remain forever and a day.
Annuals as a class are not desirable for the rock garden; for one thing, the care of renewal is too great. Biennials are almost as much care, but in each case there will always be exceptions that are a matter of individual preference. Few, for example, would have the heart to reject the dainty little purple toadflax of Switzerland (_Linaria alpina_), just because it is a biennial. The main dependence, however, must be placed on perennials--the plants that, barring accidents, last indefinitely. These should be mostly species; if horticultural, do not use the bizarre--Darwin tulips, for example, or the Madame Chereau iris. Nor, with rare exceptions, should double flowers be used. A double daffodil looks horribly out of place, while the double white rock cress (_Arabis albida_) will pass.
The easy rock garden plants, where the material is not taken from the wild, are to be found in most of the large hardy gardens of the East. Some of them are natives of Europe or Asia, and more than is commonly suspected are at home in other parts of the United States. Among the best of these for carpets of bloom are _Phlox subulata_, _Phlox am[oe]na_, _Aubrietia deltoidea_, maiden pink (_Dianthus deltoides_), blue bugle (_Ajuga Genevensis_), white bugle (_Ajuga reptans_), woolly chickweed (_Cerastium tomentosum_), creeping thyme (_Thymus serpyllum_), dwarf speedwell (_Veronica repens_), _Saponaria ocymoides_, alpine mint (_Calamintha alpina_), and pink, white, and yellow stonecrops (sedum). All of them fairly hug the ground. There are other plants that form a carpet of foliage, but the flower stalks rise higher. These include white rock cress (_Arabis albida_), the permissible double buttercup (_Ranunculus acris fl. pl._), the also permissible double German catchfly (_Lychnis viscaria_), another double flower, "fair maids of France" (_Ranunculus aconitifolius_), Carpathian bellflower (_Campanula Carpatica_), grass pink (_Dianthus plumarius_), _Iris pumila_, crested iris (_Iris cristata_), Christmas rose (_Helleborus niger_), _Phlox divaricata_, _Phlox ovata_, _Phlox repens_, foam flower (_Tiarella cordifolia_), _Veronica incana_, _Alyssum saxatile_, _Saxifraga cordifolia_, and various avens (geum).
Several of the primulas give a like effect if the planting is close--as it should be in a pocket. The best are the English primrose (_Primula vulgaris_), cowslip (_P. veris_), oxlip (_P. elatior_), bird's eye (_P. farinosa_), yellow auricula (_P. auricula_), _P. denticulata_, and _P. Cortusoides_. Similarly, spring bulbs may be employed; plant them, for the most part, under a ground cover so that the soil will not show when they die down. Of the tulips, single ones of the early and cottage types may be used, if in a solid color, but most to be preferred are the species, such as the sweet yellow (Florentine) tulip of Southern Europe and the little lady tulip (_Tulipa Clusiana_). Crocuses are also best in type forms, and the small, single, yellow trumpet kinds are the finest daffodil material. Single white or blue hyacinths may be used, but better than the stiff spikes of bloom of new bulbs will be the looser clusters of bulbs that have begun to "run out" in the border. Other valuable bulbs are the snowdrop, _Scilla Sibirica_, glory-of-the-snow (_Chionodoxa Luciliæ_), guinea-hen flower (_Fritillaria Meleagris_), grape hyacinth (_Muscari botryoides_), _Triteleia uniflora_, _Allium Moly_, and the wood and Spanish hyacinths (_Scilla nutans_ and _campanulata_).
Taller plants that may be worked in, oftentimes best with only a single specimen or small clump, are autumn aconite (_Aconitum autumnale_), _Yucca filamentosa_, leopard's bane (doronicum), single peonies (either herbaceous or tree), German, Japanese, and Siberian iris, as well as the yellow flag (_Iris pseudacorus_), single columbines, _Anemone Japonica_, _Hemerocallis flava_, _Sedum spectabile_, _Dielytra spectabile_, _Dielytra formosa_, Jacob's ladder (_Polemonium Richardsonii_), fraxinella, _Anthemis tinctoria_, single _Campanula persicifolia_, _Campanula rapunculoides_, _Campanula glomerata_, globe flower (trollius), snapdragon (antirrhinum), platycodon, lavender (where it is proven hardy), and musk mallow (_Malva moschata_).
Of the lilies, _Lilium Philadelphicum_, _L. elegans_, _L. speciosum_, and _L. longiflorum_ are all desirable, and they thrive in partial shade, though in Japan _L. elegans_ will be found standing out from the rocks in full sunshine. For peering over into the rock garden, rather than being placed in it, _L. Canadense_, _L. tigrinum_, and _L. superbum_ are recommended.
The pick of the low shrubs are the charming _Daphne cneorum_, which flourishes better for being lifted above the ordinary garden level, and _Azalea am[oe]na_. The latter, however, should be so placed that its trying solferino does not make a bad color clash. Rhododendrons and mountain laurel fringe a rock garden well, and with one trailing juniper (_Juniperus procumbens_) will provide a great deal of the refreshing winter green.
Single roses, the species, fit in well where there is room for them. Good ones are _R. setigera_, _R. rubiginosa_, _R. Wichuraiana_, all rampant, and the low _R. blanda_. The roses would better be at or near the entrance or exit, or far enough above the rock work not to ramble over small plants.
The plants in this list cover all seasons and vary somewhat in their soil and moisture requirements. But the variation is nothing beyond the ordinary garden knowledge. Most will do better if their preferences are considered, but none is apt to perish with average care.
Alpines, as a class, would better be left to the amateur with the time, money, and disposition to specialize. Most of them take kindly to being transferred from a mile or more up in the air to sea level; the edelweiss, for one, grows here readily from seed, and the exquisitely beautiful _Gentiana acaulis_ thrives in American rock gardens. But, on the whole, alpines do not do as well here as in England, where the summer climate is not so hard on them. When they flourish here, it is at the cost of a great amount of professional care.
THE WALL GARDEN
A wall garden is a perpendicular rock garden. But whereas a rock garden is of all things irregular, a wall garden has regularity. The wall need not be a straight line; it is better that one end should describe a curve, and rocks at the base may give it further irregularity. Yet it can never quite lose the air of man's handiwork. The prime object of the gardening on it is to reduce this air to a minimum.
The way to make a wall garden is to build a dry wall of rough stones--that is, a wall without mortar. Instead use soil and pack it tight in every crevice as well as behind the stones, which should be tilted back a little to carry water into the soil. This tilting may be accomplished with small stone wedges. The best kind is a five-foot retaining wall, as there is then a good body of soil behind to which the roots can reach out through the crevices. But a double-faced wall may be made, if the situation demands it, by constructing parallel lines of stones and filling in solidly with soil.
Although the face of the wall in either case may be strictly perpendicular, it is better that each layer should recede a bit. Construct it after the manner of the rock garden, laying the stones so that the top will be level, or approximately so.
In planting also, follow the same rules. It is better to plant as the work progresses. Either plants or seed may be used. If it is seed, press carefully into the soil in the front of the crevices. Small seed may be mixed in thin mud and this plastered on the soil. For a tiny crevice make a pill of the mixture.
The range of reliable plants that do not call for special care is not great so far as the crevices are concerned. All the stonecrops, the house leeks, _Arabis albida_, red valerian (_Centranthus ruber_), aubrietia, _Alyssum saxatile_, snapdragon, wallflower (_Cheiranthus Cheiri_), Kenilworth ivy, _Viola tricolor_, _Dianthus plumarius_, and _Dianthus deltoides_ are all very serviceable. Behind the wall, at the top, a strip of earth should be left and there a wider variety of plants can be grown. Single Marguerite carnations and grass pinks will form a sort of cascade of foliage and bloom there if planted close to the wall or in the crevices of the top, and a similar effect, but much bolder, can be created with the perennial pea (_Lathyrus latifolius_).
If the dry wall is already made, the crevices can be plugged with soil if care and patience are used. Even a cemented wall is not hopeless; here and there the mortar can be chiseled out and an occasional small stone should be removed.
A wall garden has these advantages over a rock garden; it is more easily constructed, it is of practical use, and it is sometimes a possibility where the other is not.
WATER AND BOG GARDENS
Neither the water nor the bog garden is dependent on rocks. Either or both, however, may just as well be an adjunct of the rock garden. They solve the wet spot problem admirably, permit the culture of native water lilies, orchids, and numerous other beautiful plants, and certainly contribute their share of picturesqueness. If water is lacking, it may often be introduced at little expense.
In most cases it will be found that some cement construction is necessary, but not a bit of it should show. This is easily managed by building a cement shoulder on the sides of the pool or stream a little below what will be the level of the water, and then setting rough stones on that. A cement bottom for shallow water may be disguised by imbedding pebbles and small stones in the cement before it sets.
Dispose the rocks very irregularly, but they may be so few as to be mere notes. Avoid stagnant water, and if mosquitoes are feared introduce some goldfish. They like mosquito larvæ.
Water lilies and sagittaria--one plant will do if the pool is small--in the water and near it, but not in standing water, Japanese iris, yellow flag, globe flower, and _Lythrum roseum_ are good selections. Forget-me-not is one of the finest plants for the banks. Use the perennial kind (_Myosotis palustris semperflorens_).
The bog garden simply reproduces bog conditions. As a rock garden adjunct it may be a small spot with the perpetually moist and moss-covered soil in which the native cypripediums and pitcher plants flourish. Eighteen or twenty inches of suitable soil, a mixture of leaf mold, peat, and loam, in which has been stirred some sand and gravel, must be provided. If an artificial bog, the bottom may be made of cement or puddled clay.
* * * * *
[Transcriber's Note: Two oe ligatures in the original book have been rendered as [oe]. A spelling error in the original has also been corrected: "Polemonicum" to "Polemonium" (Page 41: "... Jacob's ladder (_Polemonium Richardsonii_) ...") Italics are rendered as _underscores_.]
End of Project Gutenberg's Making A Rock Garden, by Henry Sherman Adams