How to Make a Rock Garden

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How to Make a Rock Garden

When rock garden was introduced to the United States from England in the Iwo's, itsoon became a craze. Those early rock gardenswere developed in the English tradition, withemphasis on the beauty of composition of bothrocks and plants, but after a while many ofthese man-made gardens became an ugly con-glomeration of rocks and stones. Soon, theywere overdone, followed by a decline, but after World War II, a fresh approach was introducedin the Japanese style, with stress on opennessand simplicity.

A rock garden may be defined as an out-cropping of rocks—natural or devised—wherealpine plants from the mountainous regions ofthe world are grown. Usually it is on a slope,and although the plants chosen generally comefrom rocky places, usually at high elevations,many are simply low-growing perennials,annuals, bulbs, and shrubs that fit into thecategory.

Many gardeners are fortunate in havingnatural rock gardens, where their choicetreasures are brought in and arranged in anartistic manner. In other instances, they areconstructed with rocks—and boulders—thathave been hauled in. This requires great skill,and the best are the the result of the skillfulexecution of outstanding landscape architectsand plantsrnen. Unless well done, a rock gardencan be an eyesore, nothing more than a merepile of rocks among which plants are set andoften allowed to grow rampant.

The natural rock garden is characterized bylight, poor, gravelly, well-drained soil. In theconstructed garden, this kind of soil is essential.It provides the kind of medium in which mostof these plants survive. A heavy soil in winterbecomes water logged. By remaining too damp,plants tend to rot, especially where winter rainsare heavy. A too-rich soil promotes lush, softgrowth that likewise is inclined to becomewinter-killed.

The artificial rock garden should be con-structed with the proper growing conditions inorder to display plants that generally cannot begrown elsewhere. It is intended for alpine plants,which are found growing wild on mountainsbetween the tree line and the lower limits ofsnow. The rocks not only show off the plants tobest advantage, but perform other importantfunctions. They help to keep the soil cool and toconduct moisture to the plant roots. Excessivemoisture through evaporation is prevented, andthe soil is held by them in place. Even when allthese conditions are provided, the rock gardenmay not fare well, but for another reason. It hasto do with the length of the growing season,usually varying with that of the natural habitatof the plants. That is why the careful selection of plants is of great iraincrtance.

The well-designed rock garden, especially iflarge, will be represented by many differentkinds of topographical areas. It may have arocky hillside and a steep slope. It may displaya low plain, a hidden valley, a bog, a brook orstream, and a cuiet pool, as commonly foundin nature. At some point, it may even possess ahigh and windy mountain peak where fewplants grow.

In extensive stretches, larger, bolder plants maybe used. The smaller the rock garden, the smallerthe plants should be. Most rock plants are undera foot in height when full grown, but dwarfshrubs, may be up to 3 feet. Although alpineand rock plants are usually selected, othersqualify if their size and height are right. Theymay be mat-forming or spreading and may comefrom meadows, woods, prairies or bogs. Manythat are typical rock plants are often grown inborders with other flowers, among them Arabis,Aubrieta, Gold-dust, Cerastium, Hardy randy-tuft, Dwarf Iris, Ground Phlox, Prillium, andEpimedium. To these can be added a widevariety of small bulbs and low annuals, likeSweet Alyssum, Lobelia and dwarf Frenchmarigolds.

The classical rock garden, with its need forhand and knee labor by skilled gardeners, hasbecome a thing of the past. It was intended tocopy nature and to display many interesting andunusual plants, some of them rare. Today's rockgardens have changed to meet the needs of thetimes. Simplicity and ease of maintenance is thekeynote. Yet there are many lovely compositionsthat have resulted from this new concept whichhave combined the best and most practicalelements of the British and the Japanese, the 2styles that have helped to mold the contempor-ary- rock garden of today.

As with other forms of gardening, certainbasic principles apply—scale, proportion, bal-ance and good design, which includes a pleasingarrangement of the various parts into anharmonious whole. Most of all, it is originalityand imagination that count.

Location

The site of the rock garden is of primeimportance. if there is a natural outcropping ofrocks, such as found in New England, theAppalachians, the Rockies and other moun-tainous areas of the country, then select it, sincethere is nothing more beautiful than an arrange-ment of rocks placed in position by the forcesof nature.

Most home owners, however, are notfortunate enough to possess such a setup. Ifan artificial rock garden is to be constructed,then look for a bank or a slope. Even at that, it plants in such locations, but they know theneeds of the various kinds in order to keep th-Z:7in top shape. In some cases, it may mean someform of winter protection. These garde:he-ie.avoid plants that require shade during thehottest part of the day, or find cool, shady nooksfor them in crevices of large rocks or boulders.On south-facing slopes, small trees that cas:light or limited shade, as birches, crabapples.and flowering dogwoods, arc planted to cut on:the intensity of the baking sun.

In any case, allow for full sun for at least partof the day. Yet charming rock gardens can beestablished on natural outcroppings where largetrees, too precious to cut down, exist on theproperty. In such instances, the rock gardenwill not be gay and colorful in spring and earlysummer, but it can impart simple charm and afeeling of coolness with hostas, Lily-of-the-valley, epirnediums, Ajuga, trilliums, Bloodroot.yellow lady's slippers, ferns, and low yews andazaleas. In summer, bits of color can be addedwith Coleus., Patient Plant, tuberous begonias,Madagascar Periwinkle, fancy-leaved caladiums.Thunbergii. In early spring, before trees dontheir leaves, miniature bulbs and speciesdaffodils and tulips will unfold their prettyflowers.

Design

Before starting to build, whether you willplant around existing rocks or start from thebeginning, make sketches on paper. A rockgarden, like any other type of garden, is basedon principles of design. If it is large, it will needpaths and walks, or at least stepping stones.and the paths should be of a winding, informalnature. Straight, rigid lines are not appropriate.Paths not only make delightful wandering, butmake it possible to reach the plants in order tocare for them. Unless comprised of stones, theyshould be covered with natural material, likepine needles, tanbark, shredded tree bark, orstone chips or pebbles. Be certain that thesepaths blend in with the surrounding plants.

If working with a steep slope, it will benecessary to make several terraces to hold backthe soil. Areas can be leveled off every 2 feet before rocks are arranged on them. in manycases, this can add to the appeal of the rockgarden, adding interest because of the levelvariations.

it is also well to jot down on paper thepositions of several plants. At this point, it isadvisable to get to know their growth habits.Some, like Arabis and Ajuga, are aggressive b.;nature, so try to place them between large TOCI:where their spreading nature can be checked.

Rock Garden

can be built on level ground, although it takesfar greater ingenuity to make it look as if it hasalways been there. Some of the great rockgardens of the world, often found in botanicgardens, are made, and are so artfully executedthat they have every feeling of being natural.

When choosing the location, look for a spotthat receives abundant sunshine, away from theshade of large trees which cut out the sunlightand rob plants of precious nourishment andneeded moisture. When dealing with a slope,this is not always possible, but sometimes, thereis a choice. Keep away from artificial surround-ings, since a rock garden is essentially a casual,informal type of garden expression that shouldharmonize with its immediate surroundings.Avoid as backgrounds high, austere wails,porches or the facades of houses, drivewaysand sidewalks, and a strictly formal garden,with clipped hedges and plants arranged ingeometric patterns.

Exposure should also be taken into considera-tion. Rock garden and alpine plants are sunloving, although this does not mean fullexposure to the all-day sun. m some instances,specially if the shone faces south, this can beharmful in the case of winter sun and winds.One that faces east is considered ideal, butnortheast, west and northwest are also excellent.When dealing with alpines from high mountaintops, north exposure, open to the sky, withoutany interference from trees, is recommended.This is because these small plants are covered,in their native haunts, by a thick blanket ofsnow all winter, and are not exposed to the sunor biting winds.

Southern exposures, particularly in the caseof more rampant plants such as Ground Phlox,Aubrieta, Arabis, Gold-dust, and Dwarf Iris,are not to be neglected altogether. Many out-standing rock garden specialists have thriving sides of reeks where they present a glorioussight when in full flower. Less vigorous kinds,like small aipines, should be placed in narrowcrevices where they will not be overpowered.

When designing the rock garden, avoidpockets where water collects, since good drain-age is essential for success. Secure rocks well byplacing them deeply. Any that are loose cancause damage when accidentally walked on. Lookfor rocks that are native to the region; sincethey fit into the seP-ing better. Weathered rockof any kind is good, but obtain stones that areirregular and asymmetrical and dark in color-ing. Rounded stones are bad because they donot look natural.

Select rocks of different sizes, but avoid theuse of too many. A rock garden is not a collec-tion of rocks, but a collection of plants arrangedaround carefully selected and placed rocks andstones. Few types of gardening are more easyto overdo than this. A mountain of rockspresents a jarring note that not even a healthygrouping of flowering plants can ameliorate.

Soil

In a way, soil and construction go hand inhand. If soil is not the right kind, it can bespecially prepared to meet the needs of theplants. In the case of existing rocks, poor soilwill have to be scooped out and replaced withthe proper mixture.

Most rock garden plants are not fussy aboutsoil, and will grow in almost any kind, providedthere is good drainage. Some plants require anacid soil, others prefer one that is alkaline. Yetmost thrive in soil that ranges between pH6and pl-18. A thin, porous one is best, more so insections of the country where rainfall is heavy.

Where droughts prevail during the growingseason, the soil should be heavier and moremoisture-retentive to meet the needs of plants.In this case, it should be prepared beforehandwith humus. Other aids consist of using mulchesof fine gravel or stone chips to hold in the mois-ture. These will also help to prevent weeds fromtaking over.

A simple preparation consists of equal partssoil, coarse sand, and peat moss, leaf mold orcompost. Another combines equal parts loam,leaf mold, peat moss, sand and fine gravel.Since most rock garden plants are lime-loving,add agricultural lime. Unless soil is very acid, aheavy sprinkling will do. Bone meal or superphosphate, slow-acting phosphoric fertilizers,can be added at the recommended amounts.Some rock plants do not need it, but others likeDianthus, campanulas and daphnes appreciateit.

If scooping out soil in pockets and betweencrevices in natural rock outcroppings, dig to a

depth of about a foot, where this is possible.Place a layer of stones, pebbles, or pieces ofbroken bricks at the bottom. Then add a layerof coarse sand or gravel before placing the soilon top. Wash each layer with the hose to make itsettle firmly and eliminate air pockets.

Construction

Constructing the rock garden is not the easiesttask. It is advisable to do considerable readingbeforehand and, where possible, employ theservices of a qualified landscape architect. Ineither instance, observe and study rock forma-tions in nature. The idea is not to copy them, butto receive inspiration and understand how theycomprise a harmonious whole. Small rock cartbe lifted easily, but with larger ones you will needsuitable tools. One or two crowbars will beamong the handiest.

If proceeding on your own, first bring togetherthe rocks to be used. Unless you have masteredyour design so it is clearly in your mind, keepthe plan sketched on a piece of paper close athand.

Start to work at the lowest point. After plac-ing a layer of drainage material at the bottom,add about A of the prepared soil in that par-ticular spot, leaving the rest to spread aroundthe rocks when in their final position. Generallyspeaking, keep the largest rocks for the base. Insome instances, existing soil will have to beremoved to make room for these boulders.Place them on their broadest bases, makingcertain they are secure. When completed, morethan half of each rock should be under thesurface of the ground. Arrange each so it leanstoward the soil in order to catch rain water.Most of the rocks will have lo be concentrated insteep places to hold back the soil. Use fewerwhere the grade is less abrupt, and allow forlarge levels where quantities of vigorous rockplants will be permitted to spill over the sides.Here and there small rocks can be used to givethe impression that they have tumbled down. Thekey of the successful rock garden is to make itlook as natural as possible, rather than man-made.

Before setting each rock in its permanentposition, stand back to see how it looks. Turn itaround a few times, and you will discover that,what was previously the bottom, may well bethe top. At this stage, it is easier to make changes.

When completed, and before you start toplant, let the rock garden rest for a few days.Up to this point, you have been too close to itand need to get away from it. You will have theopportunity to stand bacit and see the rockgarden from several different angles at varioustimes of the day, under divergent condition ofsunlight and shadows. Strive for unity, harmony, with pot grown plants, as is often the case now-adays, you can do the work any time during thegrowing season, if water is available. Set outplants when soil is moist and crumbly. Avoid avery wet soil, which tends to cake and pack theroots, cutting down on the air supply.

When planting, firm the soil around the roots.You will have to take special precaution to getrid of air between rock crevices. Work slowly,ramming the soil as you proceed. Where spacepermits, use 3 or more specimens of the samekind in order to produce a broad splash offoliage and color. In small crevices and nooksuse small alpines. They look more endearing,and are protected from vociferous neighbors bysurrounding rocks. Dwarf types, as saxifrages,primulas,aubrietas, and small achilleas, can bespaced 6-8 in. apart. More spreading thymes,ecrostiums and Ground Phlox will need atleast a foot.

Always strive for informality in the rockgarden. A formal rock garden does not exist innature. Plant singly or in clumps, but never inrows. Allow an occasional plant to stray hereand there. Tuck one in a sheltered crevice,another in a narrow opening between stones.Always permit some to cascade, for they imparta special charm. Bring together beguiling foliagetextures and patterns, not so difficult if you putyour imagination to play.

Maintenance

On the whole, the rock garden requires littlecare, no hoeing or cultivating and very littleweeding, once weeds are pulled up and thickmulches are applied. A minimum of feeding isneeded, since a too-rich diet will promote lushgrowth that tends to rot or winterkill.

Even so, like any other form of gardening,general upkeep must be practiced if the rockgarden is to look its best. It can quickly becomean eyesore.

10 the early spring, after winter covers areremoved, gradually, according to the dictatesof the weather, check plants to see if they needto be firmed back. Winter thawing and heavingwill loosen them, but with the hands or feet thisis easily done when soil is moist, but not wet.Some plants may require replanf;r.g if they havebeen pushed out of the soil too much.

A light scattering of a high phosphoric fertilizer, such as 5-to-5, can be spread on the surfaceof the soil and scratched in with a weeder where this is permissible, if it does not interfere with plant roots. still, top dress the rock garden,using a mixture of 3 parts garden soil, r partleaf mold or peat moss, and f part coarse sand.To this add a 6-in. pot of bone meal to eachwheelbarrow of prepared soil.

Planting

Planting the rock garden requires a specialkind of skill. First, become acquainted with thedifferent kinds of plants. Some are shy, othersare vigorous. Some arc very hardy, others willneed winter protection. It is important to knowthe forms and growth habits of each, as theyvary to include the prostrate, rounded, spreadingand upright forms.

As a beginner, start with some of the easierkinds, but this does not imply a limited variety.En fact, much of the interest in the rock gardenstems from its varied number of plants. Asyou become familiar with these easy kinds,brine in the more difficult. They call for morespecialized attention, but they offer keenerpleasure.

A harmonious composition between rocks andplants is the aim of every rock garden, be itlarge or small. in a way, it is no different fromother forms of gardening. Colors of many rockgarden plants and alpines are bright and vivid—magentas, rose-pinks, golden yellows, orange-reds. Yet this does not mean they cannot bebrought together into a harmonious unit. Wherecolors tend to clash if placed side by side,break them up through the use of white, the"peacemaker." Also in the unobstructed sun-shine, where rock gardens are located, brightcolors go together more easily, as is often seenin tropical gardens.

Early spring is a good time to plant, but betterstill is late summer or early fall when most rockplants are dormant. in spring, they are makingrapid growth to come into bloom. If dealing

Rock Garden

Some rock garden has a low, dry wall, with stones that areloosely set, can be effective as is this one in theDirector's persona! garden in Kew Gardens,England. (Photo by Arnold Arboretum, JamaicaPlain, Mass.)

The wall garden is more difficult to constructthan the rock garden, but the same principlesof design are involved. In it are gown smallplants that abound in crevices and on cliffs, somethat are tufted, some that droop, some thatcling. The early spring is the best time to buildand plant the wall garden, followed by Sept.,which allows enough time for roots to becomefirmly established before the ground freezes.

A wall garden is usually placed in front of abank to hold back the soil behind it. To do thisproperly, it should be solidly built, able to with-stand the pressure exerted by freezing soilbehind it. Properly made, it can be as much astz or 55 ft. high.

As with the rock garden, the largest rocks should be used at the bottom, followed by smaller at the top. Since no mortar will hzused, it is the weight of the stones, one on topthe other, that will keep tne wail firm and makeit last for years. It is preferable to use localstone, although exotic. v;nes can be brought in.The kind of stone to be used will depend, in theend, on the desired effect and the overallsurroundings.

The wall garden inclines backward, so that it is lower at the back than in the front. The individual stone also tilts the same way toward thebank. This way the oar', is held more firmly inposition and the sloping angle permits rain —seep through the crevices to reach the roots the plants as they stretch out to the soil beyonc.

When gathering stones, avoid those that arerounded, and select those that are flat anynarrow. The largest, that will form the founda-tion, need not be below the frost line, but theyshould be secured firmly. Place them in asloping position, that is toward the soil, aboutto in. deep, which is sufficient to provide a firmhold and prevent them from moving after heavyrains or cold winter weather. The width of thebase should be about one-third of the height ofthe wall.

A tall wall makes an effective background for adisplay of vines. (Photo by Arnold Arboretum,Jamaica Plain, Mass.)

The larger the wall, the larger should be thestones. First place a row of the heaviest at thebase, each leaning backward. Then add a fewinches of soil, and it is well to use the speciallyprepared mixture recommenced for rockgardens. Always place about 6 in. of this soil inback of each rock or stone. Pack is in firmly toavoid air pockets, which dry out quickly andusually result in poor growth.

The next layer of rocks will require carefulplacement. Do not rest a rock on top of anotherbut between two, so that its weight is borne bythe rocks and not the soil. Continue in this manner all the way to the top. Always placeeachrock in a horizontal position. When completed,the weight will be carried by the rocks, andthere will be no vertical crevices in the dry wall.The ideal way to plant is as you go along.After the rocks arc laid and 2 or 3 in. of soil isplaced over them, rest plants in position andspread out the roots, covering them with 2 or3 in. of the soil preparation. Plant layer at atime, and be certain to tamp the soil carefully.

In many instances, it is not possible to plantas you build. When the construction is com-pleted, scoop out I or 2 trowelfuis of soil from acrevice, insert the roots of the plant, and replaceas much of the soil as possible, pressing itfirmly. Use smaller plants than you would bythe other method, but also be prepared toexpect some losses. Water and keep moist untilplants are established.

Seeds can be sown in the wail garden in thespring. Mix the seed with moist sandy loam andpress into the openings and crevices. A smallpiece of moss placed on the soil will help toprevent excessive drying out.

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