Rock Garden
Growing plants in rockgardens has long been practiced as a form of gardening. When it was introduced to theUnited States from England in the 1900’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 afterWorld War 11, 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 plantsmen. 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 constructed 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 importance.
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 quiet pool, as commonly foundin nature. At some point, it may even possess ahigh and windy mountain peak where fewplants grow.
Inextensive 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 site 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 Candy-tuft, Dwarf Iris, Ground Phlox, Trillium, andEpimediurn. 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 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 walls,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. In some instances,specially if the slope 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 plants in such locations, but they know theneeds of the various kinds in order to keep themin top shape. In some cases, it may mean someform of winter protection. These gardenersavoid 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 castlight or limited shade, as birches, crabapples,and flowering dogwoods, are planted to cut outthe 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. Sc 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, epimediums, Ajuga, trilliums, Bloodroot,yellow lady’s slippers, ferns, and low yews andazaleas. In summer, bits of color can be addedwith Coleus, Patient Plod, 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 snake delightful wandering, butmake it possible to reach the plants in order tocare for thern. 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 or 3feet 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. Al this point, it isadvisable to get to know their growth habits.Some, like Arabis and Ajuga, are aggressive bynature, so try to place them between large rockswhere their spreading nature can be checked.On the other hand, trailers, like Gold-dust orGround Phlox, can be allowed to trail over the sides of rocks where they present a glorioussight when in full flower. Less vigorous kinds,like small alpines, 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 setting 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 pH8. 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 canbe 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 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 to 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 assay from it. You will have theopportunity to stand back and see the rockgarden from several different angles at varioustimes of the day, under divergent condition ofsunlight and shadows. Strive for unity, harmony, and balance, and try to capture the rhythm andthe feeling of a natural ledge, the kind you haveoften admired in nature.
Planting
Planting the rock garden requires a specialkind of skill. First, become acquainted with thedifferent kinds of plants. Some are shy, othersare vigorous. Some are 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.In fact, much of the interest in the rock gardenstems from its varied number of plants. Asyou become familiar with these easy kinds,bring 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 sooty, it is no different fromother forms of gardening. Colors of many rockgarden plants and alpines are bright and vivid‚Äîmagentas, 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
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,cerastiums 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 becomeeyesore.
In the early spring, after winter covers areremoved, gradually, according to the dictatesof the vveather, 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 replanting if they havebeen pushed out of the soil too much.
A light scattering of a high phosphoric ferti-lizer, such as 5-to-5, can be spread on the surfaceof the soil and scratched in with a weeder wherethis is permissible, if it does not interfere withplant roots. Better still, topdress the rock garden,using a mixture of 3 parts garden soil, I partleaf mold or peat moss, and 5 part coarse sand.To this add a 6-in. pot of bone meal to eachwheelbarrow of prepared soil.
In spring, you will want to check each plant caretully to see how it is doing. There may bedead growth in need of removal. Some largeplants, not pruned the previous summer, mayneed cutting back, but do this carefully in ordernot to cut down on the display of bloom. Ifsome plants have died, remove them and replacewith others. Large specimens can be divided, butit is better to wait until after flowering is pastand plants go into their semi-dormant period.In established rock gardens, plants in crevicesmay appear weak. Most likely they have exhaust-ed the soil, so lift them and provide a freshmixture, well fortified with organic matter andsome fertilizer. Their revival will be amazing.If these are to be separated, retain the outershoots, which are the most vigorous.
Many rock plants are drought-resistant, butduring prolonged dry periods they will needdeep watering. Allow the sprinkler to run for along time or use watering wands or soakers thatpermit the water to ooze out slowly. If wateringis too quick much of the water will roll assay andbe of little aid to the rock garden.
Through the summer months, some handweeding will be needed. For this, a dandelionweeder is excellent or use a long-handle cultiva-tor with 2 prongs. A well-designed and builtrock garden is one that enables the gardener toreach any part without stepping on plants.Paths, walks, and large, flat rock surfaces makethis possible.
Trim back rampant growers in late summer,such kinds as Gold Alyssum and Arabis. Someplants can be sheared, but try to keep this un-even. If each plant is clipped into a neat,rounded mound, it will look unnatural. Allowsome to trail over rocks or the ground providedthey do not infringe on their less aggressiveneighbors. To keep up appearances, keep re-moving dead flower heads and stalks as much aspossible. This will also prevent seed formation(except where wanted), which can be exhaustingto plants.
In Aug. or early Sept., lift, divide, and replantpieces of those in need of it. Give fresh soilmixtures and mulch with gravel or anothermaterial, the kind you are in habit of using.Extra plants may be given to friends andneighbors or planted in the garden in out of themay places. They may come in handy later on.
Winter Mulches
Strangely enough, in spite of their extremehardiness, many rock garden and alpine plantsrequire some form of a mulch to protect themduring the winter. Where they grow naturally onmountain slopes and tops, they are covered mostof the winter by a thick blanket of snow, whichprovides perfect insulation against wind andsun. The greatest winter enemy of rock plants is
the possibility of building up excessive moisture,and it is dampness, if it persists, that causesfoliage to mat and rot. Alternate thawing andheaving present another problem, and this iseliminated by a thick, airy blanket in winter.Where snowfall is heavy and lasts all winter,this is less apt to occur, and mulching is not sonecessary.
Them are some plants with foliage that matwhich do not require a mulch, of which Arabisis an outstanding example. Those that die to theground, like Fringed Bleeding Heart andEpimedium, come through the best, but thosewith woolly, mat-forming rosettes should notbe overlooked.
A good mulch is light, airy and attractive. Itshould not hold too much moisture or tend todecay. Evergreen branches, like unused Christ-mas trees or branches of White Pine or othernative evergreens (more readily available) arehighly recommended because they allow air topass through. At the same time, they are goodlooking.
Salt or marsh hay and straw are equally good.They are easily worked in among the stones orsmall shrubs. Cranberry branches will do thesame job. If you are going to use leaves, cutbranches of Oak with the leaves attached, theymake a desirable winter cover, but keep awayfrom maple, which flatten when wet and causeplants to smother. The time to apply thesecovers is in early winter after the ground hasfrozen. Remove gradually in the early springafter the snow has melted, when the frost is outof the ground, and when temperatures will stayabove freezing.
Some of the more unusual and difficult-to-grow plants that are subject to injury or killingfrom excessive dampness will require a collar ofstone chips. It will lift leaves above the ground,in the case of evergreen or nearly evergreenkinds, and aid in drawing the moisture awayfrom the crowns. With some, a mixture of peatmoss, sand, and stone chips may be worked inthe soil around the tops. In the late fall, afterthe first freeze, a small alpine often tends to belifted out of the ground a few inches. Press backwith the foot or a stick or trowel and then mulch.The most prized plants may even have to belifted and placed in the cold frame for the winter.
The Wall Garden
The wall garden can be a charming addition toany garden. More difficult to build than therock garden, it presents a mood and character ofits own. The major advantage is that it enablesthe owner of a small place to grow rock gardenand alpine plants. It can also form the boundaryof the sunken garden. In this case, it shouldrarely be more than 3 ft. high. The wall garden is more difficult to constructthan the rock garden, but the same principlesof design are involved. In it are grown 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 asto or 15 ft. high.
As with the rock garden, the largest rocksshould be used at the bottom, followed by smaller at the top. Since no mortar will beused, it is the weight of the stones, on top ofthe other, that will keep the wall firm and makeit last for years. It is preferable to use localstone, although exotic kinds 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 itis lower at the back than in the front. Eachindividual stone also tilts backward toward thebank. This way the bank is held more firmly inposition and the sloping angle permits rain toseep through the crevices to reach the roots ofthe plants as they stretch out to the soil beyond.When gathering stones, avoid those that arerounded, and select those that are flat andnarrow. 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. 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 recommended for rockgardens. Always place about 6 in. of this soil inback of each rock or stone. Pack it 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 are 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 t la, 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 t or 2 trowelfuls 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 wall 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.
Kinds of Plants
Plants for rock gardens consist mainly of low-growing perennials, along with dwarf kinds ofannuals that are grown to introducecolorduringthe summer months. Hardiness varies with thesection of the country, but for the most partrock and alpine plants are tough, able to with-stand considerable winter cold. Small shrubs,usually under 2 ft. high, fit well into the picture,and are planted to add height, color in the caseof flowering kinds, green from evergreens inwinter, and picturesqueness of form and branch-ing habit. In very large rock gardens some thatgrow as much as 3 ft. tall are worthy of con-sideration.
The following are a few of the most suitable,easy to grow, and readily available that thebeginning gardener can use. Local nurseriesoffer a wide variety, and these can be chosen onthe basis of appeal. There are, for example,many kinds of low-growing azaleas, but becausetheir hardiness varies, they are best purchasedfrom nearby nurseries.
Arctostaphylos uva-ursi (Bearberry)—trailingevergreen, with small glossy leaves, that turnpurplish in winter. Good in poor, sandy soiland loot places. Small white-pink flowersfollowed by red fruits. Very hardy.
Berberis wilsoniae (Wilson Barberry)—alow, spreading, almost prostrate barberry, withsmall, spiny, pale green leaves that turn brightred in autumn.
Cotoneaster horizontalis (Rock Spray Cotone-astcr)—flat shrub that spreads in horizontalmanner, with small, shiny leaves and red berries in the fall. C. microphylla (Small-leavedCotoneaster), an evergreen, has the smallestleaves of all. Both these cotoneasters formdense mounds.
Daphne cneorum (Rose Daphne)—sprawlingevergreen, with small, narrow leaves, andclusters of tiny pink flowers known for theirsweet scent. Give full sun, good drainage, andan alkaline soil. Tops require protection fromwinter wind and sun in exposed places in coldregions.
Erica carnea (Spring Heath)—a low, spread-ing evergreen, with fine, needlelike foliage andsmall rosy-pink flowers in early spring.Give sun and light, acid soil. There is a whitevariety, as well as many improved hybrids forthe collector.
Ilex crenata Tonvexa’ (Convex-leavedJapanese Holly) one of the larger-growingshrubs in this category, recommended for largerock gardens. With pruning, its size can becontrolled. It has small, rounded, glossy,dark green leaves. It is evergreen, as are 2dwarf, compact forms, 1. crenata
(Heller Holly) and ‘Kingsville’ which is ex-tremely slow growing.
Juniperus chinensis satgentii (Sargent Juniper)‚Äîa low trailer, 6-10 in. high, with uprightbranchlets. It has silvery-gray leaves, and formsan excellent ground cover where space permits.J. communis depresses (Prostrate Juniper), alsolow growing and spreading, grows to a foot. Itssoft green foliage turns bronzy in winter. J.horizontalis (Creeping Juniper), mat forming,has steel-blue needles. One of its better knownforms is ‘Waukegan’.
Leiophyllutn buxifolium (Box Sand-myrtle)—adwarf evergreen, with small, glossy leaves andclusters of white flowers in May. Recommendedfor sandy, highly acid soils.
Leucothos fontanesiana (L. catesbaei) (Droop-ing Leucothoe)—a large broad-leaved evergreenthat will give emphasis to large rock gardens oroutcroppings. Long, shiny leaves becomepurplish red with cold weather in winter. Smallwhite flowers in drooping clusters appear inspring. Will do well in shade.
Paxistima canbyi (Canby Pachistima)—adense evergreen, with tiny leaves and small darkred flowers. Will form a soft carpet if givenspace. For acid soil in partial shade. Grows afoot high.
Picea glauca ‘Conica’ (Dwarf AlbertaSpruce)‚Äîextremely slow growing, dense, conicalevergreen that will impart accent and focal pointto the rock garden. Requires full sun.
Potemilla fruticosa (Shrubby Cinquefoil)—small, dense, deciduous shrub, with smallleaves and pale yellow flowers that appearconstantly from June to frost. For poor soil in sunny places.
Spiraea bumalda ‘Anthony Waterer’‚Äîanupright shrub, about 2 ft. tall, with showy flatclusters of bright crimson flowers in earlysummer. Will add needed color in sunny sec-tions of larger rock gardens.
Taxes cuspidate ‘Nana’ (Dwarf JapaneseYew)‚Äîlow, spreading, dense Yew, with darkgreen needles that remain lustrous all year-round. It grows in an irregular manner, insun or shade.
The list of rock garden plants is so extensivethat the beginner will want to start out withsome of the easiest, as well as more readilyprocurable. Later, after making a study of rarerkinds, a few new ones can be added each year.The following, however, represent an interest-ing collection that will make a colorful anddependable start.
Achilles tomentosa‚Äîa yarrow, with soft,feathery, woolly leaves and clusters of yellowflowers on 8-in. stalks. Give full sun and poorsoil. Variety ‘Moonlight’ has light yellow flowerheads.
Alyssum alpestre—a creeper, with rough grayleaves and clusters of yellow flowers. Thevigorous A. saxatile, known as Basket-of-Gold, is a sprawling plant, with gray leaves andmasses of dazzling yellow blossoms. A. saxatilecitrinum is a soft yellow form.
Anemone pulsatilla—this is the intriguingEuropean Pasque-flower, admired for itspurple cup-shaped flowers, with their strikingyellow stamens, that appear in early spring. Itsfinely cut leaves are woolly.
Aquilegia canadensis—good in partial shade isthe Wild Columbine, with its quaint red andyellow flowers on hanging stems. It will grow inrock crevices. A. chrysantha, another native, hassoft yellow blossoms with long spurs that con-tinue to appear over a long period of time. It,too, is excellent in light shade.
Arabis caucasica—one of the common,early spring-flowering rock plants that formsdense mats of pure white flowers. There is adouble form that is superior because it lastsmuch longer.
Artneria maritinza—this charming rock plantgrows abundantly along the cliffs in Cornwall,England, the reason it is called sea thrift. Itforms dense tufts of green, and producesheads of bright rose flowers. It is ideal foredging or to grow in openings in pavements.Aubrieta—there are many varieties of thislow-growing perennial that forms carpets ofbright pink, lavender, or violet in early spring.Grow it on banks or along the tops of walls,where it will receive the excellent drainage itneeds.
Calhzna vulgaris—there are many forms of
Heather, an evergreen with fine leaves andmasses of small pink, red, purple or whiteflowers. Give an acid soil, with plenty of sandand peat added. Shear in early spring.
Campanula ccupatica—a low-growing Canter-bury Bell, t ft. tall, with wiry stems of purple orwhite flowers. It is easy to grow in sun or lightshade, and is available in several attractivehybrids. C. portenschlagiana is a dwarf species4-5 in. tall, with violet-blue flowers. It grows withease.
Cerastium tomentosum—another popular rockplant, vigorous and spreading, forming largemats of gray leaves and sheets of white flowers.Cut back after flowering to keep in check.Dianthus deltoides—this is the Maiden Pink ofEngland, a dainty perennial, with tiny glossyleaves and clusters of small, deep pink flowers.More common is D. plumarius, the Scotch Pinkthat is an old favorite. Blue-gray leaves areenlivened with fragrant, toothed, pink flowers inJune. There are many handsome hybrids. Givefull sun and a well-drained soil.
Dicentra eximia—a summer-flowering Bleed-ing Heart, with soft, finely cut leaves andhanging clusters of rose-pink flowers. It thrivesin shade. There is a white form for contrast.Epimedium macranthum—the common nameof this low perennial is Barrenwort. Heart-shaped leaves appear on wiry stems. There areseveral variations of this favorite that are goodground covers in the shade.
Eranthis hyetnalis—Winter Aconite is thecommon name of this small bulb that in everyearly spring unfolds golden-cupped flowers on 3in. stems. The round buds are enveloped byfeathery ruffs. The leaves disappear after theseed ripens.
Gentian septemfida—an easy Gentian that ishappy in moist, well-drained soil in sun or partshade. Clear blue flowers appear in summer.Available are many forms and hybrids.
Gypsophila repens‚Äîa Baby’s-breath thattrails and grows only 6 in. tall. Mounds ofsilvery-gray leaves are enlivened by sprays ofsmall, pink or white flowers.
Heuchera—Coral-bells, good in shade, isappreciated for its airy sprays of small pink,rose, or white flowers. Rounded, scalloped leavesform neat rosettes. There are several hybrids,and all do well in sun or light shade, providedthey have moisture.
lberis sempervirens‚ÄîHardy Candytuft is oneof the most striking of rock garden plants,even when planted in borders. Large plantsbecome sheets of purest white in May. Hybridsinclude ‘Little Gem’ with narrow leaves, and’Snowflake’, medium in height. All are best infull sun.
Iris cristata—this dwarf spring-flowering Iris, only 6 in. tall, produces soft blue andwhite flowers. Creeping plants appreciate lightshade. A white form is choice. I. tectorwn, theRoof Iris of Japan, grows to 8 in. and hasbroader leaves and crested lavender or whiteflowers. Good drainage is important.Lavandula sp.—Lavender is cherished forthe pungent fragrance of the leaves and thespikes of lavender flowers. A small shrub, withgray leaves, it is best in a warm, sunny locationin poor soil. It comes in pink, blue and white.Leontopodium alpinum—this is the famedEdelweiss of Switzerland, an easy alpine, withflowers, composed of bracts, that look likewoolly stars, gray or white, and requires sun.Mitchella repens—the native Partridge-berryis an evergreen, trailing ground cover, withsmall, glossy leaves and white flowers followedby bright red berries.
Phlox divaricata—Blue Phlox is the commonname for this favorite that brightens rockgardens and borders where tulips and pansies aregrown. A creeping plant attaining t ft., it hasnarrow leaves and clusters of pale blue flowers.Sun or shade suit it. P. stolonifera is anotherspecies that is prostrate. Its glossy, roundedleaves provide a perfect foil for the lavenderflowers. It needs a rich, peaty soil. P. subulata isthe proverbial Moss or Ground Phlox, with itsneedle evergreen leaves and dense masses ofmagenta, pink, rose, light blue, lavender, orwhite flowers. Use it to cover a sandy bank.Primula denticulata—a charming Prirnrosethat forms rosettes of bright green leaves androunded flower clusters, lavender in color, inspring. These may be up to to in. in height.Colors also include rose, red, lavender, purpleand white. Provide a moist soil and high shade.P. polyantha is the Common Primrose thatproduces flower clusters in many colors. Givemoisture at all times and keep out of the hotsun.
Saponaria ocymoides—a trailing plant thatdevelops mats of leafy stems and quantities ofpink flowers. Use it to drape over rocks. Itrequires good drainage.
Sedum acre‚Äîa crawling plant that hugs theground with its stems of bright green leaves thatroot as they go along. Yellow flowers last a longtime. It can become a weed unless checked.Grow it in crevices on steps. S. album, alsospreading, has fleshy stems and round leaves.White flowers appear in midsummer. It isrecommended for hot, sunny banks. Trailing isS. spurium, with its flat leaves and pinkishflowers. Variety ‘Dragon’s Blood’ has reddishleaves and deep red blossoms.
Shortia galacifolia—this bears the picturesquename of Oconee Bells. An American native, it isa creeper, with rounded leaves and small, white, bell flowers in spi ing. It needs a peaty sod andpart shade.
Silene acaulis—a winsome plant that growsin dense clumps of small, pointed leaves.Cushion Pink is the common name of thisplant that unfolds solitary pink flowers for aperiod of several weeks.
Teuerium chamaedrys—this member of theMint Family, known as Germander, is a smallshrub, to a foot, with rounded glossy leaves. It isoften grown as a hedge because it withstandstrimming.
Thalictrum kiusianum—a Meadow-rue fromJapan, 3, in. tall, that spreads by stolons sothat it takes over among rocks. Dainty, feathery,pink-lavender flowers are covered by stamens.Thymus serpyllum—this is the Mother-of-thyme, a sprawling, mat-forming plant withtiny leaves and white to purple flowers on up-right stems. Grow it in full sun. T. vulgaris isthe common Thyme, robust and spreading. Ithas small fragrant leaves and lavender flowers.Tiarella cordtfolia—the Foam-flower of ourwoods has deeply lobed, maplelike leaves andspikes of feathery white flowers. It forms a neatground cover in shade.
Veronica incana—a low Veronica, characteriz-ed by light gray leaves and 8-in. spikes of purple-violet flowers in late spring. Give it gooddrainage. V. repens, a creeper an inch or twohigh, sports smooth, glossy leaves and pale blueflowers, forming a perfect ground cover where adense mat is needed. Or grow it between stepping stones.Its best in a moist soil in part shade.
Violas and violets—there are several kinds ofboth, all excellent for rock gardens. Violas,short-lived perennials, resemble small pansies,but are available in several solid colors, in-cluding purple, blue, apricot, yellow and white.Violets, with heart-shaped leaves, may be blue,purple, pink or white. They flower in spring andgrow luxuriantly in shade with plenty of moisture.The leaves remain attractive all summerlong.
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