Gardens in
which rocks and plants appropriate to them are the chief
landscape elements are called rock gardens or sometimes, if
the plants are entirely or mainly sorts to grow naturally at
higher altitudes or under subarctic or arctic conditions,
alpine gardens. Well planned and well executed rock gardens
are esthetically agreeable as well as horticulturally
stimulating.
Joy
of Rock Gardening
The
satisfactions of rock gardening lie not alone in creating
and maintaining pleasing landscapes, but also in developing
intimate acquaintance with and caring for the plants
accommodated. At its best, rock gardening is a splendid
hobby, not excessively demanding, yet sufficiently
challenging to reward reasonable dedication and attention.
Because the plants used are chiefly small, many sorts can be
accommodated in quite limited areas. This appeals to
gardeners with a well developed instinct for collecting, a
commendable expression of horticultural interest displayed
by many amateurs.
Another attraction of rock gardening is that, apart from
initial construction perhaps, the tasks connected with it
are generally light and agreeable. Most can be accomplished
while puttering around the garden at longer periods on more
fixed time schedules as some other types of gardening
demand.
English
Rock Gardens
Historically,
rock gardening began in the British Isles, its development
an outcome of the greatly increased numbers of travelers
from there who from early in the nineteenth century on
visited Switzerland and other mountainous parts in Europe.
Enamored by the great wealth of beautiful alpine plants they
saw, unknown in their own countries, they were inspired to
bring some back and attempt to grow them at home.
Because of a nearly complete lack of understanding of the
needs of alpine and other mountain plants most early
attempts at domesticating them were dismal failures. A few
of the toughest and more adaptable sorts survived in the
generally atrocious "rockeries" built by Victorians, but in
the main those horticultural conceits, which sometimes
included grottos, arches, bridges, and other elaborate
architectural features, became graveyards for the choicer
alpines enthusiasts had plucked from their mountain
homes.
But gradually improvement came. As early as 1870, William
Robinson, in his book Alpine Flowers for English Gardens,
attempted to give some guidance, and by the early years of
the twentieth century, an altogether better appreciation of
the needs of mountain plants had developed and skills in
cultivating them improved. Nevertheless, for a long time,
rock gardens continued to be poorly made and many
esthetically unsatisfactory ones were established, as,
sadly, are some modern ones. The least attractive belong in
the groups the inspired English authority Reginald Farrer
characterized as the almond pudding, dog's grave, and
devil's lapful styles and that later in America became known
as peanut brittle rock gardens.
Before the end of the first decade of the twentieth
century, capable Europeans were advocating sound principles
for constructing and planting rock gardens and for caring
for plants appropriate to them. Among the books in that
decade are My Rock Garden, by Reginald Farrer, whose famous
garden was in Yorkshire, England, and 'Rock Gardens' by
Lewis Meredith, who gardened in County Wicklow, Ireland.
Completed in 1913, but not published until six years later,
Farrer's book The English Rock Garden became the bible of
rock gardeners everywhere. A master of English prose, the
author stimulated thousands to attempt the cultivation of
the plants he so beautifully, entrancingly, and sometimes
extravagantly described.
Another benchmark was the publication, in English in
1930, of Rock Garden and Alpine Plants by Henri Correvon,
the distinguished Swiss pioneer in the cultivation of alpine
plants. As early as 1877, Correvon exhibited at a
horticultural flower show in Geneva a small collection of
alpines he had grown from seeds, for which pains he was
accounted a "young enthusiast who does not realize the needs
of the gardening world." Nevertheless, at the urging of one
of the judges who thought the Société d'
Horticulture de Genève should "give him something as
evidence that the Société is interested in
encouraging young beginners," Correvon was awarded a prize,
four little silver teaspoons.
American
Rock Gardens
In North
America, interest in rock gardens began later than in
Europe, yet in 1890 an example patterned after that at the
Royal Botanic Gardens, Kew, England, but much smaller, was
constructed at Smith College Botanic Garden, Northampton,
Massachusetts. In the 1920s, another was installed at the
Brooklyn Botanic Garden in New York City, and in 1932,
construction began on the Thompson Memorial Rock Garden (now
the T. H. Everett Rock Garden) at The New York Botanical
Garden in York City.
Meanwhile, keen amateurs were furthering the cause of
rock gardening on both coasts of America. The publication in
1923 of Louise Beebe Wilder's delightful book The Rock
Garden and the many other writings of this competent
cultivator and talented author stimulated many Americans to
engage in the new hobby.
Other circumstances that in the period between the two
world wars encouraged the rapid expansion of enthusiasm for
rock gardening were the organization of the American Rock
Garden Society and the truly marvelous examples of planted
rock gardens staged as exhibits at the great spring flower
shows in Boston, New York and Philadelphia, by the superb
artists of rock garden design and construction, Marcel Le
Piniac, Ralph Hancock, and Zenon Schrieber. The American
Rock Garden Society continues to flourish and to attract to
its membership people interested in its special field.
[Ed. note: ARGS membership in the United States and
Canada exceeded 4,000 at end of 1991 and includes many
members in other parts of the world. H. Lincoln Foster and
Laura Foster and their 1968 book Rock Gardening were vital
influences in America.]
Partly because of climate, which in many parts of North
America precludes or makes extremely difficult the
cultivation of many true alpines that are the glories of
European rock gardens, and partly because of the
availability of numerous charming small plants native to the
continent that are not alpines, most American rock gardeners
wisely do not limit their plantings to inhabitants of high
mountains, but include other neat and choice kinds that look
as if they properly belong. And this is as it should be.
Climate
and Plants
Traditionally,
and as generally interpreted, rock gardening involves the
cultivation of mountain plants and other low sorts that
withstand severe winter cold with impunity and is thought of
as belonging only in temperate climates.
But viewed as an art form based on the agreeable use of
rocks in the landscape, the development of rock gardens is
as appropriate in warm temperate, subtropical, and tropical
climates as in temperate ones. Certainly there are many
places in such regions where cliffs, outcropping rocks, and
similar formations are as inspiring as those of colder
regions, and the principles of adapting or constructing such
features as garden landscapes are not different.
The kinds of plants to employ in warm climates quite
obviously differ from those useful in colder ones, but
plenty are available. Fit choices to local conditions. In
desert and semidesert areas, cactuses and other succulents
in nearly endless array are obvious possibilities. They look
especially well in association with rocks. For humid warm
climate regions, there are available just as many sorts of
plants appropriate for displaying in rock environments. They
include ferns, as well as many kinds of begonias,
gesneriads, peperomias, and other plants, many of which as
wildlings inhabit cliffs and other rock features.
There are two chief types of rock gardens, natural and
artificial. The first represents the development of sites on
which native rocks are prominent as outcrops, cliffs, or
perhaps strewn boulders. The others are made in areas in
which all or most of the rocks used must be imported.
Existence of a site of the first description is reason
enough for adapting it as a rock garden, but constructed
gardens are generally only justified by a genuine desire to
grow and display small plants the majority of which are not
well suited for flower beds and borders. There are sometimes
rockless sites, such as banks and steep slopes, where the
development of a rock garden presents less problems than
other treatments.
Getting
Started
To begin a
natural rock garden, first make a careful survey of the site
and identify the plants growing there. Some, especially well
located, deep-rooted trees such as oaks and hickories that
can be relied upon to provide light shade for part or all of
each day in summer, besides adding to the charm and perhaps
majesty of the area, should be preserved, but remove
overcrowded, spindly specimens and weedy sorts of little
garden merit along with tangles of brushwood and similar
undesirable growth. There may be too, evergreen or deciduous
shrubs or herbaceous perennials, such as ferns, bulbs, and
other wildlings, that should be retained where they are or
transplanted elsewhere.
Clearing the area of unwanted vegetation may then be done
by digging out completely all roots as well as tops. Then
give attention to any pruning retained trees and shrubs
need. Cut out all dead and seriously diseased wood and, if
desirable, thin out branches from dense specimens. It is
often advantageous to provide for more side light by
removing some lower branches to "raise the heads" of trees
that cast too dense shade.
Rearrangement of a few rocks, or even supplementing those
on the site with others brought in, is permissible, but it
must be done so skillfully that even persons knowledgeable
about natural formations cannot easily detect the artifice.
Transported rocks must match precisely those of the site and
be positioned as though placed by nature.
Soil
Improving
the soil is the next order of business. Unless you are
dedicated to growing plants that need quite different types
of soil than what you have, do not attempt drastic changes
in its basic character. For example, if it is naturally acid
or alkaline accept the condition and select plants adapted
to it. Concentrate on bettering soil texture where needed by
mixing in such additives as chips of crushed rock, coarse
sand, perlite, or, for alkaline soil plants, crushed
limestone or crushed clam or oyster shells. For woodland or
moorland plants, add generous amounts of leaf mold, peat
moss, compost, or similar organic material.
Make certain there is adequate depth of soil, especially
in the crevices and crannies you intend to plant. It is
usually desirable to rake out existing soil and, if
necessary after deepening or enlarging the clefts or
crevices, to replace it with a better mix, firmly packed, so
no voids are left.
Planting is best done in early fall or early spring, but
not until disturbed ground has had time to settle or before
it is reasonably certain that it is essentially free of
pestiferous perennial weeds. Whenever practicable, it is
advantageous to allow an entire growing season to elapse
between the preparation of the site and actual planting.
This permits clearing the soil of weeds and ensuring clean
planting areas by pulling up or hoeing off every one as soon
as it shows aboveground.
Plants
and Placement
The
sorts of plants appropriate for natural rock gardens are
likely to include many native to the region as well as
others that thrive under similar conditions. In selected
spots and corners, avid rock gardeners are likely to try a
few more challenging sorts.
To be convincing, placement of the plants calls for an
appreciation of how vegetation is disposed on natural rocky
sites. Seek inspiration from such places, noting the
unstrained informality that prevails. Here, irregular drifts
of low plants may carpet the soil surface or occupy ledges,
shelves, or miniature plateaus, with very likely outlying
smaller groups or individuals, often at lower levels or to
the lee of the main groups, the outcome of seeds that have
fallen and been washed away or have drifted down from the
main colonies. Note how plants run along narrow crevices or
congregate at the bases of miniature cliffs. Without
slavishly copying such native features, let your natural
rock garden epitomize them and represent a distillation of
what is good about what you find in the wild, miniaturized
and tailored to accommodate the plants you want to grow.
Rocks
and Garden Construction
Rock
gardens constructed on sites devoid of native rock or where
little is present clearly offer opportunities for
imaginative development, yet in such places the most
inappropriate examples amusingly characterized by Reginald
Farrer, are often perpetrated.
Following Farrer's castigation, the better examples of
British rock gardens were made in what their builders fondly
imagined was a natural fashion, but because many of those
who made such gardens failed to study rock formations as
they occur in the wild, they were usually unconvincing.
At first, great emphasis was placed on creating "pockets"
to be planted with individual kinds of plants and the
structure was likely to consist of a series of such little
flat or nearly flat terraces backed by and supported by more
or less vertical walls of stone. Such was the rock garden at
the Royal Botanic Garden, Kew, England, until the 1930s, and
many others constructed in Great Britain and elsewhere
followed the same general plan. The pockets, frequently
referred to in garden writings of the time, were well
drained and bottomless so the soil with which they were
filled connected directly with the main body of earth
beneath and made it entirely practicable for plants to grow
and flourish, but the overall esthetic effect was rarely
satisfactory. But gradually improvements came, and between
the two world wars, gardens more suggestive of native rock
formations were developed both in Europe and America.
Choosing
the Site
The
choice of a site for a rock garden may be wide or limited
depending upon the extent and character of the property. The
advice so often given in older writings to locate the garden
well out of sight of buildings and other formal features,
is, on small grounds, often not tenable, and certainly is
not essential to success in cultivating alpines and other
rock garden plants.
It is by no means necessary to duplicate or even
approximate an alpine scene to achieve a satisfying and
beautiful rock garden. Such styles may be admirable in
suitable surroundings, but so are rock gardens of other
types.
It is even possible to install a garden adjacent to a
building or cropping out of a lawn without being
incongruous, possibilities earlier advocates of rock gardens
and some contemporaries completely reject. Furthermore,
garden features suitable for embellishment with rock plants
that make no pretense of naturalness, and yet are congruous
and beautiful, can be developed. To this category belong
what are known as dry walls, of which more will be discussed
later.
A secret of success of rock gardens that aspire to
naturalness, be they near or remote from manmade structures,
be they large or small, is the placement of the rocks. To be
convincing the effect must be that they were positioned by
nature without aid from man. Here, if ever, true art is to
conceal art.
The surest ways of obtaining such effects are (1) to use
the same type of rock throughout the garden or at least
throughout major parts of it, (2) to position each piece so
that it appears stable and, except for minor crevices,
connected with neighboring pieces aboveground such that the
whole apparently represents the exposed part of a massive
underground formation, and (3) if the rock be stratified, to
lay the pieces with the strata lines all in one direction.
Granted, because of geological or other disturbances the
disposition of rocks in the wild does not always conform to
these principles, the departure from them, unless carried
out very skillfully by one who has carefully studied natural
deviations from them, is very likely to produce uneasy
unconvincing effects.
Especially
appropriate sites for rock gardens are slopes, banks, and
small valleys or dells, natural or created, but flat areas
can also be utilized. A first necessity is to evaluate the
area, particularly with reference to any contouring that may
be desirable. If a pool, stream, or waterfall is
contemplated, and these can add greatly to the charms of
rock gardens. Their locations and courses must be planned,
and so, especially if the garden is sizable, must be paths
needed to enjoy and service the area.
Contouring is usually best achieved by stripping and
stockpiling the topsoil, fashioning the undersoil to the
convolutions and grades deemed appropriate (this may involve
bringing in additional material), then after modifying it in
any way that seems desirable, and if necessary supplying
additional soil to achieve a depth of at least 1 foot,
replacing the topsoil. Modification, if the soil is not
sufficiently porous, will involve mixing in generous amounts
of coarse sand, grit, or small chips of stone, and if
woodland plants are to be grown probably the admixture of
leaf mold, peat moss, or other suitable partially decayed
organic material. If a section of the garden is to be
devoted to plants that need alkaline soil, crushed limestone
or limestone chips may be included in the topsoil mix.
Finding
the Best Rocks
The kind of
rock used is usually determined by availability. Where
choice may be had, one that is porous, rather than such
hard, impervious types as granite and schist, is to be
preferred. Hard sandstone, and not excessively soluble
limestone are very satisfactory. But remember, limestone,
and water worn limestone is one of the most beautiful rocks,
are distasteful or unacceptable to such acid soil plants as
heaths, heathers, and rhododendrons. Tufa, a soft,
lightweight, porous limestone type rock formed by calcium
carbonate deposited in springs and streams, is easy to
handle and congenial to plants, but of undistinguished
appearance. Harder rocks can be used, but take longer to
weather because they are less encouraging to the growth of
mosses, lichens, and other primitive vegetation that soon
conceals freshly exposed portions of softer rocks.
Unless no other is available do not use newly quarried
rock. Its raw surfaces are likely to take a long time to
weather and, even worse, may display marks of drilling.
Weathered pieces collected from the surface of the ground
and of a character and color that suggest age are likely to
be ideal. In some parts of the country suitable material can
be obtained from old stone walls. The pieces must be of
manageable sizes and of acceptable relation to the size of
the garden, although here some "cheating" can be done for,
by careful placement, it is possible to arrange several
comparatively small rocks so skillfully that they appear to
be a creviced bigger one. When the chinks between them are
filled with plants that effect is greatly enhanced.
Boulders are generally considered unsatisfactory for rock
gardens, and certainly they should not be mixed with angular
rocks, but if boulders are all that is available it is not
impossible to fashion a convincing garden from them as was
done at the Brooklyn Botanic Garden.
The secret is to use boulders of different sizes and to
position them, some partly buried, some exposed, as they
would be in the bed of a dry stream or wash. Let the areas
between the stones slope gently except for some
accumulations of what represent washed down, stony, gravely,
sandy soil piled on the "upstream" side of boulders. These
accumulations may be level topped or even tilted slightly
against the prevailing slope.
Take care not to scar rocks when collecting and handling
them. To minimize the danger it may be worthwhile wrapping
choice pieces in burlap. Use crowbars, often necessary for
levering large pieces, although sometimes staves of wood or
pieces of two-by-four can be used for this purpose, with
care to avoid bruising the rock. If possible have rocks
delivered to the tops of slopes. It is easier to move them
downhill than up.
Spacing
the Rocks
When
constructing the garden, do not distribute the rock evenly
throughout; instead, make massive use of it in some parts,
employ it sparingly or not at all in others. Take a cue from
natural rocky places where accumulations of detritus and
washed or blown soil form slopes and terraces about and
between bold protrusions of rock. In gardens, rockless areas
afford relief to the eye, splendid opportunities for
planting attractively, and by contrast give seemingly
greater massiveness and importance to the rocky
portions.
Areas that lend themselves to rocklessness or to not more
than suspicions of rock poking through the surface are
gentle slopes downward and backward from the tops of cliffs,
moraine type slopes forward and downward from the fronts of
cliffs, valley like depressions between outcrops, and little
flats bordering streams and pools.
Installing
Special Features
Install the
most massive features of the garden first. These may include
bold outcrops, cliffs, and perhaps a waterfall. Give special
attention to the location of the last as well as to other
water features. Water spouting from the top of a hill or
cliff is all wrong; it lacks the appearance of naturalness.
To seem plausible, there must be, or by skillful
construction or planting the viewer must be led to believe
there is, a catchment area of considerable size above the
point of emergence to account for the volume of water.
Pools and watercourses call for special thought. The
supply may be natural, piped in, or recycled by a pump. If
artificial, be sure its source is concealed. With careful
planning, a comparatively small flow can be managed so that
it is seen more than once to give the impression that the
garden is much better supplied with water than it really
is.
Placing
the Rocks
When
placing the rocks begin at the low parts of slopes and work
upward, carefully setting each piece with its most
attractive weathered side exposed and, so far as consistent
with naturalness, with its top sloped slightly backward to
direct rain or water from sprinklers to the roots. With this
same thought in mind avoid overhangs that keep water from
reaching rock faces below them.
Strive to achieve a feeling of stability. Leave no
impression that the rocks are separate pieces susceptible to
being easily loosened and removed. This is most surely done,
so far as practicable, by setting each with its broadest
side as its base, a positioning that suggests the most
common aspect of exposed portions of outcropping rocks and
the usual attitude of surface rocks in the wild. To achieve
stability, with the rocks in their best possible positions,
it is sometimes desirable to prop a large rock on several
smaller ones and then to fill the voids with firmly packed
soil.
A variation of this procedure that, if skillfully done,
carries conviction and is highly satisfactory, is to stand
flat rocks, much thinner than long or wide, on edge with
their most attractive broad sides facing outward to form
miniature cliffs. In this way height is achieved with much
less bulk of stone than is required if one or two or more
superimposed pieces are set widest side down to produce
similar effects. When using such rocks take special care to
set them in positions of repose that allow of no easy
disturbance. This is particularly important in regions where
strong outward thrusting comes from the soil freezing
deeply.
No
matter how individual pieces are positioned, they must
relate to each other as though representing bedrock exposed
by natural weathering or as a result of gulleying by water
or wind. This means the major rock faces will have the same
general direction throughout the garden, and if the stone
shows lines of stratification they will be at the same angle
throughout. Minor exceptions are when rocks represent pieces
broken away from the main body and that angle downward from
the cliff like margins of a gullied stream or have tumbled
from a cliff to repose on a slope or plateau below.
Fairly small rocks may be effectively employed to give
the impression of being a bold outcrop.
Although it is true that natural outcrops occur in which,
as a result of geological upheavals, their lines of
stratification run vertically or nearly so, and there are
others in which they are approximately horizontal, it is
much easier and generally makes for the most satisfactory
accommodation of a considerable variety of plants if in
constructed rock gardens they are established at an angle of
from ten to forty degrees from the horizontal. This means of
course that the joints between the long sides of adjacent
stones will run similarly, which emphasizes the
stratification.
In
natural formations of stratified rock, fractures, called
primary joints, spaced from 1 foot or so to up to about 5
feet apart, commonly occur along the sides of up-tilted
masses, but not along their faces. These are at right angles
to the lines of stratification and cleave the rock into
approximately rectangular blocks. They may be simulated in
constructed rock gardens by positioning the ends of
individual stones to produce chinks and crevices that cross
the lines of stratification at right angles and where
exposed surfaces, which consist of superimposed pieces of
rock, extend through more than one layer. To accomplish
this, take care not to place the rocks like bricks in a wall
with their vertical separations staggered, but have them
above one another, with the chinks thus formed angling
downward from the tilted top of the exposed rock.
The ends of uplifted masses of stratified rock show no
regular system of primary joints, such as just described,
but they may be creviced vertically by frost action or as a
result of water running down them.
Whether the garden be big or whether it occupies no more
space than an average living room, the principles discussed
are applicable. Only scale differs. In large gardens, bolder
features necessitating the use of larger rocks are needed,
and by the same token, rockless or sparingly rocked portions
can be more expansive.
The final effect must be one of rightness, of belonging.
If the development adjoins a house or other building, make
sure it seems that the rock is native and the structure was
built upon it, rather than rocks have been brought in and
piled or positioned against or in front of the building. And
if your rock garden is to outcrop from a lawn or meadow,
perhaps rising no more than a couple of feet or so above
ground level, perhaps higher, let it, by the way it slopes
into the ground, suggest firm ties with imaginary underlying
bedrock.
Scree
and Moraine
A scree or
moraine is often included as part of a rock garden. Such
developments are patterned after natural features of the
same names that occur in mountain regions. Their special
characteristic depends upon the material of which they are
formed and into which the plants root. This mostly consists
of fragmented rock, in natural screes detritus collected in
rock slides and at the bases of cliffs, and in moraines
along the fronts and sides of glaciers. Natural moraines are
further commonly characterized by having flowing through
them some distance below the surface cold melt water from
the ice. It is less natural for screes to have any constant
flow beneath the surface.
Rock garden screes and moraines simulate to a degree
natural ones. Their purpose is to provide plants with
extremely well aerated rooting mixes of low fertility.
Surface water should drain through them rapidly, leaving a
film around each particle to meet the needs of the
plants.
To make a scree, which may well slope away from the base
of a cliff like rock or occupy a sloping gully, install over
a base of crushed stone or other very adequate drainage a
foot or more of a mix consisting very largely of crushed
stone or gravel, grit, and coarse sand with a small
admixture of topsoil. Approximate proportions may well be
one half by bulk crushed stone or gravel, and one quarter
part each grit or sand and soil, but these proportions may
be varied somewhat depending upon the character of
ingredients.
A moraine, in the horticultural sense, differs from a
scree, although the words are often used interchangeably, in
that a foot or two below its surface there is a constant
slow flow of water. This may be arranged by a shallow basin
of concrete or one formed of clay or of earth covered with
heavy polyethylene film as a base, with faucet or other
source of a trickle of water supplying one end and an outlet
at the other. To be most harmonious, arrange for the surface
of the scree or moraine to slope gently away from the base
of a cliff or down a gully and have a few pieces of rock a
little bigger than the average, of which the rooting mix
largely consists, showing at the surface.
Planting
the Garden
Planting a
newly built rock garden is best, but not necessarily,
delayed for a few weeks to allow for any settling of the
soil or rocks that may occur. But if each rock is set on a
firm base and the soil is packed well around it and between
neighbor rocks there will be little, if any, movement and
planting may begin as soon as convenient. Early spring and
early fall are the most propitious seasons for this
work.
When
placing the plants keep two objectives in mind, any special
needs of individual kinds and the overall effect you are
creating. If the first is not respected, as for instance the
need of dianthus for exposure to sun, of primulas for some
shade, of ramondas for a vertical crevice, of sorts finicky
about the pH of the soil for acid or alkaline areas, and of
other kinds for drier or moister soils, the growth, the
flowering, and even the permanence of the plants may be
adversely affected.
Endeavor to achieve a relaxed landscape, a feeling of
naturalness. If too many single plants of different kinds
are spotted around, or if there are not some areas,
fair-sized in relation to the extent of the garden, clothed
with low creepers such as thymes, creeping phloxes, or Mazus
to afford rest for the eye, the effect will be too busy. If
groups of the same kind are too equal in size, are of too
formal an outline, or are of individuals too evenly spaced,
the effect will be unnatural.
Some single specimens advantageously located may serve as
special points of interest. Especially appropriate for such
use are selected varieties of dwarf conifers, among them
arborvitaes, cedars, false cypresses, firs, hemlocks,
junipers, pines, and spruces. Occasional individuals of
other kinds of plants may be used similarly.
But for the most part, plant in informal groups and
drifts that suggest a natural ecological association of
kinds. This requires knowledge about how different sorts
will grow after planting. You may have this information. If
not, acquire as much as you can by observing other gardens
and by reading.
Groups may drift down gentle slopes, with the plants
closer together in the upper than the lower end of the group
and with perhaps a few specimens irregularly placed some
little distance from the low side of the main planting. Such
outliers suggest the results of seeds dropped or washed from
a higher place.
Other groups may occupy little plateaus, hang from the
tops of cliffs, or below crevices. They need not be clearly
defined. If adjacent groups mingle somewhat at their
margins, and if an occasional plant of one crops up as it
were as a seedling inside a group of another kind, the
effect of naturalness is enhanced.
No
matter how knowledgeable and careful you are, it is not
improbable that some errors of judgment will creep into your
selection of spots for some plants, but if these be
comparatively few they can be corrected later by
transplanting to sites that afford better growing conditions
or more appropriate display.
Choose time for planting when the soil is pleasantly
damp, neither wet nor dust dry. Make sure the roots of
plants dug in readiness for planting are protected from
exposure to sun and wind. Space individuals with some regard
for the amount of top growth they are expected to make. Do
not break the balls of soil in which roots are growing, but
spread roots not encased in soil in their natural positions
and work soil between them. Set the plants at the same
depths or very slightly deeper than they were previously,
firm the soil around them, and soak with a fine spray of
water.
Mulch
Depending
upon the kind of plant and the part of the rock garden it is
to occupy, the surface between individual plants may be
mulched lightly with chips or fragments of stone or, about
woodland plants in shaded areas, with screened leaf mold or
peat moss mixed with grit or coarse sand. For the best
effect, see that the stone chips consist of a mixture of
sizes and are of the same or closely matching kind of rock
to that of which the garden is constructed.
Care
of the Garden
Routine
care of the rock garden demands regular attention, but not
arduous toil. Beginning in the late winter or early spring,
the first task in regions of cold winters without an
adequate blanket of snow is the removal of the winter
covering. Do this before growth is well advanced and in two
or three stages rather than all at one time, so that new
shoots and foliage become gradually accustomed to full
exposure.
Choose dull, humid, quiet days rather than sunny, windy
ones for taking off the cover. Push back into place any
plants that have been heaved up by frost action and replace
any labels that have been disturbed.
Do not be in too great haste to cut back what appears to
be the lifeless tops of woody stemmed plants. Some may
surprise you by leafing later. But if you are certain they
are dead, do not hesitate, and at the same time clear away
dead foliage and any weeds overlooked from the previous
year.
Top dressing is next. Prepare a porous mix of topsoil,
peat moss and grit or coarse sand as a base and modify it as
needed for particular areas of the garden devoted to plants
with special needs by adding additional peat moss for acid
soil plants, crushed limestone or agricultural lime for
lovers of alkaline soils, bonemeal for plants likely to
benefit from some extra nutrients, and for kinds known to
appreciate richer diets, such as primulas, some old rotted
or dried commercial cow manure. But beware of using too much
fertilizer. The vast majority of rock garden plants thrive
in rather lean soils and become too lush and gross in those
too fertile. Before spreading the top-dressing, stir the
soil shallowly with a hand cultivator so that the new layer
will integrate with the old.
Summer care consists chiefly of weeding, watering (do
this only when clearly needed and then soak the ground to a
depth of several inches), and taking off faded flowers, plus
a certain amount of propagation. Weeding calls for special
knowledge. In a garden containing many species and varieties
it is not a job for a novice or an odd-job man. Not
infrequently, choice plants that perhaps have defied the
gardener's best efforts to propagate reproduce voluntarily
and one or more precious seedlings will appear in some
unlikely spot, in a crevice, on a little plateau, or perhaps
among some spreading plant of another kind. Only the keen
eye of an experienced rock gardener is likely to detect such
dividends, with the result that instead of being ruthlessly
rooted out they are nurtured to add yet further glory to the
garden. Besides, weeding in a rock garden can be a
delightful task, one that gives opportunity to know one's
plants more intimately, to observe their manners of growth,
and to note their individual idiosyncrasies, that is, if
weeding is done when it should be, at the very earliest
evidence of the weed growth and before it has begun to take
over from the rightful occupants.
In the fall a general cleanup is needed. Cut back the
dead tops of plants that are not evergreen and make
comfortable for the winter all that are perennial. This is
the time, too, to plant hardy spring flowering bulbs.
Winter protection in regions where hard freezing is
experienced, but a continuous snow cover cannot be relied
upon, is necessary, but it is easy to overdo this. Do not
install the cover until the ground is frozen to a depth of 2
or 3 inches, otherwise mice and other rodents may establish
winter quarters and harm plants. A covering of branches of
evergreens (discarded Christmas trees are fine for this
purpose) such as pines, spruces, or hemlocks, is ideal. Or
salt hay can be used. It is important that air circulates
freely through the covering. Common errors are to put in
place too early and too thickly.
Propagating
the Plants
Propagation
is an important phase of rock gardening. Many of the very
finest rock plants are comparatively short-lived or are
fickle in cultivation. This makes it necessary always to
have at hand a stock of young plants to replace those that
may succumb to the heat and humidity of the summer, to the
extreme conditions of winter, or to other causes. Raising
young plants is fascinating work and makes a particular
appeal to the real plant lover.
Rock garden plants are increased in several ways, and the
method followed in any particular case will depend upon the
character of the plant, the availability of propagating
material, and the percentage of increase desired.
Plants of a mat forming type, such as creeping thymes,
Mazus, and Draba repens, are easily increased by simple
division of old sods. This method also serves splendidly for
many kinds that form clumps, as do most veronicas, primulas,
and asters. If more rapid increase is desired, or if
divisions are not obtainable, cuttings afford an alternative
method of securing additional stock. Seed provides an
excellent means of obtaining stock of many wild species of
plants, but it is not reliable for garden varieties or for
improved kinds that you may want to grow. Then again, the
species of certain genera hybridize very freely if they are
grown near to one another, thus seed collected from any such
species growing in a garden where others of the same genus
are grown will very likely result in hybrid progeny of
unpredictable characteristics and desirability. Dianthus,
aquilegias, saxifrages, and sempervivums are typical of this
group.
Many rock garden plants can be propagated in the spring.
September is also an excellent time to attend to this work,
for at this season the trying conditions that have prevailed
during July and August no longer have to be faced, and the
young plants still have an opportunity to become established
before the onset of winter. Stock of kinds known or
suspected not to be reliably hardy must be established in
pots and plunged to the rims of the pots in a bed of sand in
a cold frame for the duration of the winter.
Division is, of course, the simplest means of
propagation. All that is necessary is to lift the parent
plant and carefully divide it into suitably sized portions,
each with some roots attached. If the plant has a great deal
of top growth, this is usually cut back somewhat to
compensate for the unavoidable root disturbance caused by
the operation. The divisions are then planted directly back
into the rock garden or potted into the smallest size pot
into which their roots can be comfortably fitted in a soil
mixture similar to, but lighter than that in which
established plants of the same kind are known to thrive. The
addition to the soil mixture of a liberal amount of grit or
coarse sand ensures lightness. Shade from strong sunlight
must be provided, at least until new roots have thoroughly
taken possession of the medium in which divisions are
growing.
A cutting is essentially a division without roots that,
if placed in an appropriate environment, may be expected to
develop a new root system. Until new roots are sent out,
cuttings require special care, and every effort must be made
to provide conditions favorable to root development. The
medium in which cuttings are planted is usually clean,
coarse sand or perlite kept constantly and evenly moist, but
some kinds, for instance heaths and heathers, root more
readily in a mixture of sand or perlite and peat moss.
Protection from currents of moving air, shade from direct
sunshine, and the maintenance of humid atmosphere check
excessive transpiration and evaporation. This is important
because if the cutting continues to lose from its tissues
more moisture than it is able to replace, it quickly withers
and dies. A well managed cold frame provides suitable
conditions for rooting cuttings of a great many rock garden
plants. If a considerable number are to be inserted, install
a 3 to 4 inch deep bed of the rooting medium in the frame.
For lesser quantities, a flat will suffice. Be sure that the
medium is moist and packed down firmly by pounding it with a
brick or an equivalent tool.
The cuttings will vary in length according to kind, the
smallest perhaps not exceeding � inch, the largest up to 3
inches. Cut them cleanly across with a keen knife or razor
blade at the base just below a joint or node, and trim off
the lower leaves. Plant them so the base of each sits
squarely on the bottom of the hole it occupies, and pack the
sand firmly against it. After the cuttings are planted,
water them thoroughly with a fine spray, and then cover the
frame with the sash. In the beginning, ventilate not at all
or at most sparingly and provide shade from direct sunshine.
But when the cuttings commence to form roots, more
ventilation and less shade are in order and finally the
young plants should be exposed to the ordinary outdoor
conditions that suit their kind.
As soon as good root systems have developed, transplant
the new plants into small pots. Use a gritty or sandy soil
mix and make sure of good drainage by putting into the
bottom of each pot a few crocks. After potting, sink the
plants to the rim of their pots in sand or peat moss in a
cold frame.
Plants
from Seed
Raising
alpine or other rock garden plants from seed sometimes
brings interesting problems, but it is impossible to
generalize as to procedures except in the broadest way.
Experience and observation suggest that the importance of
compounding exact soil mixes to meet the requirements of
individual species is frequently over stressed. In their
early stages at least, the vast majority of plants can be
successfully raised in one of three distinct types of soil.
The first contains lime, preferably in the form of ground
limestone, but ordinary builders lime will do. The second is
free of lime, but contains an abundance of leaf mold or peat
moss. The latter is particularly desirable for plants known
to need an acid soil. The third is an ordinary, porous seed
soil, such as you would use for the majority of garden
annuals, but considerably more gritty. This type will be
used most often, since the majority of plants thrive in it
during their early stages. Lime loving plants such as
encrusted saxifrages, need the first mixture. Woodland
plants in general prefer the second mix. Of far more
importance for most sorts than the exact chemical reaction
of the soil is its physical condition. It must be porous and
drain freely.
Pots, pans, or flats, according to the amount of seed to
be sown, may be used. Most gardeners agree that it is
desirable, after sowing, to expose the seeds of alpine, to
or near freezing temperatures for a few weeks before putting
them into a cool greenhouse or similar environment to
germinate. But often the most practical plan is to sow seeds
as soon as they are obtainable. Many will germinate in a few
days to a few weeks, others may take several months, even a
year or longer. Keep those that do not germinate quickly
moist, and in fall sink their containers to their rims in a
bed of sand or peat moss in a cold frame or outdoors. They
may be left there until they germinate, or to hasten
germination, they may be brought into a cool greenhouse in
February. Alternatively, mix the seeds with slightly damp
sand or peat moss and store them in a plastic bag in a
refrigerator at 35 to 40°F for three or four months
before sowing.
Detailed care following germination plays an important
part in the degree of success attained. It is particularly
important that the soil be kept uniformly moist. When the
seedlings are of such size that they can be transplanted, a
little more thought than when seed sowing should be given to
the exact soil mix most suitable for each particular kind.
Only by experience and experiment, and often a certain
amount of error, can these facts be determined, for above
all, it is unwise to be too dogmatic about a subject having
such wide ramifications as this. Frequently, gardeners
following widely different practices get equally good
results provided fundamental principles are not
violated.
Rock garden plants for temperate and cold temperate
climates include a vast array of alpines as well as natives
of lower elevations that, by custom and for convenience, are
accepted as appropriate. Most are species and varieties that
somewhere occur as wildlings, but practically all rock
gardeners admit a selection of garden varieties and manmade
hybrids. These are usually limited to sorts that look as if
they could be natural species and varieties, although this
is scarcely true of a few that have double flowers.
Nevertheless, it is generally considered inappropriate to
admit plants of distinctly gardenesque appearance, those
that strongly suggest the hand of the plant breeder.
Meetings
The
sorts of plants appropriate for natural rock gardens are
likely to include many native to the region as well as
others that thrive under similar conditions. In selected
spots and corners, avid rock gardeners are likely to try a
few more challenging sorts.
The
choice of a site for a rock garden may be wide or limited
depending upon the extent and character of the property. The
advice so often given in older writings to locate the garden
well out of sight of buildings and other formal features,
is, on small grounds, often not tenable, and certainly is
not essential to success in cultivating alpines and other
rock garden plants.
Especially
appropriate sites for rock gardens are slopes, banks, and
small valleys or dells, natural or created, but flat areas
can also be utilized. A first necessity is to evaluate the
area, particularly with reference to any contouring that may
be desirable. If a pool, stream, or waterfall is
contemplated, and these can add greatly to the charms of
rock gardens. Their locations and courses must be planned,
and so, especially if the garden is sizable, must be paths
needed to enjoy and service the area.
No
matter how individual pieces are positioned, they must
relate to each other as though representing bedrock exposed
by natural weathering or as a result of gulleying by water
or wind. This means the major rock faces will have the same
general direction throughout the garden, and if the stone
shows lines of stratification they will be at the same angle
throughout. Minor exceptions are when rocks represent pieces
broken away from the main body and that angle downward from
the cliff like margins of a gullied stream or have tumbled
from a cliff to repose on a slope or plateau below.
In
natural formations of stratified rock, fractures, called
primary joints, spaced from 1 foot or so to up to about 5
feet apart, commonly occur along the sides of up-tilted
masses, but not along their faces. These are at right angles
to the lines of stratification and cleave the rock into
approximately rectangular blocks. They may be simulated in
constructed rock gardens by positioning the ends of
individual stones to produce chinks and crevices that cross
the lines of stratification at right angles and where
exposed surfaces, which consist of superimposed pieces of
rock, extend through more than one layer. To accomplish
this, take care not to place the rocks like bricks in a wall
with their vertical separations staggered, but have them
above one another, with the chinks thus formed angling
downward from the tilted top of the exposed rock.
When
placing the plants keep two objectives in mind, any special
needs of individual kinds and the overall effect you are
creating. If the first is not respected, as for instance the
need of dianthus for exposure to sun, of primulas for some
shade, of ramondas for a vertical crevice, of sorts finicky
about the pH of the soil for acid or alkaline areas, and of
other kinds for drier or moister soils, the growth, the
flowering, and even the permanence of the plants may be
adversely affected.
No
matter how knowledgeable and careful you are, it is not
improbable that some errors of judgment will creep into your
selection of spots for some plants, but if these be
comparatively few they can be corrected later by
transplanting to sites that afford better growing conditions
or more appropriate display.