Here there are fewer existing, desirable locations for rock and wall
gardens. But for the sake of enjoying the dainty plants, and of marking
your garden with originality, you may want to create a site. It is
possible to dig out a “natural” depression or build up a slope, if it’s
skillfully designed--and if you can get rocks that don’t look foreign
and far away from home. Or dig down a foot or two to make a formal or
semiformal sunken garden, the beds raised and held in place by a dry
wall with crevices to plant in, and flagstone walks.
Corners sometimes offer possibilities--a far corner, where there is a
background of trees, fence, or wall; or a front corner where the lawn
slopes slightly down to the sidewalk. Or there may be a place near the
patio for a tiny pool in a rocky setting.
A birdbath, sundial, or shrine that’s a focal point in a small garden
can sometimes be embellished with a small rock garden at the base.
So can the edge or corner of a raised patio. Terrace pavements with
cushions of thyme rooted in the crevices are enriched with color,
fragrance, and texture. The lines of stark steps are softened and the
appearance mellowed by crowded clumps of fat sempervivums. Wherever
you can find reason for a rock wall, or even a row of rocks laid
horizontally and only a few inches high, you can plant it with rockery
plants at top, bottom, or in between. In the artificial settings of
many suburban lots, semiformal walls separating two levels of lawn
or supporting the edge of the family living area are very suitable
substitutes for rock gardens.
MINIATURE ROCK AND WALL PLANTS
One of the main virtues of rock and wall gardens is their
individuality--they don’t look like other gardens, or even like each
other. But commonplace plants such as bedding petunias can cancel
this distinctiveness in a minute. If you use annuals at all, get less
ordinary varieties and use them sparingly, for temporary color in a
bare spot or over the dying foliage of spring-flowering bulbs.
The plants that look best with rocks are those that grow naturally
among them. Hundreds of rock-loving plants are available, and more
hundreds of alpines from rugged mountain heights. Only the easier
alpines are included here, the most adaptable to more luxuriant
climates and soil, the least likely to pine for their rigorous,
high-altitude homes. Tricky types from above the timber line are left
to the dedicated collector.
[Illustration:
Saxifraga seedlings--a natural rock-loving plant]
Nurseries and catalogues of rock-garden specialists are so full of
distinctive and delightful miniature plants that my first reaction
was blissful delirium. And after I acquired as many enticing items as
I could, my second thought was: These gems are too little known and
grown. So I began to sort out some that might flourish in our small
perennial borders. With favorable conditions of drainage and air
circulation, a number of rockery plants have already made themselves at
home in other, rockless gardens.
Most miniature bulbs are effective in rock gardens, and some miniature
perennials--not ubiquitous types, and not those that spread voraciously
by runners. Miniature shrubs and trees are indispensable in rock
gardens of all sizes--to give variety, contrast, and substance; to
act as accents; to create boundaries or backgrounds. Use them with
restraint. Place spreading, wind-swept types at the top, bushy shapes
down lower, upright exclamation points at the very bottom. Make sure
they are in scale with the rocks, the plants, and the garden as a whole.
Select all kinds of rock and wall plants for their effectiveness of
form, texture, and color in the complete design. And this repetition
is important and unavoidable. Select varieties that naturally like, or
will adapt to, the cultural conditions like sun and soil type you have
or can provide.
MINIATURE ROCK GARDENS
For setting a few rocks into the side of a handkerchief-sized section
of slope, or building many more into a garden in a good-sized corner,
there are a few guiding principles that will help make sure you are
happy with the result. Most important, have your design as complete
as possible before you start to build. A sketch drawn to scale is
a valuable visualizing aid. Then, make your construction solid and
substantial, and favorable to plant growth and health.
If you have a choice of exposure, face a sloping rock garden toward the
north or northeast, so it will get enough summer sun but not so much
that it dries and cooks. Shrubs and trees in the background should not
create dense shade in the garden, nor drip moisture on the plants and
steal nourishment from their roots. Drainage is extremely important
in selecting a site. If the subsoil is packed and clay-like, you can
either replace it, make it more porous, or select another spot.
What kind of rocks to use and where to get them depends on the part
of the country you live in. Anything that’s indigenous to an area
is first choice, always. Limestone, sandstone, fieldstone, porous
tufa--native rocks “belong” as no artificial or imported rock ever can.
If your land is not blessed (or cursed) by plenty of rocks, you can
sometimes collect them near rivers, mountains, or abandoned quarries,
or where a new road is being blasted through. Whether you have them,
collect them, or buy them, all the rocks in one garden (or on the same
property) should be of the same general type. Varicolored geological
specimens are seldom attractive.
Consider each rock’s characteristic color, texture, size, and shape
before you decide where to place it, or whether to place it at all.
Even in the tiniest rock gardens, tiny rocks look ridiculously
salt-and-peppery. Start with rocks of substantial size, in keeping with
the size and contour of the garden; use smaller ones where they fill in
effectively.
Naturally worn and weathered rocks look more natural than freshly
chiseled surfaces; irregular, angular forms are better than uniformity.
Rocks with stratified layers suggest ledges and cliffs. Glacial
boulders or “hardheads” are not good in formal patterns. Use them
naturalistically, in varying sizes, arranging them with studied
carelessness as if they’d been scattered haphazardly and then left.
Avoid overcrowding with so many rocks that the plants are overshadowed
by the debris. Place rocks as they might lie naturally, partly buried
in the soil, the tops smoothed over by the elements, and so solid that
they don’t wobble when you step on them.
_Construction_
Perfect drainage, so that water cannot stand around the roots and
crowns, has been called “the most important need for all alpine
plants.” The selected location (raised or sunken) and composition of
subsoil and topsoil can either contribute to good drainage or deter
it. In small gardens it’s not too formidable a job to install a system
of drainage tiles, if necessary, or to add gravelly sand to subsoil to
make it more porous. Easy insurance in any rock garden is to start with
several inches of rather coarse gravel or rubble as a bottom drainage
layer.
Any topsoil that is removed during construction should be saved
carefully. If you can pile it in the center of a tarpaulin or piece of
strong burlap, it can’t be scattered and lost; and you can also mix it
with any additives with pleasurable ease. Simply pile on the peat, leaf
mold, sand, or other ingredients; then, holding opposite corners (you
may need a helper to hold one corner of a large piece), pull it back
over the soil pile and fold it over the other end. Repeat this, from
opposite ends, until the materials are thoroughly mixed.
The first rocks are usually set at the lowest part of the garden,
partly sunk in soil or otherwise made extra-sturdy and secure. Build up
from that point, arranging rocks with their broadest surfaces at the
bottom, all lines of stratification horizontal or on the same slant.
Each rock should slant slightly inward and downward, to catch moisture
and encourage it to run into the soil in the garden.
Provide plenty of soil for spreading roots, and a minimum depth of
eighteen inches or more. Plants in shallow pockets may be stunted and
will certainly dry out too fast during droughts. Whether or not you
plant as you go depends partly on your agility. Don’t crush the first
plants under your feet or knees as you set rocks and plants above them.
It’s often faster and easier to spread out roots and make soil firm
around them before the next rock is set in place.
_Planting_
Set plants as deep as they were planted before; no deeper (danger of
crown rot) and not too shallow (they may dry out). Tuck them firmly in
cool, moist, rock-shaded soil. Keep the soil constantly moist until
firm new growth shows that the roots are established and growing.
Rock-garden plants are seldom suitable for planting in neat rows or
geometric patterns. Tiny, slow-growing types are arranged in groups of
three or more; one or two spreaders per planting spot will do. Don’t
crowd these plants. Give them room to develop and for air to circulate
around them, and to display their charms at their best. Provide private
quarters for the smallest gems, away from hearty growers that might
overpower them. Keep color combinations and contrasting textures in
mind. Set trailers where they can droop over stones. Place those that
like moisture low in the garden; their roots keep cool in the shade of
rocks.
As a finishing touch, after the rock garden is built, planted, and
thoroughly watered, cover all soil surfaces with a mulch of fine gravel
or stone chips. Work it up to each crown, under prostrate stems.
Aesthetically, this gives a neat, well-groomed look and ties plants,
rocks, and setting into one coherent picture. Functionally, the chips
absorb heat and keep soil cool and moist, lift small, low leaves out of
mud and water, discourage slugs, protect crowns against rot, and firmly
discourage the intrusion of weeds.
MINIATURE WALL GARDENS
Any small section of low wall--brick, cement, stone, or concrete--can
be the background for a miniature garden. But it is in a dry wall,
built of stones without cement, that many small rockery plants best
display their jewel-like perfection. Planted horizontally, with their
roots in pockets between the rocks, they make a vertical rock garden of
glowing colors and fascinating foliage textures.
For small, low walls, and those in somewhat formal settings,
thin-layered rock such as slate or shale is usually preferred.
Irregularly shaped fieldstone or other rocks of native origin are used
in more natural, informal designs. Any lines of stratification are, of
course, laid horizontal and parallel to each other. Another good rule
to go by is: The smaller the wall, the smaller the rocks.
_Construction_
Low walls (two feet high or less) usually do not need a foundation
layer sunk below the frost line. They can be started at, or just under,
ground level. But they must be set solidly on a firm, wide base--two
feet wide, for example, for a wall two and a half feet high. Set the
largest stones and complete the lower layer first. Tilt each rock
slightly backward and downward so soil won’t wash out of pockets, water
will run back to plant roots, and the heaving pressure of frost won’t
thrust the rocks out of place in winter. A guide line of string or wire
moved up with each new layer will help you keep the construction level.
The wall should slant slightly in toward the bank behind it, and
usually grows more narrow as it goes up. Each layer is made absolutely
solid before the next is applied. Set each stone so that it is
completely steady, and rests on parts of two stones beneath it. This
distributes weight evenly, avoids crushing plant roots, and prevents
unattractive and impractical long, vertical cracks created when joints
coincide. Use small, flattish rocks to fill chinks under large stones
and make them steady.
Behind the wall, as you build, firm in a goodly layer (one foot thick
is usually recommended) of topsoil that has been enriched and aerated
to promote drainage. Roots will reach back here for water and food. As
you ram soil into pockets, make sure it reaches all the way back to
this layer. Unless all the soil is made very firm, it may settle and
the stones may slide out or into the bank.
At the top you can leave some pockets for plants, or plant them just
behind the wall. Cover cracks at the top with flat stones, so water
won’t wash out soil.
[Illustration: A rock, a rose, and a miniature rose.]
_Planting_
If you can remember not to damage plants at the bottom as you’re
working above them, set the plants in each layer as you build. It’s
easier then to make sure the roots are firmly embedded well back into
the soil. Plant sparsely; leave plenty of room for growth and
spread, and plenty of uncovered wall surface to contribute pattern and
texture to the picture. Space the plants at irregular intervals, never
in straight lines either horizontal or vertical. Water thoroughly,
making sure the layer of soil behind the wall is completely moist; and
keep it moist at least throughout the first growing season.
PATHS AND PAVING
Many little rock plants will make soft cushions and carpets, with
their roots in crevices between pieces of paving, and also in stone
steps. They’re very low-growing and very hardy, and usually spring back
resiliently when stepped on. It’s important that acid-loving varieties
not be planted near cement, which sometimes neutralizes or alkalinizes
the soil. And, of course, the situation should provide the amount of
sunshine and moisture the plants need.
The simplest kind of informal path or paving for an informal patio
consists of flagstones or slates set in the ground, the top level flush
with the surface of the soil. Plants are spaced irregularly in cracks
between the stones. I’ve seen one path of old millstones laid this way,
the plants rooted in the center hole.
Bricks create a more formal pattern, either laid on a bed of sand
or set into a foundation of concrete over gravel. The popular
“crazy pavings” can be odd pieces of either brick or stone arranged
in any conceivable pattern and laid in mortar. In any such solid
constructions, planting pockets should be scooped out before the
concrete sets hard; or a chunk of wood can be inserted to hold the
space open.
Give the carpeting plants as much good soil as you can, and keep them
moist until they are growing well. Occasional trimming will stop them
from growing straggly, and keep them neat, compact, and in a pretty
pattern.
PLANTING AND CARE
Planting times vary according to climate and season of dormancy. In
warm areas it’s almost always late fall. Where winters are rugged, it
can be during brief semidormancy in early September, but it’s safest
in early spring when severe frosts are no longer likely and favorable
weather blesses plants at the height of their annual growing power.
In temperate sections spring-flowering varieties can be planted from
mid-August through October, others in spring.
[Illustration:
Lemon thyme and ivy showing results of being trimmed and kept
neat
_Mr. and Mrs. Alex O’Hare_]
Strong, healthy, pot-grown plants can be planted throughout the season
in almost all areas. They transplant easily, with little disturbance
and shock. In fact, whenever we acquire plants during the fall, we
keep them in their pots or pot them up, and protect them in the cold
frame during the winter. One of my favorite and most knowledgeable rock
gardeners tells me that he always pots tender or difficult plants, and
keeps them potted until their roots are fully developed, before he sets
them out in the garden, no matter what the season.
_Soil_
Providing the proper soil is vitally important to rock-garden plants,
and particularly to alpines. They’re naturally dwarfed by the rough
conditions in their native mountain areas. But when they move down
to our comparatively lush climates and longer growing seasons, they
respond to a too-rich diet by growing too tall and rangy, with too few
flowers, and they lose their charm. They do need some nourishment, of
course. And they are extremely sensitive to soil textures and drainage
conditions. Heavy, soggy soil causes them to rot quickly. Soil that
lacks organic matter dries out too fast.
Because of climatic and other variations, I hesitate to set down any
“ideal soil mix” for these plants. Instead, I suggest a basic formula
that can and should be varied according to the aridity or rainfall
in your area, the size and location of your rock or wall garden, the
composition of your garden soil, the availability of some ingredients,
and the personal preferences of the plant varieties you want to grow.
Here it is:
Three parts fairly friable, fertile loam.
Two parts humus--peat, leaf mold, compost--for lightness and fertility.
Two parts stone chips or crushed rock--perhaps the most important
ingredient, to keep soil open and cool.
One part sharp builders’ sand, or the gravelly sand used in mixing
concrete, to lighten heavy soil and promote drainage.
If your garden loam is sandy or gravelly, of course, you would increase
the proportion of humus. If it’s rich in organic matter, you would
decrease the quantity of humus. Very sticky, heavy clay soils are best
replaced.
Rock and alpine plants are also particularly sensitive to the acidity
or alkalinity of soil. This is measured by the _p_H scale, ranging
from very acid _p_H 4.0, through 7.0 at neutral, to very alkaline
9.0. Rock-garden specialists usually indicate the preferred _p_H
for the plants they sell.
By using a soil-test kit or, better still, sending a sample to your
state agricultural service to be tested, you can easily find out
whether the soil in your garden is acid or alkaline, and to what
degree. Then, to make acid soil more alkaline for plants that need it,
mix in small quantities of agricultural lime--the amount depends on
the degree of acidity and on the plant itself. Don’t overdo it. Too
much lime can do as much harm as good. Alkaline soils are not quite
so readily converted to acid, but you can use oak-leaf compost (not
completely rotted), acid peat, or pine “duff” (rotted pine needles). Or
you can be satisfied with the tremendous number of rockery plants that
really prefer alkaline soil. These preferences vary, not only between
different plant families, but also between individual members of the
same family.
For our small gardens, I’ve found it not too tiresome to provide soils
of several types. For specially precious plants, I often mix special,
small batches of soil. Then I clean out the planting pocket, make sure
that it is tightly closed in with rocks so water won’t wash this soil
out or other soil in, and refill it with the preferred mixture.
_Watering_
Except during rare droughts in spring, when the plants are in active
growth, we seldom have to water our rock and wall garden. Our summer
rains are usually sufficient for their needs. But whenever or wherever
there are long weeks of extreme heat and dry winds in summer, water may
be needed. Use a fine spray gently, so that the small plants won’t be
washed loose. And let the water soak in long enough so the entire area
is moist in depth.
_Fertilizing_
Some rock plants can take and use fertilizer, in spring; but most
alpines are better off without it. For them, we mix a little leaf mold
with the gravel mulch when we renew it. For the more ordinary types, we
provide a very light feeding of whatever balanced fertilizer we have on
hand.
_Grooming_
In rock gardens (and particularly in very small rock gardens) even
slight untidiness or imperfection shows up all too clearly. But I
consider it a pleasure to weed and care for the little plants a few
minutes every weekend. Faded flowers are snipped off. Weeds are removed
with determination, but with gentle protection for any small, weak
plants. Spreading shoots that grow long and out of line are cut off, or
sometimes uprooted, and removed. Louise Beebe Wilder says it’s an art
to keep a rock garden in balance, with the proper proportion of plants
against stones. And she is an artist with hers.
In spring, even before the last of the winter mulch is removed, we look
for cracks in the soil and for plants that have been heaved out by
frost, and press them firmly back into place so their roots can take
hold again. We also fill any washed-out pockets with fresh soil mix,
and top-dress any low areas. Any rotted leaves and stems and other
debris are removed; and the entire garden gets a thin fresh layer of
stone-chip mulch.
In fall there’s the general cleanup operation--weeding, pressing in
loose roots and packing them with soil, trimming back rambunctious
growers, replenishing the mulch of stone chips if needed.
_Winter Protection_
If you can count on a continuous cover of snow over your rock garden
all winter, there’s little you need to do for these hardy little
plants. But we can’t; we have the danger of alternate freezing and
thawing that can do so much damage. So we provide special protection.
In winter, after the ground is frozen at least an inch deep, we cover
the complete garden with salt-marsh hay. (Some types of Fiberglas,
and wood excelsior from packing cases, are also suitable, reusable
materials). This light, airy blanket keeps plants cold and dark, yet
gives them air to breathe. If it threatens to blow away, we hold it in
place with a few light evergreen branches.
PROPAGATING ROCK-GARDEN PLANTS
These are, of course, perennials and with slight variations can be
propagated like other perennials. (See pages 255–59.)
_Seeds_
Some need a pre-germination cold and some don’t; some germinate best
at cool temperatures, some at warm; some need light, others need dark.
Check seed packet, catalogue, or reliable reference book for specific
information for each type of seed.
We start seeds of delicate varieties in the greenhouse, where we can
hover over them, in late winter; others may be sown in the cold frame
in March or April, so the plants will be as mature as possible before
their first winter.
_Stem Cuttings_
For the smaller plants, these can be as short as three inches or less.
Try to take snappy new growth, neither weak and watery nor hard and
tough. Sharp sand is a suitable rooting medium for many types.
_CHAPTER 12_
MINIATURE POOLS AND
WATER PLANTS
If you can work out a way to use water in your landscape, by all means
do. Whether it’s a dime-sized tub the birds dip into, or a full-scale
formal pool in a tiled patio, any garden with water attracts immediate
attention, gives quick pleasure, becomes an unquestionable center of
interest. Actually, the excitement water adds to any landscape scene
is the antithesis of its calm, cooling, serene effect. I don’t know of
any other feature that, with a few plants and a minimum of care, makes
a garden spot at once so dramatic, artistic, and restful. And if the
water moves--ripples through a stream, drips over stones, falls from
one level to another--soothing sound is added to the other assets.
Natural brooks, streams, and pools usually require little designing
beyond bringing out the best of their inherent beauty. But there’s also
not a suburban lot for which some kind of artificial water garden can’t
be designed, and few grounds that are not thereby enhanced. The only
requisite is that the design be in harmony and scale with its setting;
that it be conceived, located, and constructed with imagination and
skill.
The fact that pools are inevitably natural focal points makes their
faults more obvious and more difficult to correct. The most you can do,
once a pool is in the ground, is to soften or otherwise improve its
outline with coping, rocks, or plants. If there’s too much cement, you
can’t hide it with aquatic plants without covering, too, the desirable
reflections on the water. If it’s too small, you can hardly make it
larger. If the shape is uninteresting, you can’t change it very easily.
If it’s in the wrong spot or faced the wrong way, you can’t move it.