TREES AND SHRUBS FOR THE ROCK GARDEN
If we think of the changes in gardening terms which have occurred during
the last quarter of a century, there is surely significance in the
gradual transition from the Rock Garden or Alpine Garden into the more
imposing Rock Garden of our present-day language. It points to the
bolder grouping--now happily adopted in most good gardens and more in
accordance with Nature's pattern--which includes evergreen and flowering
shrubs as well as the close-growing alpine plants, gem-like in their
brilliant colours, which in earlier days were alone considered suitable
for the purpose. The principle is now generally recognised that the
"unstudied picturesqueness of Nature may be brought into the rule and
line ordering of our gardens," and the better construction and
government of the Rock Garden gives greater scope for the carrying out
of this worthy effort.
In enumerating suitable shrubs for the Rock Garden, more than ordinary
care should be exercised in their selection, in view of the greater
difficulty of rectifying mistakes in such positions. We must not be led
away by the beauty of a shrub, for instance, during its time of
flowering alone, without considering its character at other seasons and
its adaptability to its special surroundings. A due sense of proportion
will also hold us back from planting a spreading, hungry-natured shrub
in limited space, or where it would rob and over-run more valuable but
weaker plants. Such considerations as these must be left to the planter
who, in his turn, must be guided by the incidental circumstances of his
particular locality. It is only possible here to set down some of the
best shrubs available for the purpose, and to indicate, in a very
general way, the positions for which they are suitable.
Occasionally, where there is ample space, a deciduous tree of low growth
may be planted to great advantage. Not long ago, in a picturesque
district bordering on Western Germany, a mental note was made of the
excellent effect of Wild Medlar trees, scarcely more than good-sized
bushes, growing about the boulders and overhanging the edge of quarried
rocks. The white flowers in spring, and the fine form and tint of the
russet-brown fruit as it gradually swells during the summer months, give
this tree a peculiar claim on our attention where the position is
suitable. But in planning the main features of the Rock Garden, we
naturally turn our thoughts first to evergreen trees and shrubs, because
the plants grown in such positions, being usually either alpine or
herbaceous, are mostly in abeyance during the winter, and it is
desirable that the rockery, no less than every other part of the garden,
should be interesting even if it cannot be gay, during the period of
rest. A specimen Holly or, in exceptionally mild climates, a tall bush,
from 8 to 10 feet high, of _Pittosporum undulatum_, one of the most
beautiful of New Zealand evergreen trees, may be so placed, for example,
as to be exceedingly pictorial; but, as a rule, we must keep our shrubs
to an average maximum height of not more than from 4 to 5 feet, and,
generally speaking, those of still lower stature are better suited to
the ordinary Rock Garden.
[Illustration: _CISTUSES AND ROSES IN THE ROCK GARDEN._
(_In the left lower corner, Cistus hirsutus; middle, Rosa alba; to
right, R. rugosa Mme. Georges Bruant._)]
Some of the small-growing Conifers, from their compact habit and
distinct character, are especially well fitted to break the outline and
to give contrast. We think of Pines and Spruce Firs and Cedars as
majestic trees, and it is only when one comes to study them in their
manifold varieties that we find how many of these range from a height of
only a few inches to 3 feet, or at most to 4 feet.
Some species, it is true, do not lend themselves gracefully to the
dwarfing process, becoming clumpy and inelegant, but this charge cannot
be brought against many of the Cypresses and Junipers. Several of the
smaller Conifers, besides, give the advantage of distinct variations of
colour with the changing seasons. Reference is not now made to the
golden and silver forms, so-called, which occur in most of the genera,
and put on their brightest tints in spring, but to the deeper winter
colouring assumed, _e.g._ by the interesting _Retinospora ericoides_,
which alters its summer tone of dark green to purple brown on the
approach of cold weather; or by _Cryptomeria elegans_, a little less
hardy, which changes to a fine shade of bronzy crimson. Like other
plants, Conifers differ greatly as to constitution, and judgment must be
used in their choice. The dwarf alpine form of the Common Juniper
(_Juniperus communis nana_) is very hardy and slow-growing, never
becoming too rampant for the smallest Rock Garden, and shares the
blue-grey tint which is so characteristic of this beautiful species. _J.
c. alpina aurea_ is a delightful small-growing Conifer. In summer the
foliage is light yellow, and in winter heavily shaded with bronzy
yellow. Very distinct from it is the lovely prostrate Savin (_J. Sabina
procumbens_), one of the best of evergreen shrubs for the Rock Garden,
and one most restful and satisfying to the eye at all times in its deep
tones of sea green. A first-rate variety is _J. S. tamariscifolia_,
which is of very spreading growth.
[Illustration: _DWARF SHRUBS ON ROCK GARDEN._]
_Cupressus pisifera_, almost plumose in one of its many variations, and
_C. obtusa_, both better known perhaps under the garden name of
Retinosporas, are admirable, and may be used either in the normal or the
dwarf forms according to the greater or less space at command. Almost
the last tree, probably, which one would expect to see draping the
vertical face of a rock is the Spruce Fir, yet a weeping variety (_Picea
excelsa pendula_) is exceedingly effective in such a position as a foil
to hanging masses of richly-coloured Aubrietias or Golden Alyssum, while
it looks well at all seasons. Mention may here be made of a remarkable
Conifer, _Cunninghamia sinensis_, of great beauty and very distinct
character, which takes the shape, in our climate, of a spreading bush,
though in its native habitat it grows into a tree of noble dimensions.
It is suitable only for a Rock Garden of some boldness of construction,
and in gardens favoured with a mild climate and a sheltered position,
but under such happy circumstances a place should certainly be found for
this handsome and little-known China Fir.
Another uncommon coniferous shrub, also very distinct and more generally
useful than the last, is _Podocarpus alpina_. Though a native of
Tasmania, it grows at high elevations, and is able to resist severe
frost. Dark green in foliage, only about 2 feet in height, and of a
somewhat spreading nature, it is never out of place in the Rock Garden,
whether large or small.
From Conifers we may pass to Veronicas, certain of which might almost be
mistaken for some minute form of Cypress. Of this character is a small
group known in New Zealand, the natural habitat of a large number of
shrubby species, by the apposite name of Whipcord Veronicas. Being
themselves alpine, they are particularly well suited for grouping with
low-growing mountain plants. Six species or varieties of this
interesting section grow naturally at elevations ranging from 7000 to
4000 feet, and are much more hardy than is generally supposed. These
are: _V. cupressoides_, _V. c. var. variabilis_, _V. lycopodioides_, _V.
Armstrongii_, _V. Hectori_, _V. loganioides_.
The form of _V. cupressoides_, known as _variabilis_, was mistaken, on
its first introduction, for a distinct species, _V. salicornoides_, and
may still be met with under that name. The small violet or white flowers
of these miniature evergreen shrubs are not perhaps much to be taken
into account, but they have a distinct value of their own as rock-work
greenery. There are other dwarf New Zealand Veronicas of a leafy
character, differing essentially from these mimetic species, such as _V.
carnosula_ and _V. pinguifolia_, also inhabiting regions 5000 feet above
the sea-level, which are suited for localities with average advantages
of climate. Others again, such as _V. Lyallii_, _V. glauco-caerulea_,
and _V. hulkeana_, though they grow naturally at lower altitudes, and
must be reckoned only half-hardy, may yet be serviceable for Rock
Gardens on the southern sea-board, or on the west coast of Scotland.
Belonging to the larger-growing and more familiar species of Shrubby
Veronica, mention may be made of a good purple-flowered hybrid, of very
compact growth, known as Purple Queen, which is exceedingly ornamental
from its free-flowering habit. Many of the losses sustained amongst
these interesting New Zealand shrubs are owing to drought rather than to
frost, and their extreme susceptibility to dryness at the root is a fact
not recognised as it should be.
Hardy Heaths are of the utmost value in the Rock Garden, and range in
height from the 6 feet or more of _Erica arborea_ to the 6 inches of the
well-known _E. carnea_, and can be used in rough places, where more
delicate plants might not thrive. A sudden emergency once arose in the
experience of the writer, when a shelving mass of earth had to be
shored-up as quickly as possible with such material as lay ready to hand
at the moment. This happened to be found in a heap of ugly, yellowish,
water-worn boulders of great size, which abound in that particular
locality, at no great distance below the ground-level, and must be dug
out when any deep trenching has to be done. There was no time to be
wasted in facing the stones, which would have made them more sightly,
and they had to be used as they were. Fortunately a large consignment of
the best hardy Heaths had lately arrived from the Darley Dale Nurseries,
and were immediately seized upon to cover up the ugliness of the
hastily-built-up barricade. Boulders and Heaths, however, took to each
other kindly, in spite of a soil by no means specially suitable, and
with the addition, later, of a few good kinds of Cistus and other
shrubs, the bank still remains as happy a bit of rough planting as could
be desired.
Of the taller Heaths, _E. lusitanica_ is somewhat tender, and is not so
generally useful as _E. mediterranea_ or _E. arborea_ (Tree Heath). A
hybrid form--_E. mediterranea x E. carnea_--is excellent, and comes into
flower about Christmas, in advance of either of its parents, when its
pale-purple spikes are very welcome, and are quite distinct from the
rosy-red flowers of _E. carnea_: it is known as _E. mediterranea
hybrida_. The foliage of hardy Heaths is never unsightly, but the
persistent dead flowers are, and these should always be clipped off as
soon as their beauty is over, or the new growth will break away above
the withered flowers, leaving, in many cases, straggling and unclothed
branches. The omission of this needful work every season is a fruitful
source of the raggedness which brings some discredit on these otherwise
attractive plants.
Many flowering shrubs of the same natural order as Heaths, but unlike
them in general appearance, such as the Alpine Rhododendrons, _R.
ferrugineum_ and _R. hirsutum_, and the less well-known but very
beautiful and distinct _R. racemosum_, as well as some of the miniature
varieties of _Azalea indica_, notably _R. obtusa_ and its forms, seem
peculiarly suitable for the Rock Garden (see p. 428 for lists of the
best Rhododendrons). Again, where rock meets more level ground, and the
trickle of a stream can be so directed as to give moisture without
sogginess, a considerable number of peat-loving evergreen shrubs
belonging to the same order, of the type of _Gaultheria_, _Vaccinium_,
and _Pieris_, may be used with excellent effect. _Gaultheria Shallon_,
indeed, is a singularly fine shrub in any position, and is not very
exacting in any of its requirements. Growing about 2 feet high, with
purple leaf-tints in winter, and spikes of white waxy flowers, brightly
tinged with red, in spring, which are followed by purple fruit, few
things can surpass it in its way. For carpeting moist spots, the little
_G. procumbens_, which rises scarcely 3 inches from the ground, will
fill a useful place with its winter colouring of crimson brown. Shrubs
of this class are well worth study by those whose locality admits of
their cultivation.
For dry, sunny, and stony banks Rock Roses may be chosen, but the
position must be wind-screened, a more important factor in the question
of their hardiness than cold. The large-growing Gum Cistus is well known
and tolerably hardy everywhere, and so also is _C. laurifolius_, but
there are several most desirable species of dwarfer growth, such as the
white, crimson-spotted _C. lusitanicus_, the pink-flowered _C.
villosus_, the bright-red _C. crispus_, and the pure white _C.
florentinus_, which are quite happy in sheltered rock walks especially
by the sea; they have been also grown with success in many colder
situations inland. The Cistineae, at best, are somewhat short-lived, and
lose vigour and power of resistance as they grow older. Keep up,
therefore, young, thrifty stock by yearly cuttings to fill up inevitable
gaps, which is a matter of no cultural difficulty. Where Rock Roses are
out of the question, their place may worthily be filled by the hardier
shrubby _Helianthemums_, though they differ greatly from Cistineae in
their trailing habit and smaller flowers. The breadths of brilliant
colour given by these Sun Roses while in bloom are invaluable, and may
be enjoyed to the full in almost any locality, while the many variations
of tint, from deep green to ashen grey, in their leafage should also be
taken into consideration, as it increases their usefulness when out of
flower.
No list of good shrubs for the Rock Garden would be complete without
some reference to _Yuccas_, which for all practical purposes must be
included under that head. Groups of these magnificent plants, with their
sub-tropical effect, cannot be surpassed for nobility of outline and
stateliness of flower. To do them full justice, they must have space to
develop their grand proportions, but this may often be found on the
ridge or upper slope, even in rock-work of limited character. _Y.
gloriosa_, with its fine form, _Y. recurva_, and the stemless _Y.
flaccida_, of smaller growth, are amongst the best and hardiest kinds,
and to these may be added _Y. angustifolia_, another valuable and nearly
stemless species.
It is only possible, in restricted space, to touch in a very cursory way
upon a few of the available groups of dwarf-growing shrubs. Many more
than have been mentioned will occur readily to the minds of those who
are at all conversant with plants, such as _Abelia rupestris_, _Magnolia
stellata_, several beautiful species of _Daphne_, some of the St. John's
Worts, of low-growing _Cytisus_, and others which may be classed under
the head of miscellaneous. The subjoined list, though it does not
pretend to be exhaustive, will be found of use, either for purposes of
winter greenery or for summer embellishment, by those who are seeking
good and suitable dwarf shrubs for planting, under varied conditions in
the Rock Garden.
DWARF SHRUBS FOR THE ROCK GARDEN
HARDY EVERGREEN
Buxus sempervirens vars.
Cotoneaster buxifolia.
Danaea Laurus (Alexandrian Laurel). Syn. Ruscus racemosus.
Gaultheria procumbens.
Lavendula vera (Lavender).
Mahonia (Berberis) Aquifolium.
Osmanthus Aquifolium.
Pernettya mucronata.
Rosmarinus officinalis (Rosemary).
Skimmia Foremani.
Veronica (Whipcord).
,, cupressoides.
,, cup. var. variabilis.
,, Armstrongii.
,, Hectori.
,, loganioides.
,, lycopodioides.
_Conifers_
Cupressus obtusa nana.
,, ericoides.
,, thyoides.
Juniperus communis nana.
,, Sabina prostrata.
Picea excelsa clanbrassiliana.
,, ex. pumila glauca.
Podocarpus alpina.
HARDY FLOWERING SHRUBS
Azalea (Rhododendron) amoena.
,, indica and vars.
,, mollis.
Cytisus Ardoini.
,, Kewensis.
,, purpureus.
,, Shipkaensis.
Daphne blagayana.
,, Cneorum.
,, Mezereum.
Dryas octopetala.
Erica carnea.
,, ciliaris.
,, lusitanica.
,, mediterranea.
,, m. hybrida.
Genista germanica.
,, pilosa.
Helianthemum vars.
Hypericum moserianum.
,, olympicum.
,, patulum.
Kalmia angustifolia.
,, glauca.
Magnolia stellata.
Olearia Haastii.
Ononis rotundifolia.
Philadelphus microphyllus.
Phlomis fruticosa.
Polygala Chamaebuxus and var. purpurea.
Prunus nana.
Rhododendron ferrugineum.
,, hirsutum.
,, racemosum.
Rosa lutea.
,, pimpinellifolia.
,, xanthina (Ecae).
Rubus arcticus.
Spiraea arguta.
,, Bumalda.
,, decumbens, &c.
,, Thunbergi.
Veronica buxifolia.
,, carnosula.
,, pinguifolia.
,, linifolia.
Yucca angustifolia.
,, filamentosa.
,, fil. var. flaccida.
,, gloriosa.
,, recurvifolia.
FLOWERING AND OTHER SHRUBS FOR SHELTERED SITUATIONS AND MILD CLIMATE
Abelia rupestris.
Cistus albidus.
,, crispus.
,, lusitanicus.
,, villosus.
Coronilla Emerus.
,, glauca.
Daphne Dauphini.
,, Genkwa.
Fabiana imbricata.
Escallonia macrantha.
,, philippiana and hybrids.
,, rubra.
Eugenia Ugni.
Fatsia japonica (Arabia Sieboldi).
Grevillea rosmarinifolia.
Helianthemum formosum.
Linum arboreum.
Myrtus communis.
,, box leaved.
Olearia dentata.
Ozothamnus rosmarinifolius.
Philesia buxifolia.
Pittosporum Tobira.
,, undulata.
Rhododendron (see pp. 137 and 424).
Rosa simplicifolia.
Rubus rosaefolius.
Swainsonia alba.
Trachycarpus (Chamaerops) excelsa (Chinese Fan Palm).
Veronica chathamica.
,, epacridea.
,, Fairfieldii.
,, glauco-caerulea.
,, pimeleoides.
,, speciosa.
,, Traversii.
,, Purple Queen (hyb.).
_Conifers_.
Cryptomeria elegans.
Cunninghamia sinensis.
[Illustration: _ONONIS FRUTICOSA (Shrubby Rest Harrow) AT EXETER._]
FOR MOIST PEATY SOIL AT THE FOOT OF ROCKS
Andromeda polifolia.
Bryanthus erectus.
Cassandra calyculata.
Cassiope tetragona.
Daboecia polifolia (Irish Heath).
Gaultheria procumbens.
Ledum palustre.
Leucothoe axillaris.
,, Catesbaei.
Myrica asplenifolia.
,, Gale.
Pieris floribunda.
,, japonica.
Rhodothamnus Chamaecistus.
Salix reticulata.
Vaccinium crassifolium.
,, uliginosum.
,, Vitis-idaea.
Zenobia speciosa var. pulverulenta.
[Illustration: _TREE IN COURSE OF REMOVAL WITH ONE OF BARRON'S
MACHINES._]