Common Alder, with its many varieties--Cut-leaved, the Golden-leaved, and such as _Alnus incana_ and _A. serrulata_.

_Taxodium distichum_ (Deciduous Cypress); tender green in spring and brownish red in autumn, when the leaves change colour.

_Hippophae rhamnoides_ (the Sea Buckthorn).

[Ill.u.s.tration: _NATURAL TREE GROWTH BY WATER (Burnham Beeches.)_]

TREES AND SHRUBS FOR MOIST (BUT NOT SWAMPY) SOIL

_Berberis Darwinii_ (Darwin's Barberry), _B. Thunbergi_ (for its beautiful autumn leaf-colouring), Birch, Dogwoods, _Cornus alba_ and varieties; the variety _sibirica_ has brilliant-red stems. _Cotoneaster buxifolia_, _C. frigida_, _C. Nummularia_, _C. Simonsii_; Ash, _Myrica Gale_ (Sweet Gale) and _M. asplenifolia_; _Ledum pal.u.s.tre_, _Nyssa sylvatica_ (Tupelo tree), Mountain Ash, _Quercus aquatica_ (Water Oak), _Q. pal.u.s.tris_ (Swamp Oak); _Rhamnus Frangula_ (Buckthorn). Roses with brightly-coloured hips--_Rubus biflorus_ (White-stemmed Bramble), _R. fruticosus fl. pl._ (Double Pink Bramble). _R. laciniatus_ (Cut-leaved Bramble), _R. spectabilis_ (Salmon Berry). _Sambucus racemosa_ (Red-berried Elder), _Spiraea Douglasii_, _S. hypericifolia_, _S. lindleyana_; Tamarisk. _Viburnum Opulus_ (Guelder Rose); when this native shrub is weighed down with the rich red berry-cl.u.s.ters, it is a remarkable colour picture, and the autumn leaf tints add to its beauty.

Of Conifers, mention may be made of _Tsuga canadensis_, _Picea sitchensis_, _Cupressus thyoides_, and _Thuya gigantea_.

Bamboos: Select those of robust growth, such as _Arundinaria j.a.ponica_ (_Bambusa Metake_), _A. Simoni_, _A. Veitchii_, and _A. palmata_; _Phyllostachys viridi-glaucescens_ and _P. mitis_.

[Ill.u.s.tration: _WILLOWS BY WATERSIDE._]

CHAPTER XIX

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 s.p.a.ce, 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 circ.u.mstances 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 s.p.a.ce, 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.

[Ill.u.s.tration: _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 a.s.sumed, _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 const.i.tution, 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 proc.u.mbens_), 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.

[Ill.u.s.tration: _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 s.p.a.ce 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 ma.s.ses 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 n.o.ble 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 circ.u.mstances 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 pa.s.s 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 alt.i.tudes, 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 ma.s.s of earth had to be sh.o.r.ed-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 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 surpa.s.s it in its way. For carpeting moist spots, the little _G. proc.u.mbens_, which rises scarcely 3 inches from the ground, will fill a useful place with its winter colouring of crimson brown. Shrubs of this cla.s.s 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 leaf.a.ge 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 surpa.s.sed for n.o.bility of outline and stateliness of flower. To do them full justice, they must have s.p.a.ce 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 s.p.a.ce, 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 cla.s.sed 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 proc.u.mbens.

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.