Chapter 4. Dwarf Flowering And Ornamental Shrubs And Trees For The Rock Garden

Dwarf shrubs play a very important part in the composition of the rock garden, but many people neglect them, for they fail to realize the value of a few well-placed specimens. Dwarf shrubs are planted in the rock garden for several reasons; they may be used as a background and to break the skyline; they serve to accentuate the appearance of height or depth: for this purpose they are generally placed on a summit, on a ridge, or in some other prominent position; in exposed situations they may be used to provide shelter; by no means their least useful function is to relieve drabness and monotony in winter.

Happily there are dwarf representatives of almost all genera and species, both evergreen and deciduous; and we have ample choice of colour, form, and flower. Especially adapted to this use are the dwarf conifers, in view of their beauty of form, most noticeable when they stand out almost alone in winter. Another class extremely valuable for the rock garden are the small ericaceous, or heath-like, shrubs. Many are prostrate or of trailing habit and will furnish a variety of beautiful colour throughout the year. In spring, summer, and autumn we may choose from a plethora of dwarf flowering shrubs, both evergreen and deciduous.

These dwarf shrubs may be divided into two main classes: those of a prostrate and trailing nature that are used as ordinary rock plants to clothe the rocks, and those of rounded or pyramidal growth that serve, as explained above, to bring variety and contrast to the contours of our rock gardens.

Planting

Before planting, the ground should be deeply dug or trenched to a depth of two feet, enriched with well-rotted old manure and leaf-mould, and sufficient space should be allowed to each individual plant for the free and full development of its own peculiar habit of growth. The turf within a radius of one to two feet round bushes planted in grass should be permanently removed so that the earth may be thoroughly broken up and exposed to the air.

As a general rule, plants of medium size for their kind should be planted rather than fully-grown specimens. They more readily take root and the proportion of losses is much smaller. When there is no hurry and when planting is done with an eye to an effect which is to be produced several years later, it is often wise to plant even younger bushes. In this case it is possible either to fill the space with small bushes and to remove a proportion when they become overcrowded, or each shrub may be allotted the full space it will require in later years, the bare soil in between being temporarily decorated by other plants. Usually the best time to plant deciduous shrubs is from the middle of October, when the leaves begin to fall, to the middle of November, or in Februrary and March. Evergreens are best planted in September and early October, or better still, perhaps, in April and the beginning of May. Never plant evergreens in the depth of winter when their vitality is at the lowest, nor when cold, drying winds are prevalent.

Plants that have been grown in pots may, of course, be planted out at almost any time during the year. In the case of both deciduous and evergreen shrubs it is usually wise, at the time of planting, to thin out and reduce the length of the branches by about one-third; this will somewhat relieve the strain put upon the roots, at this time themselves considerably reduced.

The position is prepared by digging out a hole about two feet in diameter, and one foot in depth, in ground that has been well drained. The shrub or tree should be placed upright in the centre of the hole and the lowest roots should be laid out horizontally. Fine earth should then be loosely thrown over them, and pressed down firmly. The next layer of roots, should be treated in a like manner, and so on until the whole of the roots are covered. It is most important that the rootlets should, as far as possible, assume their natural position, thoroughly penetrating and permeating the surrounding soil. It is also most important to make the soil firm at each stage of the planting, in order to minimize the depth to which the shrub will sink.

Firm planting is necessary in any soil, and in light land it may be necessary to use a rammer. Shrubs should be planted to about the same depth as in the nursery garden; this depth can be seen from the marks on the stem.

Grouping And Arrangement

The arrangement of shrubs naturally varies according to the purpose which they are to fulfil. If they are to serve as individual specimens in the rock garden, clearly no "arrangement" is required. If planted in groups to form a background or shelter, it is usually desirable that several plants of a kind should be placed together; though even here full space should be allowed for each individual plant to develop. This grouping together of, say, three to half a dozen specimens, is not only more effective than scattering single plants about indiscriminately, but it makes it easier to give each group of shrubs the special soil in which they thrive best. (For soils suitable to each species, see the Alphabetical List of Plants.) The fact that we can have a continued sequence of bloom from flowering shrubs almost all through the year, provided they are carefully selected, is often overlooked. It is necessary, therefore, to select shrubs not only for the colour of their flowers, their suitability for their situation, but also for the time of year at which they flower. Care must be taken that specimens whose colours clash and which bloom simultaneously are not placed together. Associate shrubs whose blooms harmonize in colour and time of flowering, and allow the blooms of the specimens in flower to be set off and enhanced by the foliage of shrubs whose flowers are over or still to come.

The stronger-growers must be kept in check by periodical pruning or they may overpower the more beautiful but perhaps less vigorous plants.

When planting shrubs as backgrounds, too great a regularity is to be avoided, and care must be taken to see that they do not present a straight, forbidding line. Rather should they afford projections and bays: now running forward into the rock garden, now forming sheltered recesses in which plants may find welcome shade and protection. During the summer the soil round the shrubs should be kept well hoed and should be forked over each winter, except in the case of Rhododendrons, Azaleas, etc., these requiring a mulching of well-rotted leaves or peat. Where a shrub is seen to be doing badly or to be exhausted, well-decayed manure should be thoroughly worked into the soil round the roots.

Dwarf Conifers

These are all handsome trees, and among them will be found many species and varieties that may well be planted singly in prominent positions in the rock garden.

A list of the best dwarf conifers will be found below.

Shrubs With Coloured Foliage In Autumn

In planting dwarf trees and shrubs it is well worth while to consider their appearance, not only in the spring and summer, but in the autumn and winter also; for when the garden is at its most sombre, trees and shrubs, if suitably chosen, will provide notes of cheerful and striking colour.

Pruning Shrubs

The time for pruning depends on the season of flowering, and the method of pruning is dependent upon whether the bloom is borne on the new or the old wood. Where the new shoots, that is to say those of the current year, bear the flowers, some of the old and weak growth has to be cut in order that the new shoots may be encouraged. This may be done any time from October to November, as the flowers are usually borne in late spring or early summer. Where, however, the plants flower on the old wood, generally in late winter or early spring, only the decayed and useless old wood must be cut away, which is usually done in late spring or early summer directly after flowering, as it is of vital importance to give the plants as much time as possible to form and ripen new wood before the winter sets in, for on this wood the flowers will be borne the next spring. Many such plants are only pruned sufficiently to keep them tidy and trim.

April is the best time to trim evergreens, except conifers, which are best trimmed in September or October. Conifers, however, save when grown as hedge-plants, are not usually pruned. When such conifers as the cupressus or yew are used as hedges, they can be pruned back to any height desired; the lateral branches also being trimmed in.

The aim of pruning is, first, to let air and light to the wood so as to ripen it and thus encourage bloom on flowering shrubs; secondly, to train the plant into the shape and size required; and thirdly, to keep it tidy. There are also several ways of pruning, the most usual being the cutting back of the shoots. Side shoots are often "spurred" or cut right back, leaving only three or four buds; plants requiring this treatment are usually late-flowerers. Again, the strong main shoots may be "topped" or cut back by about one-third to encourage sturdy growth, or may be only just "tipped" to keep the plant tidy and the growth within bounds; at the same time all old and weak wood is cut out. Another method of pruning, often required, is the removal of the seed-heads from such plants as the rhododendron. If these seed-heads are allowed to remain in position, a poor crop of bloom will result in the following year. Disbudding, the removal of superfluous buds, is also looked upon as pruning, for it increases the size of the flowers.

More or less tender shrubs grown in the open in sheltered positions should never be pruned in autumn. This would lay them open to attacks by frost; they should be pruned in April, or even later, when danger of severe frosts is past.

The reader is referred to the Alphabetical List of Plants for full instructions for the pruning of each kind.

Propagation Of Shrubs

Seeds. Seeds saved from the garden should not be gathered too early, but must be allowed ample time to ripen, and should be cleaned before being sown. The seeds of most shrubs are best sown under glass, in well-drained boxes of sandy soil, in February or March, and when germinated and sufficiently high, should be thinned out to one and a half to two inches apart; the less hardy kinds being hardened-off in a cold frame and the hardy kinds planted out in nursery beds in the open. The seeds of most shrubs and trees germinate in a month or two; some, however, like the rose and thorn, take a year and even more. The seeds of most conifers must ripen in their cones on the trees for about a year, some require to hang for quite two years. When the cones have been gathered, they are stored in a warm and dry place. The dryness opens the cones and the seeds are liberated, and should be sown thinly in the open in March or April. They should be only just covered with fine sandy soil, seeds from healthy trees only being used. Transplant from the seed-beds to rows in the nursery garden as soon as the seedlings are large enough to handle, usually from one to two years after sowing. It is wise to shelter the young seedlings from the sun and from the frost in winter.

Chamaecyparis Lawsoniana Pygmaea Argentea Thuja Plicat Aurea Rogersii

[Ward Lock Juniperus Communis Compressa Chamaecyparis Pisifera Squarros/! Intermedia

Cuttings. This is undoubtedly the most popular method of propagating shrubs. It provides larger plants in a much shorter time, and ensures that the new plants shall be true to type, which cannot always be relied upon when raising from seed. This method is resorted to especially when propagating dwarf, variegated, or rare shrubs. Strong, sturdy shoots varying from three to twelve inches in length should be taken. During the spring, summer, and autumn most shrub cuttings may be struck in the open, except the cuttings of most conifers, and many other evergreens which always require the protection and moist atmosphere that glass provides. Cuttings inserted in the autumn remain inactive through the winter, and do not usually form roots until the following spring. They must, therefore, not be disturbed until the next autumn, when they may be planted-out twelve to eighteen inches apart in a nursery bed.

There are a number of proprietary articles from which solutions may be made to help in the propagation of the more difficult cuttings.

Division of Roots. All the so-called "tufted" herbaceous shrubs, or those that throw out suckers from their crowns or base, may be propagated by division of roots at the time of year when they are best transplanted.

Grafting or Budding. If the shrubs are grafted, this is usually carried out under glass between January and early June, but many of them may be grafted in the open in April and May. Budding is usually effected in the open in July and August.

Layering. This method is usually employed in the spring or early summer.

The reader is advised to consult the Alphabetical List of Plants, Chapter 12 where he will find the best methods of propagating each individual shrub. Here also will be found full cultural details.

See also Propagation of Plants, Chapter 7.

Dwarf Shrubs For The Rock Garden

Rounded, Pyramidal, and Erect Growth

Abelia chinensis, etc.
Acer pulmatum vars.
Artemisia abrotanum
Azalea (some vars.)
?Berberis (various)
Betula nana, etc.
?Bryanthus erectus
Cassinia fulvida
Chamaecyparis (vars.)
Cistus crispus, etc.
?Cornus canadensis, etc. Corokia cotoneaster Cryptomeria (vars.) Cydonia Maulei Cytisus nigricans, etc. ?Daphne (various)
Deutzia discolor, gracilis, etc. Fuchsias (some vars.)

Garrya elliptica
Genista dalmatica, horrida, etc.
Hypericum (various)
Lonicera fragrantissima
Magnolia stellata
Olearia myrsinoides
Ononis fruticosa
Osmanthus Delavayi
Philadelphus microphyllus, etc.
Potentilla davurica, etc.
Rhododendrons (dwarf vars.)
?Rubus australis
Salix herbacea, retusa, etc.
Santolina incana
Senecio laxifolius
Spiraea bullata, etc.
Thuja (dwarf vars.)
t*Viburnum Carlesii, etc.

Heath-like Lime Haters

Andromeda polifolia
Bruckenthalia spiculifolia
Calluna vulgaris and vars. Alportii, aurea, Foxii, and numerous others
Cassiope tetragona Daboecia polifolia Erica (most vars.)
*Gaultheria procumbens, nummul-arioides, etc.
Hypericum Coris, cuneatum, etc.

Kalmia (various)
Ledum latifolium and L. palustre Leiophyllum buxifolium
?Pernettya (various)
Polygala Chamaebuxus Rhododendrons (various)
Spiraea procumbens, etc.
Vaccinium Vitis-idaea
Veronica loganioides
Zenobia speciosa pulverulenta

Trailers and Prostrate Shrubs

* Cotoneaster adpressa, congesta, humifusa, thymifolia
Cytisus Ardoinii, Beanii, etc. ?Daphne Cneorum, etc.
Dryas octopetala, etc.
?Gaultheria procumbens, etc. Hedera

Helianthemum
Hypericum reptans
Juniper Sabina, communis nana
Linnaea borealis
Polygonum vaccinifolium
Salix arbuscula, herbacea, and retusa

?Denotes best Berry-bearing Shrubs.

Coloure4 Foliage in autumn.

Moisture-Loving Trees And Shrubs

Conifers (Dwarf)

Abies balsamea, var. Hudsonia, A. pectinata, etc.
Cedrus atlantica aurea, C. a. fasti-giata, C. a. glauca, etc.
C. Deodara, var. pendula
C. Libani brevifolia
Crytomeria japonica nana, C. j.spiralis, C. j. Vilmoriniana Chamaecyparis (syn. Cupressus)
Lawsoniana Ellwoodii
C. Lawsoniana argentea compacta,glauca, etc.
C. obtusa nana
C. pisifera, var. squarrosa
C. thyoides, var. ericoides

Juniperus chinensis procumbens, J. c. aurea, J. c. Pfitzeriana, J. com-munis depressa, J. c. aurea, J. Sabina, J. recurva, J. r. squa-mata
Picea excelsa conica, P. e. compacta, P. e. dumosa, P. e. globosa nana
Pinus (densiflora, var. aureovariegata,P. montana, var. pumilio
Taxus baccata ericoides, etc.
Thuja dolobrata nana, T. occidentalis conspicua, T. o. Ellwangeriana,T. o. Rheingold, etc.

*Denotes best Berry-bearing Shrubs.

Coloured Foliage in autumn.

Are You Ready To Move Onto The Next Lesson? Click Here...