A shrub may be defined as a perennial woody plant, branching naturally from its base without a defined leader (a single main shoot), and not normally exceeding 10m (30ft) high. Shrubs may be deciduous or evergreen and range from plants no more than 3-5cm (1-2in) high, such as some heaths and creeping willows, to huge rhododendrons. Some woody plants may grow either as large shrubs or trees according to circumstances. When the lower part of the plant is woody and the upper shoots are soft, it is referred to as a sub-shrub.
Preparation of the site
Just because shrubs are so easy to grow, it is a mistake to imagine that you can just stick them into a hole in the ground and then leave them to their own devices. Proper and careful planting is one of the most important operations contributing to their successful cultivation.
The initial preparation of the site should be done, whenever possible, a few months before planting is due to be carried out, in order to give the soil ample opportunity to settle. This may not always be possible, in which case a certain amount of raking and treading may be necessary on light sandy soils, while on heavier clays extra precautions will have to be taken to avoid leaving air pockets round the roots.
Deep and thorough cultivation, either by trenching or double digging, to break up the subsoil, as well as the top spit, is the ideal to be aimed at.
Although the roots of the shrubs will eventually travel far in search of nourishment and moisture, this preliminary cultivation will ensure that they get away to a good start in their first season.
Before the shrubs are put in, the surface soil should be broken down to a reasonably good tilth. Getting it into this condition will provide an opportunity of raking in a slow-acting organic fertilizer, such as steamed bone flour, meat and bonemeal or fish manure. Any of these, applied at the rate of 80-110g (3-4oz) per sq m (sq yd) should provide adequate reserves for the first growing season.
With a new garden, on former pasture or woodland, the chances are that the soil will already contain sufficient humus. First, the turf should be sliced off and placed at the bottom of the second spit or, as far as woodland sites are concerned, all fallen leaves, leafmould, etc, should be collected up and incorporated in the soil as digging progresses.
Where existing beds and borders are being given over to shrubs, it may be necessary to provide humus-forming materials in the form of sedge peat, leafmould, garden compost, spent hops, or rotted down straw, when the site is prepared.
Whether a single specimen shrub is being planted, or hundreds of shrubs are set for a hedge, the actual planting process must be carefully carried out if the plants are to give of their best. Planting holes must be large enough and deep enough to accommodate the roots without bunching or overcrowding, and it is a good idea to leave a slight mound at the base of the hole on which the plant can rest while the roots are spread out and soil is worked among them. On light sandy soils this latter procedure will be simple, but with sticky clays, particularly if planting coincides with a wet spell, it may be necessary to fill in the holes with compost or dry sifted soil. Most shrubs will benefit by being planted in a mixture consisting of equal parts of sifted soil, peat or leafmould and bonfire ash.
Many evergreen shrubs, including rhododendrons, will arrive from the nursery with their roots ‘balled’ in sacking. When these are planted, the root ball should remain intact. It is not even necessary to remove the sacking, as it will soon rot away, but if it is left in position it is advisable to cut the ties that secure it round the plant.
The shrub should be gently jiggled up and down to ensure that all the roots are in contact with the soil and to prevent air pockets. Planting is usually a job for two—one holding the shrub in position and giving it an occasional shake, the other working the soil round the roots and firming it with the boot, or where small shrubs are concerned, with the hands.
Depth of planting is important.
The soil mark on the stem made at the nursery can be used as a guide and shrubs should be planted with the soil slightly above this to allow for the slight sinking that is likely to take place.
Normally, staking will not be necessary, although in positions exposed to strong winds it may be advisable to provide a temporary support for the first season to guard against root damage from wind rock. In any case, it is always advisable to go round newly planted shrubs after a spell of rough weather or prolonged frost to refirm the soil round the base.
The best time to do this is after the soil has had a chance to dry out. Although they like firm planting no shrubs like their roots encased in soil that has been consolidated into a concrete-like consistency, which is what will happen if an attempt is made to firm heavy clay soils when they are still waterlogged.
There are two schools of thought where the initial planting of a new shrub border is concerned. Some garden writers advocate planting at distances sufficient to allow each shrub to develop to its fullest capacity without overcrowding. Others advise planting well in excess of the final requirements and later ruthlessly sacrificing any that are not required.
There are drawbacks to each of these methods. In the latter instance, although it is easy to see when shrubs are beginning to exceed their allotted space above ground, it is difficult to say when overcrowding of the roots starts to take place. Waiting till the branches are jostling one another may cause considerable damage to the roots of those that remain when the unwanted surplus is removed.
On the other hand, in a shrub border with every plant at a distance from the others sufficient to allow room for the ultimate spread of its roots there will be plenty of wide open spaces for several years to come. These can be filled during spring and summer by bulbs and perennials.
The best solution is to provide temporary stopgaps in the form of relatively short-lived shrubs, or common ones of vigorous habit that will not be greatly missed when the time comes to get rid of them to make room for the more permanent occupants of the border.
Brooms are ideal for this purpose. No matter how carefully they are pruned they invariably become leggy and untidy in the course of four or five years. But in their prime they make a colorful display. The many lovely hybrid forms of the native broom, Cytisus scoparius, range from white through every shade of cream and yellow to rich mahogany reds and purples. A good representative selection would include ‘Cornish Cream’, ‘Dorothy Walpole’, a rich crimson, ‘Lady Moore’, a bicolor with rich red wings and keel, the lovely apricot and buff ‘C. E. Pearson’ and the dainty carmine and rose-red ‘Johnson’s Crimson’. For the edge of the border or the rock garden there are the early-flowering C. praecox and the prostrate
C. x kewensis both of which bear masses of cream colored blossom.
Other ‘expendables’ include the flowering currants, some of the more rampant mock oranges, such as Philadelphus coronarius, as well as the taller forsythias and such coarse-growing shrubs as Buddleia davidii.
Winter flowering shrubs
By judicious planning and selection, it should be possible to have shrubs in flower throughout the year. Winter-flowering shrubs make an invaluable contribution to our gardens, bringing color and, in many instances, penetrating fragrance during the darkest days of the season.
By mid-November, when the early heavy frosts have stripped the deciduous shrubs and trees of most of their leaves, the first pinkish-white flower clusters of Viburnum fragrans will be starting to open. This is one of the loveliest and most useful of winter shrubs; it continues to produce relays of richly fragrant blossoms right up to the end of February. There is a white variety, candidissima, with flowers lacking the pinkish tinge of the type, but which contrast even more effectively with the bare, cinnamon-brown twigs.
The witch hazels start to flower towards the end of December and in most seasons it is possible to fill a vase with their curious spidery, cowslip-scented blossoms at Christmas. Hamamelis mollis, the Chinese species, with showy golden-yellow flowers—showy by winter standards, at any rate, is the one most widely grown. The form brevipetala has shorter petals of orange, while those of pallida are a pale sulphur-yellow.
H. japonica comes into flower a little later ; the blooms of this species are more striking, their golden yellow strap-like petals being set off by a purple calyx. They lack, however, much of the scent of the mollis varieties.
More fragrant still—half a dozen small sprigs will scent a room—is the winter sweet, Chimonanthus praecox, with waxy, pale yellow flowers, the centres blotched with purple. In the variety grandiflorus they are of a pure clear yellow. The plant type starts to bloom in December, the flowers of the latter open a few weeks later and sacrifice some of their scent for showiness.
February will see the bare branches of the mezereon, Daphne mezereum, covered in purple, hyacinth-scented blossom. This is a short-lived shrub and might well qualify to fill gaps in the border if it did not make such a valuable winter contribution to the garden. Fortunately, fresh supplies come easily from seed, and provided the scarlet fruits—which incidentally are extremely oisonous—are protected from the birds, which are very partial to them, the task of providing replacements is a simple one as the seed will germinate freely in any good garden soil.
From spring to summer the main display starts with shrubs such as the viburnums, brooms and lilacs and reaches its zenith at midsummer.
With the many plants to choose from, planning and planting for continuity of display should be easy. To obtain a lavish display of blossom for as long as possible it will be necessary to include in the planting plan shrubs such as Caryopteris clandonensis, and the tree hollyhock, Hibiscus syriacus, the flowering season of which covers the months of late summer and autumn.
Lilacs rank among the favorite shrubs of late spring and the most decorative are the hybrids of Syringa vulgaris. Among both singles and doubles, old favorites still reign supreme, with ‘Souvenir de Louis Spath’ as the best purple and ‘Maud Notcutt’ most popular as the most outstanding single white. Lesser-known single forms include ‘Esther Staley’, an unusual shade of pale lilac verging on pink, and ‘Maurice Barnes’, the best examples of the true ‘lilac’ color.
Many prefer the doubles with their chunky tightly-packed conical flower trusses, although they lack some of the elegant form of the singles. ‘Katherine Havemeyer’ (soft mauve), ‘Madame Lemoine’ (white) are all established favorites. All of them, both single and double have the typical enchanting perfume of lilacs and are vigorous shrubs, reaching a height of 5-6m (1520ft).
In the smaller garden there will not be much room for these giants, but some of the lilac species are much more compact and would prove useful where space is restricted. Their flowers may be smaller and less showy than those of the larger hybrids but they yield nothing to these where fragrance is concerned. Syringa macrophylla, for example, makes a dainty shrub, only 1-2m (4-6ft) in height, with elegant purple flower spikes that are extremely fragrant and have an attractive habit of continuing to bloom at intervals throughout the summer. S. persica alba, a white-flowered form of the incorrectly-named Persian’ lilac is a delightful Chinese shrub with narrow leaves and handsome panicles of white flowers.
In late spring the shrub border is redolent with fine perfumes. The mid-season viburnums, with their distinctive clove scent will be in bloom then; also V. x burkwoodii, a vigorous cross between V. carlesii and V. utile, with its large globes of white, V. x carlcephalum, another carlesii hybrid, with in this instance, V. macrocephalum as the other parent, whose large fragrant flowers measure 10-15cm (4-5in) across and V. carlesii itself, still ranking as one of the most popular garden shrubs.
Philadelphus, or mock orange, often wrongly called syringa, will be among the next batch of favorites to come into flower. Its fragrance can be cloying and is too heavy for some tastes. In many of the newer varieties, however, the somewhat funereal smell of P. coronarius, is more subdued, and the superb decorative value of their white flowers could never be in dispute. For the smaller gardens of today, there are a number of compact hybrids, much less coarse inhabit than the once-popular P. coronarius. ‘Enchantment’ is one of the loveliest of these, with elegant, arching branches thickly festooned with double white flowers in June and July. Manteau d’Hermine’, only 1.3m (4ft) tall at maturity, also produces its double white blossoms freely. `Sybille’, another delightful shrub of modest dimensions, bears an abundance of dainty white, purple-scented blooms. P. microphyllus can be particularly recommended for the small garden. Its leaves are very small and the unusual four-petalled flowers have a distinctive fruity perfume.
Weigelas, still listed sometimes as Diervilla, are useful midsummer shrubs of medium height and girth. Their flowers, borne along the entire length of the previous years’ shoots are long and tubular, rather like miniature foxgloves. W. Florida, a native of Korea and northern China, was discovered by Robert Fortune in the garden of a Chinese mandarin in the last century; it is the hybrids of this attractive species that have produced our popular garden forms.
`Feerie’, W. vanhouttei and W. styriaca are all good, with flowers of varying shades of pink. ‘Eva Rathke’ and ‘Bristol Ruby’ have flowers of a stronger color. ‘Eva Rathke’ has the longest flowering season. Its deep crimson flowers appear from mid-May until August.
Deutzias, shrubs that deserve wider recognition, will also be in flower at this period. Their habit of growth, narrow at the base but arching elegantly outwards when they attain a height of 1-2m (4-5ft), makes them invaluable where ground space is at a premium. The flowers, which are like small tassels, are profusely borne, while in winter the bare cinnamon branches are of great decorative value. D. elegantissima is the form most commonly encountered. The pinkish-purple blossoms are profusely borne on arching sprays, while in the variety pulchra they are a pearly pink. `Codsall Pink’ is a strong grower and can reach a height of 3-5m (10-15ft). This form flowers later than most, starting at the end of June and continuing into July.
No shrub garden would be complete without the summer-flowering viburnums. The snowball bush, V. opulus sterile, is the most popular of these. Its globular flowers, green at first, but turning pure white later, make an established specimen of this lovely summer shrub an unforgettable sight when the branches are smothered in white snowballs. It is, however, rather a vigorous grower for small gardens and for these V. tomentosum plicatum would be a more appropriate choice. This seldom exceeds 2m (6ft) in height and the ‘snowballs’ are in the form of half-globes which are borne in symmetrical pairs along the branches, giving the effect of a stylized Chinese scroll painting. The variety grandiforum, with larger leaves and flowers than those of the type is the best form to grow.
Continuity of display
In the rather barren weeks that follow the peak flowering period, hydrangeas are a first-class standby. Apart from the large-leaved species, which require partial shade, they will thrive either in full sun or semi-shade. In the former position, however, copious watering or regular mulching will be required during the first few seasons after planting. H. macrophylla is the well-known and deservedly popular pot hydrangea of the florists’ shops. It will also do well out of doors in most parts of the British Isles, although in exposed positions and inland districts the blossom buds, which begin to swell very early in the year, may suffer frost
damage. This can often be prevented by leaving the previous year’s flower-heads on the plants as protection, but in really cold areas it would be safer to plant one of the completely hardy species such as H. paniculata, H. villosa, H. serrata or the oak-leaved hydrangea, H. quercifolia.
Another genus of late-flowering shrubs, useful for bridging the gap
between the summer and the beauties of autumn leaf color is represented by the hypericums, or St John’s worts, of which, the best-known member is the prolific, weed-smothering H. calycinum, the rose of Sharon. For the shrub border, however, the taller species and hybrids are a good deal more useful and decorative. Their flowers, like giant buttercups with a central boss of contrasting stamens, make them among the finest shrubs for a late summer display. `Hidcote’ and ‘Golden Cup’ are both outstanding forms of H. patulum, with large cup-shaped flowers 5-6cm (2-24in) across. H. elatum `Elstead’ is another attractive form, with oval leaves of a fresh vernal green, and masses of small yellow flowers in July and August that are followed by scarlet fruits.
But the outstanding member of the group is undoubtedly the hybrid, `Rowallane’. Unfortunately, it is not completely hardy in all parts of Britain and needs a sheltered position in many areas. Its magnificent golden chalices are 6cm (21in) in diameter and well-developed specimens reach a height of 2.6m (8ft) in milder districts.
To wind up the floral display for the season there is the so-called shrub hollyhock, Hibiscus syriacus, together with the blue-flowered Caryopteris x clandonensis, which is best treated as a herbaceous perennial and cut back almost to ground level each spring.
Shrubs for autumn leaf color
The beauty of the shrub border is not restricted to its floral display. From September until final leaf fall comes a brilliant cavalcade of colored foliage, followed by, and sometimes simultaneous with, beauty of winter berry and bark.
Among the shrubs the leaves of which color so brilliantly, the barberries and cotoneasters play a prominent part.
Berberis thunbergii has small leaves of a clear green that produce a brilliant
flame in autumn. The leaves of the variety atropurpurea, which are deep purple throughout the summer, assume even more dazzling colors before they fall. B. verruculosa is an evergreen species, but many of its dark green leaves turn scarlet, while some of the foliage of the closely related Mahonia aquifolium, another evergreen, turns coppery-red in autumn and winter.
Although, botanically, the cut-leaved Japanese maples are not shrubs, but small trees, they have so many of the characteristics of the former that they are usually included in this category.
The Japanese maples are very slow growers and the purple-leaved Acer palmatum dissectum atropurpureum and its green-leaved counterpart, palmatifidum, both with leaves like the finest lace, never exceed 2-3m (8-10ft) in height. The leaves of the former turn a vivid deep scarlet, while those of the latter color to a lighter but no less distinctive hue.
Anyone who gardens on the moist, peaty soils in which rhododendrons and azaleas thrive ought to find room for Enkianthus campanulatus, which enjoys similar conditions and puts on a spectacular autumn display in orange and red. The Ghent azaleas, too, can be very colorful in autumn, as also can the common yellow Azalea pontica (Rhododendron ponticum) when its sage-green leaves burst into tints of flame and coral.
One of the most unusual and striking shrubs for autumn color, is a member of the euonymus genus, of which the spindle tree is probably the most representative. E. alata has leaves that turn a bright glowing pink. After they fall, continuing winter interest is provided by the curious corky wing-like excrescences on the stems.
All the cotinus and rhus, related genera, are noted for their brilliant autumn color. The stag’s horn sumach, R. typhina laciniata, is particularly spectacular, but this small tree colors rather early for the main autumn display and the display itself is somewhat short-lived. Much more satisfying are the brilliant orange and scarlas of Cotinus americanus (Rhus cotinoides), or the bright yellow of the smoke bush, Cotinus coggygria (Rhus cotinus) .
Among wall shrubs and climbers many of the vines and creepers color magnificently, particularly the giant-leaved Vitis coignetiae, Vitis inconstans (syns. Parthenocissus tricuspidata veitchii, Ampelopsis veitchii), and the true Virginian creeper, Parthenocissus quinquefolia. Where space is restricted, the smaller‑ leaved and less rampant Parthenocissus henryana is useful for providing a wall tapestry of brilliant color.
On the ground, too, creeping and prostrate shrubs such as Cotoneaster horizontalis, Gaultheria procumbens and others will be putting down a red carpet, while the hypericums, that have only just finished their flowering season, will be adding to the autumn colors. Hypericum patulum forrestii has the most brilliant foliage of any of these.
Beauty of berry and bark
Just as decorative, but with a longer lasting effect are the berries of many shrubs. These will continue the display from leaf fall until the New Year—sometimes even later in districts where birds are not numerous.
Once again, the barberries and cotoneasters are well in evidence, with species and varieties bearing fruits of many colors, ranging from the vivid coral red of Berberis ‘Bountiful’ to the grape-purple of B. darwinii. Among the striking forms are B. ‘Buccaneer’ and thunbergii, both with bright red berries and both, incidentally, also providing attractive leaf color. ‘Cherry Ripe’ has fruits that are salmon-red and pear-shaped; the compact, free-flowering Formosan species, B. morrisonsiensis, bears larger red fruits than most.
More than a dozen kinds of cotoneaster share this same valuable quality. The better known varieties include C. horizontalis, whose herring-bone set branches are packed with scarlet button berries and C. simonsii, a popular shrub for hedging and cover planting, with no less brilliant berries the size of peas. Taller forms and species include C. cornubia with large berries borne profusely, C. frigidus with clustered crimson fruits and C. salicifolius, the willow-leaved cotoneaster, that bears heavy crops of bright red fruits. Among the prostrate forms suitable for the rock garden, or for use as ground cover, dammeri decks its trailing shoots with berries like blobs of sealing wax, while C. adpressus has both autumn fruits and bright scarlet foliage.
The pernettyas are a group of attractive small-leaved evergreen shrubs with showy marble-sized berries of an unusual beauty. Not many of them, however, are self-fertile so that a specimen of the type plant, P. mucronata, will have to be included to cross-fertilize the more decoratively-berried forms. These last-named include ‘Donard White’ and `Donard Pink’ (the names are descriptive of the color of their berries), lilacina, with lilac-pink fruits and ‘Bell’s Seedling’ with extra-large, dark-red berries.
The vacciniums, like the pernettyas, are ericaceous plants, and they include the edible North American swamp blueberry, V. corymbosum, and others such as V. macrocarpum, the American cranberry, a prostrate evergreen, the large scarlet berries of which are used for cranberry sauce traditionally associated with the Christmas turkey. V. myrsinites, the evergreen blueberry, is a graceful compact shrub that bears its blue-black berries in May and June when they are of doubtful value for garden decoration.
It is not always realized that certain shrubs are dioecious, for example, the
male and female flowers are borne on separate plants, so that a specimen of each sex will need to be planted if berries are to result. Japanese laurels or aucubas all share this specialized sex characteristic, which makes it difficult for the owner of a small garden, with limited space at his or her disposal, to include many of them in the planting plan. But for those with room to spare all of these are well worth growing, not only for the beauty of their berries but also for the year-long decorative qualities of their handsome, evergreen foliage.
Finally, to act as a foil to the winter-flowering shrubs, there’ are other plants whose main attraction lies in their strikingly-colored bark or interesting branch formation.
The dogwoods, both the scarlet and yellow-stemmed species, love moisture. They will respond to waterside planting and nothing looks more striking in January sunshine than a group of the scarlet-stemmed Westonbirt dogwoods (Cornus alba sibirica) at the edge of a pond or stream, while the curiously twisted stems and branches of Corylus avellana contorta, popularly known as Harry Lauder’s walking stick, make an unusual and interesting tracery against winter skies.
It is impossible, in the space available, to lay down principles of pruning in any but the most general terms. As a general rule, however, spring-flowering shrubs can be pruned after they have finished blooming. Those that flower in summer and autumn, on the current year’s wood, can have their season’s growths cut right back in March of each year.
Shrubs should normally be allowed to develop their natural form and dimensions, but any particularly vigorous growths that appear in the second and third seasons after planting should be tipped when they are between 1525cm (6-9in) long to induce the formation of laterals to build up a solid framework.
Most shrubs, once established, will need little or no attention as far as pruning is concerned, apart from cutting out weak, straggling, diseased or dead shoots. In any case, drastic pruning is an operation that should always be undertaken with caution and should normally be resorted to only when shrubs have been neglected or when, like buddleias, forsythias, flowering currants and the larger philadelphuses, they grow too rampantly and exceed their allotted quarters, or trespass on paths and lawns.
Avoid, at all costs, indiscriminate clipping with the garden shears. Such treatment will not only reduce all your shrubs to a monotonous uniformity of shape but will also result in weak, straggling growth. Clearly this would look unattractive.
This, too, is a vast subject. Many shrubs can be grown easily from seed, although not all of them ripen their seed in this country and it may be necessary to obtain it from specialist seedsmen. Brooms, for example, will germinate as easily and as freely as sweet peas; other shrub seeds, berries in particular, need to be stratified, that is, over-wintered in moist sand, to rot the fleshy seed covering, before they can be sown with any hope of success.
Propagation from hard-wood cuttings is another simple method by which many shrubs may be increased. These cuttings should consist of ripened side shoots that have not flowered, pulled off the parent stem with a heel of bark attached, and inserted in a moist shady bed in July and August. They are left until the end of the following season, when sufficient root and top growth should have developed to enable them to be grown on in a nursery bed.
Shrubs that may be propagated easily by this method include cornus, weigela, deutzia, philadelphus, rhus, cotinus, hydrangea and many other well-known kinds. Hedging shrubs such as privet or Lonicera nitida are easier still. Trimmings stuck into the soil almost anywhere will usually root very quickly.