Shrubs

What are Shrubs?
Shrubs are woody-stemmed plants, usually freely branching from the base. Whereas a tree usually has a single stem, a shrub has several or many stems arising from or near ground level. Most shrubs reach no more than 15-20ft (5-6m) in height, the majority of species and cultivars attaining considerably smaller stature. However, a degree of overlap occurs between shrubs and other plant groups. Larger shrubs that grow on a single stem, such as some viburnums, can be considered trees, although this depends on their size at maturity. Subshrubs (shrubs that are woody only at the base), such as Perovskia, and shrubs that die back annually as a result of winter cold, such as Fuchsia, are often cultivated as herbaceous perennials.

Essential framework
In every size and style of garden, shrubs are invaluable for their structural forms and their woody stems, which provide the garden with a long-term framework. They offer a variety of shapes and sizes, from prostrate, mat-, or clump- forming subshrubs, such as dwarf cultivars of Erica carnea, only 6in (15cm) high, to erect, tree-like shrubs like Buddleja colvilei, 20ft (6m) tall.

Ornamental features
Shrubs display an immense range of decorative features. They are often cultivated for their foliage, occurring in many shades of green, yellow, red, purple, silver, or gray. Some are especially favored for their brilliant autumn coloration: Japanese maples (Acerpalmatum) include numerous cultivars that turn from yellow through orange to shades of red, while the leaves of some Cotinus cultivars turn red between autumn and early winter. The notable autumn leaf color of witch hazels (.Hamamelis) ranges from yellow to orange-red or purple. The flowers of shrubs vary enormously in shape, size, and scent, and occur in almost every color. At one end of the spectrum are the abundant, tiny flowers of Ceanothus; at the other are the giant blooms of tree peonies (Paeonia). While numerous shrubs bloom for only a few weeks each year, others, including Hypericum and Potentilla, flower reliably over several months; shrubs of the latter type are valuable during periods when little else is in bloom. Some shrubs, such as Mexican orange blossom (Choisya ternata), are remontant, regularly flowering twice a year. Late-winter- flowering shrubs, such as Viburnum x bodnantense, often bear scented blooms over a long period. Many popular shrubs, including Cotoneaster, holly (Ilex), Pyracantha, and Viburnum, bear vividly colored berries in autumn, which persist into winter. Other types of fruit range from those of Dipelta, which are covered by papery bracts, to the pendent, bean-like, deep blue pods of Decaisnea fargesii. Some shrubs display brightly colored winter stems. In dogwoods (Cornus), the stems can be blazing red through to bright greenish yellow. They are usually coppiced to stimulate new growth for the best display of color.

Garden uses
Most shrubs are grown in a shrub border, or in a mixed border among annuals or perennials.  When designing a border, it is advisable first to establish a theme.  Consider whether the border is to display a selection of favorite species or to provide interest in a particular season or throughout the year, and whether plants should feature ornamental or scented flowers, decorative foliage, fruit, or various combinations of all these. For an all-season shrub border, select larger shrubs that will flower in different seasons: for example, choose Viburnum sargentii to flower in spring, lilacs (Syringa) or Philadelphus for flowers in summer, and witch hazel (Hamamelis) or Garrya elliptica for autumn or late-winter blooms.  For year-round foliage interest, include both deciduous and evergreen shrubs.

Shrub borders are usually designed with larger shrubs planted at the back of the border, and dwarf or groundcover shrubs, such as Chaenomeles japonica, at the front, although other arrangements can also be successful.  It is particularly important to provide sufficient space for each shrub; as plants become established, they should not crowd one another.  If necessary, any bare patches can be filled in with small, fast-growing shrubs, such as fuchsias, potentillas, or spireas, which can be removed when shrubs with a slower growth rate have reached maturity.  Some shrubs are best trained against a warm, sunny wall, particularly tender shrubs, which may not thrive elsewhere in the garden; a few, such as Ceanothus, may grow to twice their usual height in this situation. In a mixed border, cultivate shrubs alongside annuals, biennials, bulbs, or herbaceous perennials, seeking associations of color and texture of flowers and foliage, and contrasts in form and habit.  When dividing or transplanting perennials within a mixed border, take care not to damage the roots of nearby plants.  Shrubs that exhibit a variety of ornamental features make excellent specimen plants and are ideally sited where they may be viewed from different angles.  A specimen shrub should be appealing in habit and branch structure, particularly if it is deciduous, as well as in its foliage, flowers, or fruit.  In a small garden, where a single specimen serves as a focal point throughout the year, versatility is essential; it is less important in a large garden that can accommodate a selection of shrubs of different sizes and features.

Growing in containers
Many shrubs thrive in containers and are excellent for a small garden, patio, or roof terrace.  Use an isolated specimen in a decorative container as an arresting focal point, or  group containers in different arrangements for variety. Container growing also enables cultivation of shrubs that may not survive in the open garden due to the pH or drainage of the local soil, or an unsuitable climate.  Tender plants can be grown outdoors in summer, and then moved indoors before the first frosts.  Ensure that hardy plants kept outside are grown in frost-proof containers.

Cultivation
Shrubs will thrive for many years, given the right growing conditions.  The majority will grow in many types of garden soil, but generally prefer a fertile, well-drained but moisture-retentive loam.  Plant bare-root and balled-and-burlapped shrubs in autumn or spring, although planting should be avoided if the ground is frozen.  Container-grown plants can be planted at any time, but usually established best if planted in autumn or spring. For balled-and-burlapped or container-grown plants, make the planting hole 2 or 3 times the width of the root ball and deep enough for the roots to be buried to their original depth of soil.  For bare-root plants, allow room for the roots to fan out fully around the shrub.

Plant the shrub, backfilling with a mixture of soil and organic matter, and firm in.  In sandy soils, leave a depression around the shrub to retain moisture; in clay soils, plant the shrub slightly higher than the surrounding soil level so that water will readily drain off.  Water and mulch well with compost or bark chips.  Protect newly planted shrubs from cold, drying winds.  Plant wall-trained shrubs about 18in (45cm) from the wall; lean the plant against the wall, and support it with stakes tied into wires.  Young plants require regular watering until established.  Apply fertilizer in early spring, and mulch thickly with bark chips or compost in spring or autumn.

From early spring to midsummer, water shrubs in containers freely and apply a quick-release fertilizer 2 or 3 times.  In spring, replace the top 2-4 in (5-10cm) of soil mix with fresh soil mix, mixed with a slow-release, balanced fertilizer.  Pot on in late summer or autumn when the root growth appears congested. For all shrubs, remove suckers and cut out reverted (plain) shoots from variegated plants as son as they appear. Deadhead regularly to encourage stronger growth.

-Information obtained from The American Horticultural Society A-Z Encyclopedia of Garden Plants