Plants can be used as windbreaks, hedges and screens to form a living, physical barrier. They can provide a quick growing, colorful alternative to a fence, wall, or other hard barrier.
There are many reasons for creating a plant barrier:
A row of plants provides privacy from neighbours and the street, or can block out your view of unsightly areas.
Noise control this is done best in conjunction with an earthen mound. A single row of plants might not stop much noise.
Wind and temperature control eg: hot, dry winds.
As a physical barrier eg: to contain animals and children
For a a visual barrier to differentiate areas of a garden eg: a low hedge enclosing a rose planting
A visual barrier, hiding unsightly parts of a garden eg. solid hedge around rubbish bins or a compost heap.
A living screen is a row of plants grown closely together to block a view. Screen plants must have foliage dense enough to block the view. Screens can be like hedges, but they are not necessarily pruned.
A hedge is a row of plants grown close enough together that their foliage intertwines to form a solid barrier. They are normally pruned (distinguishing them from screens). The foliage is very dense, forming not only a visual barrier but also a physical barrier.
A windbreak is a row of plants used to slow or deflect the wind. It may be dense foliage which deflects or stops most of the wind, or not so dense allowing some wind through, but slowing most of it.
When selecting your plants consider the amount of space that you have available, the desired height of the hedge, how quickly the hedge must establish, how often you are prepared to trim the plants and any special function that you want the hedge to perform (for example, a prickly hedge might be used to discourage access by people or animals but would not be appropriate in a children's play area).
To create a hedge, trees or shrubs are planted closely together than if they were planted in a garden bed as a specimen plant (hedge plantings are generally about one third of the normal spacing).
Most slow or medium growing hedges only require clipping twice a year, though they are slow to establish (perhaps up to 8 or 10 years to reach 2 metres tall).
Fast growing hedges are much quicker to establish, but require far more frequent pruning; perhaps every few weeks in the growing season.
If a hedge is not cut regularly, it can sprawl, requiring hard cutting into older wood which doesn't bear leaves. Hard cutting like this on some plants (eg: conifers) can result in die back of hedge sections.
Prune small leaved hedges with hedge shears or an electric trimmer. Until you become proficient, it can be useful to tie a string along the length of the hedge to use as a guide when pruning.
Hedges should always be pruned to be slightly narrower at the top than the bottom, to minimize shading of the lower foliage.
Hedges for Windy Sites
Crataegus monogyna Plant them 0.3m apart, slow to medium growth rate to between 1 and 3 metres tall
Fagus sylvatica Space 0.4m apart, medium growth rate, 2 to 5m tall
Pyracantha coccinea Spacing 0.7m apart, 1 to 2m tall and medium growth rate
Rhododendron ponticum Plant the plants 0.7m apart. They have an average growth rate and reach 1 to 3m tall
Tamarix species Spacing is 0.4m, medium to fast growing, 2 to 3m tall
Taxus buccata 0.7m spacing, slow growing, 1 to 3m tall
Viburnum tinus 0.5m spacing, medium growth rate, reaching 1 to 2m tall
Hedges for clay soils (with some protection)
Berberis darwinii 0.5m spacing, Slow to medium growth, up to 2m tall
Berberis thunbergii 0.4m spacing, Medium growth, to 1.5m tall
Buxus sempervirens 0.3m spacing, Slow growth, but long lived, up to 1m tall.
Chamaecyparis lawsoniana 0.7m spacing, Slow to medium growth, 2 to 10m tall (varies between varieties)
Cupressus macrocarpa 1 to 3m spacing, medium to fast growth rate, height variable but can be very tall (over 10m) and unmanageable if not regularly trimmed.
Escallonia macrantha 0.7m spacing, medium growth rate, up to 3m tall
Euonymus alatus 'Compactus' 0.5m spacing, medium growth rate, up to 1.5m tall
Ilex aquifolium 0.8m spacing, slow growth rate, 2m to 8m tall depending on cultivar
Ligustrum ovalifolium 0.5m spacing, fast growing, 2m to 4m tall
Lonicera nitida 0.3m spacing, fast growing, looks similar to Berberis, 0.5 to 1.5m tall
Photinia robusta 0.5 to 1m spacing, irregular growth rate, 5 to 7m tall
Thuja plicata 0.8m spacing, medium growth, to 5m height.