Hedges perform all kinds of functions. From windbreaks, screening unsightly fences and buildings, creating boundary lines, dividing a garden into specific spaces, highlighting lines or to provide a backdrop for a contrasting foreground.

When thinking of hedges, they can be easily relegated to two groups - formal and informal. This can usually

be defined by the species used and how it is kept (pruned and clipped or natural form) 

A formal hedge will usually use a certain tree or plant, species with small leaves will give a denser and overall neater appearance due to the ease of defined pruning. 

Architecturally, the use of straight lines, symmetry and repetition defines a formal garden. 

An informal hedge will have a free growing form, so any vigorous growing shrub can be used

When designing a garden, often the initial starting point is the structural elements, like retaining walls, decks & pergolas, hard surfaces etc. Hedges, whilst still part of the planting offer a structural element to the design. I like to have hedging at the front of mind during the conceptualisation process, while drafting the functional analysis

Some tall trees that work well as hedges are:

Acmena smithii (lilly pilly)

x Cupressocyparis leylandii ‘Leighton Green’

Ficus microcarpa var. Hillii ‘Hill’s fig’

Prunus laurocerasus ‘cherry laurel’

Waterhousea floribunda ‘weeping lilly pilly’

Medium size: 

Camellia sasanqua

Laurus nobilis ‘bay laurel’

Murraya paniculata ‘orange jessamine’

Photinia x fraser (red robin)

Viburnum odaratissimum (Sweet viburnum)

Smaller hedges:

Buxus microphylla var. Japonica (Japanese box)

Buxus sempervirens (English box) 

Lavandula angustifolia ‘Hidcote’

Lonicera nitida (box leaf honeysuckle)